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Mammalogy Lecture 14 Arvicoline Population Cycles Population Cycles For the most part populations tend to be fairly stable They may uctuate but there s usually an identifiable correlate that we can associate with population size A This is not true for many murid rodents in the subfamily Arvicolinae voles and lemmings 1 Examples Clethrionomys rufocanus in the Kola peninsula Dicrostonyx in Alaska Several wellstudied species osz39crotus Cycle also occur in Lepus americanus Lymc canadensis 2 Characteristics of arvicoline cycles 1 Peak population densities may actually be 12 orders of magnitude higher than trough densities The highest reported were M montanus of 20000 per hectare 2 Growth phase is very rapid 3 Crash is very abrupt 4 Typically in arvicolines there are 35 years between peaks there is a lag 5 This periodicity seems to be fairly regular that is nonrandom at least in the temporal aspect although the amplitude of the peak can vary There are some questions regarding the statistical regularity of these cycles but not about the existence of the cycles themselves In addition there is a latitudinal component There is a correlation between the tendency to cycle and latitude northern more cyclicity Especially true in Scandinavia B Biologists have been struck by this phenomenon for some time and a great deal of work has been undertaken to uncover the cause of these cycles 1 Need to explain 1 Rapid growth 7 easythese are quintessential rselected mammals V 2 Why does growth stop 3 Why is decline so steep 4 Why is there a time lag 2 Extrinsic Hypotheses a Food HerbivorePlant interactions Batzli and others At low vole densities plants are unaffected by herbivory At high densities there is a selective reduction of plant biomass A high rate of herbivory is induces the production of chemical defenses by plants This in addition to an overall reduction in biomass compromises the quality of forage available to voles which in turn causes the crash The time lag is explained as the time that plant populations take to recover Slide Graph on slide right represents a mathematical model based only on food and a time lag corresponding to plant recovery Actual populations seem to fit predictions of the mathematical models extremely well so this hypothesis has been tested experimentally When voles are raised in enclosures and given supplemental food we still eventually see a population crash Exhaustion of food resources alone can t explain crash These studies have been repeated again and again Supplemental food just can t prevent a crash Therefore the food hypothesis can t be the only explanation Predators In northern Scandinavia there are specialist predators gt M ustela m39valz39s M erminea The idea is that specialist predators oscillate with prey as is the case with snowshoes and lynx and predators drive the cycle In southern Scandinavia the predators are more generalist and keep populations relatively low because the predator populations never crash This would explain the latitudinal variation However the correspondence between specialist predators and latitude doesn t hold in North America and populations in predator free enclosures still crash Thus predation alone can t explain arvicoline population cycles 3 Intrinsic Hypotheses Chitty Hyopthesis BehavioralGenetic hypothesis Based on the observation that there is a higher proportion of large aggressive voles in peak populations Idea is that there is a genetic basis to both size and aggressive behavior and that selection is operating within a cycle It s complex but the crux is as follows At low densities selection will favor Clark Kent voles amicable put much energy into reproduction rather than aggression At high densities selection will favor fighters they ll get resources but won t be very reproductively active 9 population will crash At first the Chitty hypothesis was criticized on the grounds that a single cycle is too short a time period for selection to operate However allozyme studies have demonstrated that allele frequencies in a sample from a trough can be significantly different than those in a sample from a peak So significant genetic change can actually occur in this short a time period w in a cycle This led to a general acceptance of the Chitty hypothesis and the old text listed this as the explanation Problem the traits involved large size and aggressive behavior have very low heritabilities gt even though genetic change within a cycle can be driven by selection not true for the crucial traits 4 Multifactorial Hypothesis Hestebeck et al At low densities Scattered social groups Group size is regulated by dispersal there is free dispersal Little aggression because there are plenty of resources Intrinsic factors will dominate the dynamics of the pop At high densities Resources become scarce Food may become limiting Dispersers experience increased aggression because of lower relatedness Further dispersal will be curtailed and population may increase to the point of exhausting resources Extrinsic factors will dominate Population will crash Clearly a multifactorial explanation will be required see page 396 in your text This actually includes many of he aspects of each of the single factor hypotheses Food becomes limiting this contributes to other effects such as increased aggression Predators are incorporated by Pantry Effect predation increases greatly at high vole densities because of a positive feedback even among generalist predators This contributes to crash Accounts for large aggressive animals present at high population densities Population cycles in arvicolines is a complex phenomenon and the explanation isn t going to be simple and multifactorial hypotheses will be required However one difficulty that such a complex hypothesis presents is that it is incredibly difficult to test Mammalogy Lecture 3 Early MammalsMonotremes 1 Early mammals These groups are known as Mesozoic mammals and there are several groups Again there have been lots of new groups discovered and we ll only address a few that are important for one reason or another A Morganucodontids Remember that this node represents our cladebased de nition Mammalia These are some of the earliest known mammals from the latest Triassic and early Jurassic They re best known from the genus M organucodon We actually have pretty good complete fossils for this group so we can make quite a few inferences Small 7 The skull length was around 3 cm and total length around 10 cm Skull had large nasal cavity We can infer that there were great olfactory capabilities and that there were respiratory turbinates so they were probably endotherms Welldeveloped inner ear region 7 large petrosal They probably had very good hearing In addition they had very large eye sockets Based on this as well as the olfactory and auditory capabilities we can infer that they were probably nocturnal Dentary was greatly expanded and articulated with the squamosal but the articular was small and still present Thus they had a single ear ossicle They had no auditory bullae The tympanic bone is not fused to cranium rather the angular is on mandible Cheek teeth had three cusps large middle cusp with the anterior and posterior cusps offset alternate side chewing upper amp lower slid past each other and we see wear facets that resulted in shearing probably insectivorous They were diphyodont and some have used this to infer the presence of lactation The pectoral girdle was like early cynodonts even early synapsids scapula anterior amp posterior coracoids clavicle and intercalvicle present They almost certainly had vibrissae whiskers based on pits and openings in the snout So they had hair B Triconodonts 7 Prior to a few years ago triconodonts were known only from teeth and a few other skeletal fragments These are similar to Morganucodontids except the cusps are linear A complete Triconodont skeleton was discovered in China a few years ago the genus Jeholodens A really spectacular aspect of Jeholedens is that they have a very mammalian pectoral girdle Only a scapula and clavicle 7 The coracoids and interclavicle are lost But the pelvic girdle is still ancestral 7 ilium ischium and pubis are separate epipubic bones are present Still had a very sprawling posture 7 limbs were not rotated under the body It s therefore a good demonstration of mosaic evolution The pectoral girdle is derived but the pelvic girdle is primitive 1 1 Just last year an 39 quot 39J cool ti39 was ii v d This is the largest mammal known from the Mesozoic about a meter long and probably was carnivorous In fact in one specimen of the genus a collection of bones from a small dinosaur were found where the stomach would have been suggesting predation on dinosaurs Hu et al 2005 Science 433139 7 pdf on website These also had the derived mammalian pectoral girdle but retained the ancestral pelvic girdle C Multituberculates aka Rodents of the Mesozoic This is a very diverse and persistent group It is rst known from the upper Jurassic and ranged from mousesized to marmotsized They extend through the Cretaceous into the Tertiary and existed with modern mammals They are named for their unique dentition and the thinking is that this is what allowed them to persist as long as they did and become diverse There are chisellike incisors or front teeth with a large diastema gap between front and cheek teeth This is associated with herbivory They had very complex grinding molars this is the character for which they re named Many of these are characteristic of modern herbivorous mammals Their success is thought to be related to their dentition in that their diversi cation persistence and diversity coincides with the early Cretaceous diversi cation of owering plants angiosperms The hypothesis is that because of their specialized dentition they were able to diversify into the many new herbivore niches that were available with the diversi cation of owering plants There s good evidence that at lest some of the multituberculates were arboreal A really intriguing aspect of this group is that as judged by their pelvis they may have been viviparous although that s a dif cult inference to test D Pantotheres This group has recently been shown to be paraphyletic so we ll use it informally It probably represents a series of groups progressively more closely related to living therians Mid Jurassic These were long thought to be the earliest mammals to have bifunctional teeth a single cheek tooth has both grinding and shearing function Tribosphenic molars and is thought to be the primitive tooth type for living mammals We ll talk more about tribosphenic molars when we discuss dentition because there are groups that have retained this type of tooth E Other new fossils 7 A large amount of new fossil material has recently become available I ll just mention a few 1 Some wild Australian fossils have been discovered that exhibit tribosphenic molars Rich et al 1997 Science 278 1438 7 pdf on course website It was originally thought that these were eutherians based on their tribosphenic molars However the phylogeny I referenced Luo et al 2002 7 see the copy on course website indicates that these fossils eg Bishops Auskm39bosphenos are related to Monotremes This is extremely interesting because it implies that bifunctional teeth evolved twice 2 The genus H adrocodium is the oldest known mammalian fossil It was discovered just a few years ago Luo et al 2001 Science 292 1535 and appears to be ca 195 MY old As you can see it s a very tiny specimen and there s controversy over whether it s an adult or not 3 The genus Eomia was discovered a few years ago Ji et al 2002 Nature 416816 7 pdf on website This is the oldest eutherian ca 125 MY old and has a number of adaptations that suggest it was scansorial adapted for climbing Over the next several years it ll be very interesting to see how the increasing knowledge of nonmammalian cynodonts and early mammals impacts hypotheses such as the size refugium hypothesis This is particularly true of some newly discovered fossil sites in Wyoming All the earlier known sites were examined in the late 1800 s and paleontologists only paid attention to the large fossils Bishops left lnwer jaw in buccal occlusal Er lingual views me Rich et a1 2001 Nate that le cmtum nf m jaw has been memedby crushing Hadmcadmm 11 Living Mammals Monotremes vs Therian Mammals Relationships are most likely as I have them on the overhead Metatherians and Eutherians form a clade called Theria Monotremes including their ancient relatives Old View is that quot 39 39 lllUl J quot J and tr39 J formed a group called Prototheria You ll still see the term used for example in your text Currently the bestsupported hypothesis of relationships is as shown making Prototheria a paraphyletic group A O Monotremata one hole refers to cloaca which is the latin word for sewer The cloaca is a single opening receives the large intestine ureters and reproductive tract very primitive trait among vertebrates Earliest fossils are from the early Cretaceous gt 120MYA Fossil record is still poor but it is increasing A few years ago a fossil 63 MY old platypus fossil was discovered in southern South America The fossil had teeth similar to the teeth living platypus has when young B We often hear monotremes called primitive mammals gt really is inaccurate because monotremes are mosaics of both primitive and derived traits Primitive Characters Cloaca still present in other tetrapod groups Skull characters still posess pre and post frontal bones no auditory bulla lacrimal bones absent Pectoral girdle interclavicle anterior coracoids posterior coracoids intercalvicle Cervical ribs are present and free that is not fused to vertebrae Epipubic bones 7 present in early synapsids Reproductive characters oviparous eggs have huge amount of yolk relative to therians eggs are shelled have a shell gland mammary glands have separate openings no nipple and young lap milk from tufts of fur rather than suckling male lacks a scrotum and testes remain in the abdominal cavity males lack seminal vessicles Derived Characters Leathery bill or beak As adults instead of teeth they have horny raspy pads Venom male platypuses have a venomous spur This is very unusual in mammals Electroreceptors in bill in platypuses One group has spines It s a mischaracterization to call a group primitive C Two living groups both restricted to Australia and New Guinea 1 F Tachyglossidae Echidnas occur in both Aust amp NG Both forms have large spines not barbed like those of porcupines when threatened echidnas will roll up into a ball Pinnae external ears are moderately large Limbs are powerful and adapted for digging Typically lay single egg that is incubated in a temporary pouch for 710 days Echidnas hibernate that is when ambient temperature drops to 5 degrees C gt Tbody drops to 55 degrees Males have spurs but these are nonvenomous Tachyglossus short beaked echidna specializes on ants and termites has copious sticky saliva Zaglossus long beaked echidna specializes on ea1thworms 2 F Omithorhynchidae Platypus found only in Australia Ornithorhynchus Aquatic swims with forefeet which are webbed digits retain claws BirdSnout feed primarily on aquatic crustaceans submerge for around a minute dense pelage and under fur is wooly males have venomous spurs that enlarge during reproductive season gt maletomale combat young platypus have teeth that actually never erupt electroreceptors in bill prey detection burrow into stream bank make a den usually lay two eggs which are incubated for 10 days in the plugged burrow We actually didn t learn much about this ecology until the 70 s Mammalogy Lecture 11 Reproduction I General Patterns 1 Obviously reproduction is a very important aspect of biology and whole courses are dedicated to it It s easy to understand why reproductive traits would be subject to strong selection because of their direct effects on tness 11 As we might expect there are three basic types of mammalian reproduction These correspond to the three major groups of mammals Differences among these types re ect the degree of intimacy of fetalmatemal contact A Monotreme Type Retain the primitive amniote pattern but add a period of lactation Egg is very large at ovulation about 3 mm It moves down the oviduct where it is fertilized then it s coated with albumin then a shell is laid down by a shell gland and the shell is mineralized with CaC03 Embryo spends 23 weeks in the uterus then it s laid It s large 15 mm when it s laid Embryo growth is supported entirely by the yolk that s enclosed in the egg B Metatherian type In some superficial ways it s similar to monotremes in that metatherians retain a shell membrane around the fertilized egg a shell gland is present in Miillerian ducts However the shell is never mineralized and young are born live after only ca 12 days as we ve seen they are very altricial poorly developed Initial intrauterine growth is supported by maternally by a placenta Metatherian placenta is the choriovitelline type yolksac placenta Eutherian placenta is called chorioallantoic placenta C Placenta Formation Let s look at formation of the placenta in Meta amp Eutherians Placentas are formed from three layers in both groups A single maternal layer is the endometrium The inner lining of the uterus is highly vascularized and this is what is shed during human menstruation The chorion is the outer embryonic layer which is derived in part from the trophoblast An inner embryonic layer varies There are two options Vitelline yolk sac in metatherians allantois in eutherians Early embryonic stage is similar for both Eutherians and Metatherians In metatherians attachment of the embryo to the uterine wall is very super cial it sinks into a shallow depression and there is almost no erosion of the uterine wall The vitelline expands greatly and surrounds the embryo and the allantois shrinks This results in the Choriovitelline placenta 0f metatherians Maternal nutrients are taken up very indirectly A uid called uterine milk bathes the embryo and nutrients diffuse into the yolk sac It s not really milk at all but a nutritive uid secreted by the uterus There may be some degree of wrinkling of the chorionic surface at the point of contact with the endometrium This increases the surface area across which diffusion can take place but only by a small amount In this system then there is no direct contact between fetal and maternal circulation Nutrient transfer is relatively inefficient nutrients diffuse from the uterine milk As we ve mentioned young are born altricial after a very short gestation and continue development in marsupium or at least anchored to the mammae In eutherians the vitelline layer always functions very early in development to nourish the embryo but it quickly recedes Chorioallantoic type There is much variation in how intimate the fetalmatemal contact is but all eutherians have more intimate contact than the choriovitelline type This then leads to greater efficiency of transport of maternal nutrients to the fetus This variation doesn t seem to exhibit a strong correlation with phylogeny As we mentioned the early stages of placentation are similar for eutherians amp metatherians When the zygote contacts the endometrial lining it sinks into the wall rather deeply This is called implantation It results from the erosion of the endometrium In many species including humans implantation is so deep that the endometrium entirely surrounds the embryo The vitelline recedes and the allantois expands greatly to surround the developing embryo The chorion then develops villi which further penetrate the endometrium These villi serve to greatly increase the surface area for absorption and are highly vascularized There is also a great deal of variation in the extent of the villi It s across this endometrium that nutrient transport takes from maternal to fetal circulation place through the chorionic villi Now as I said there is a great deal of variation in eutherian placentae One thing that varies is the degree of endometrial erosion and efficieny of nutrient transfer is directly related to this The more erosion the less tissues separating fetal circulation from maternal circulation There are a number of types that are recognized we ll use 4 examples Figure 914 Is good description of a number of types of eutherian placentas There are at most 6 layers of tissue that separate maternal and fetal circulation Epitheliochor39ial In some eutherians there is relatively little endometrial erosion it s limited to a pocket around the chorionic villi There are six thin layers of tissue separating maternal from fetal circulation Cetaceans Suids and Equids Endotheliochor39ial There is more erosion of endometrium The epithelium and connective tissue erode and the chorionic villi are in direct contact with metemal capillaries Common in Camivora Hemochorial All the maternal tissue erodes including the maternal capillary walls Pools of maternal blood then surround the villi Chiroptera Insectivor ans some primates inclung H0m0 Hemoendothelial Much of the chorionic tissue also erodes and fetal capillaries are actually bathed in maternal blood Fetal capillaries are actually bathed in blood because much of chorionic tissue also erodes Some Insectivora and Rodentia These provide much more efficient nutrient transfer a hemoendothelial insectivoran placenta is 250 times more efficient than the epitheliochorial placenta of a suid D Deciduous vs Non deciduous Placentas In those forms where there is extensive endometrial erosion the maternal portion of the placenta is shed after birth along with the fetal portion This is what is called the afterbirth and it results in lots of bleeding In those forms where there is little endometrial erosion there is no maternal afterbirth little blood nondeciduous It s been suggested that the less efficient placentas are maintained by this difference If there is much bleeding predators may be attracted ie sharks in the case of cetaceans nest locality may be revealed nest may be fouled leading to bacterial infection Peramelids have a chorioallantoic placenta these differ from those of eutherians in that these lack chorionic Villi The surface area is increased only slightly by corrugations or slight folds The embryo is bathed in uterine milk as I indicated for metatherians earlier Mammalogy Lecture 4B Therian Mammal Diversity Eutherians VI Eutherian Groups We won t go through the diversity here in as great detail as we did for Marsupials We ll leave a lot of details for the lab We ll recognize 18 orders of placental mammals For 150 years the relationships among these are a classic problem in mammalogy The reason for this is that in the Cretaceous there was a rapid radiation That is the modern Eutherian orders evolved in a burst which results in a phylogeny that looks more like a bush than a tree with very short internal branches Resolving these relationships has been a very active area of research and a series of papers have been published in the last few years copies in the lab that have made enormous strides We ll use the phylogeny I ve shown in the handout to structure our treatment of eutherian diversity Afrotheria is the name given to the first group This is a group that has its early history in Africa It contains 6 orders 0 Proboscidea Elephants now known only from Africa and Asia Formerly much more diverse and widespread F Elephantidae Asiatic Elephant iElephas Small ears African Elephant iLoxodonta Large ears Back tofront tooth replacement rather than from underneath O Sirenia sea cows Caribbean and Indian Ocean also Amazonian 7 2 families 5 species These are thought to be the source of the mermaid myths Sister to elephants 7 share backtofront tooth replacement F Trichechidae Trichechus manatee O Hyracoidea Hyraxes single family with siX species Herbivorous African F Procaviidae Procavz39a Feet have unique friction pads O Macroscelidea elephant shrews Central and eastern Africa F Macroscelididae 4 Genera and 15 species They re cursorial amp get their name from extended snout M acroscelides O Tubulindentata Aardvark monotypic F Orycteropidae Unique tooth pattern Myrmecophagous have the adaptations long tongue slender dentary etc Orycteropus O Afrosoricida 7 tenrecs and golden moles These two families are traditionally lumped into the order Insectivora However lots of molecular data support their sister group relationship with each other and their inclusion in Afrotheria F Tenrecidae itenrecs 10 genera 24 species Madagascar and westcentral Africa The genus Echinops which we ll see in lab The genus Tenrec which doesn t have hair modi ed into spines The next group is a South American group containing a single order 0 Xenalthra Edentata Sloths anteaters and armadillos 4 families 29 species South American formerly very diverse One group has invaded N Am Are characterized by an additional articulation between successive vertebrae formed by the xenarthrous process a structure unique to this order F Myrmecophagidae Anteaters 3 Genera and 4 Species all S American All are myrmecophagous extremely long snout thin delcate dentary long protrusible tongue sticky copious saliva teeth are absent forelimbs are modi ed for digging M yrmecophaga F Bradypodidae 3toed Sloths 2 genera Bradypus 7 threetoed sloth These are arboreal foliavores so they have adaptations for eating low quality food These only descend from trees to defecate 7 may occur once every couple weeks or so The next major clade is called Boreoeutheria and it contains groups with apparent origins in the northern hemisphere Boreoeutheria has two groups of orders Euarchontoglires O Rodentia Rodents are worldwide 29 families split into two suborders 2021 species 44 of all mammals All have evergrowing chisellike incisors a large diastema and grinding cheek teeth SO Hystricognathi Primarily South American and African F Erethizontidae New World Porcupines Only histricognath family that s native to North America Coendu Prehensiletailed porcupine primarily eat bark very arboreal Erethz39zon is the only histricognath that s native to North America F Hydrochaeridae Capybaras Single species H ydrochaeris Largest rodent Stands almost 2 feet high F Bathyergidae Mole Rats 5 G 8 S All subSaharan Africa Trend in the family towards increasingly compleX social behavior H eterocephalus Naked mole rat the only eusocial mammal Only member of the family that s naked SO Sciurognathi world wide probably not be monophyletic F Sciuridae Squirrels 50 Genera 276 Species Worldwide except Australia Spermophilus beldz39ngz39 7 We ll talk about the social system in this species F Heteromyidae Pocket mice and Kangaroo rats and mice 5 Genera 59 Species North American just get into South America The family exhibits two trends Progressively desertadapted forms Progressively saltatorial Microdipodops Kangaroo mouse Enlarged auditory bullae May never actually have to consume water F Geomyidae Pocket Gophers 5 Genera 35 Species Primarily North American Thomomys talpoides Northern pocket gopher Extremely fossorial Fusiform body Small eyes and pinnae Velvety fur Short tactorial tail Claws modi ed for digging 7 front limb later Procumbent incisors protrude from mouth when it s closed F Muridae Rats and Mice 1300 species 30 of all mammals ll subfamilies Sigmodontinae New World Rats and Mice Reithrodontomys megalotz39s Western harvest mouse ArVicolinea Voles and Lemmings Microtus longicaudus Longtailed vole O Lagomorpha Rabbits and Hares 2 families 80 species All have chisellike upper and lower first incisors and small peglike second upper incisors have a diastema are herbivorous Probably the sistergroup to rodents Glires F Leporidae Rabbits and Hares ll Genera 54 Species North America and Eurasia Highly Cursorial including fenestrated rostrum weight reduction Lepus townsendii Whitetailed jackrabbit O Primates 13 families 233 species The order is truly worldwide amp probably evolved from arboreal ancestors Two Suborders based on the condition of the facial region we ll discuss in lab SO Strepsirhini Often referred to as Prosimians Diagnosed by dental comb F Lemu dae Lemurs 4 Genera 5 Species Restricted to Madagascar Representative form is the genus Lemur SO Haplorhini Often referred to as Anthropoids Lack dental comb F Callithricidae Tamarins and Marmosets 4 Genera 26 Species Entirely Neotropical and omnivorous Leontopithecus F Hominidae Great Apes 4 Genera 5 Species Worldwide and omnivorous Once only included humans paraphyletic other great apes were grouped into Pongidae Pan and Homo O Dermoptera Gliding Lemur or Colugo 2 species F Cynocephalidae Phillipines and SE Asia Have a gliding membrane that extends between wrist and ankles Have comblike lower incisors use for grooming Single pectinate tooth Cynocephalus O Scandentia Tree shrews Are shrews but there s been a lot of uncertainty regarding relationships F Tupaidae 7 Asian squirrel like organisms 5 genera and 19 species Tupaz39a Laurasiatheria O Insectivora Worldwide except Australia Lots of groups used to be lumped in here Some authors use the name Eulipotyphla to differentiate the new concept of this order Almost 400 species 7 9 of all mammals F Soricidae Shrews 23 G 318 Sp Worldwide except S America Sorex palusm39s Water shrew Includes a common form Blarina brevicauda that has venomous saliva that it uses to kill larger animals Microtus may comprise 90 of its winter diet 0 Chiroptera Bats are worldwide 17 families also split in to two suborders 925 species 20 of mammals All have powered ight And the ight membrane is supported by the hand hence name This character evolved only a single time SO Megachiroptera Flying foxes or OW fruit bats There is a single family which occurs in the Old World tropics F Pteropodidae Flying foxes primarily frugivorous They rely on vision only one genus echolocates Rousettus the echolocating form SO Microchiroptera Echolocating or microbats These echolocate are worldwide and there are 16 families We ll mention two F Phyllostomidae Leafnosed bats 49 Genera 143 Species Neotropics Lots of diversity in feeding habits frugivorous forms Artebz39us jamaz39censis sanguinivorous forms Nactarivorous Piscivorous and frogeating Desmodus rotundus 7 Vampire bat Complex renal physiology anticoagulant saliva bladelike incisors F Vespertilionidae Vespertilionids 42 Genera 318 Species worldwide All are primarily insectivorous Euderma maculatum Spotted bat Solitary cliffroosting bat Idaho species not represented in our collection 0 Carnivora Majority are meat eaters although there are herbivorous forms There are 11 families including the familiar canids and felids but it also includes the old order Pinnepedia Seals Walrus and Sea Lions Characterized by Camassial teeth adapted for shearing meat 4th Premolar lst Molar below F Phocidae Seals 10 Genera 19 species Aquatic 7 Here represented by elephant seal M irounga We ll talk about at the end of the semester F Procyonidae Racoons and their kin 6 G amp 10 S All in the New World Ringtail Bassariscus O Pholidota 7 Pangolins 7 species Asian F Manidae Manis These may well be the sister group to Camivora Myrmecophagous have the adaptations that typically associate with that Pyloric portion is thickened and muscular with keratinous projections Similar to an aVian gizzard Scales These are formed by agglutinized hairs If you look at them you can see the individual bers that comprise the scales 0 Cetartiodactyla Eventoed ungulates amp whales 20 families 298 species Characteristics of terrestrial forms 3rd amp 4th digits are modi ed Metapodials are elongate and fused into a canon bone The ungula nail homologue is modi ed into hoof Primarily herbivorous but there are omnivorous forms In many families the stomach is multichambered F Suidae Hogs 5 Genera 16 species Native distribution is Eurasia and Africa Omnivorous and include the domestic hog Sus Warthog Phacochaeris Tusks are modi ed incisors 7 used in malemale combat F Giraf dae 2 Genera and 2 species Giraffe unique horns ossicones parietal bones Characteristics of fully marine forms Fusiform bodies Forelimb modi ed into ns Hind limbs lost pelvic girdle vestige remains Whales actually appear to be sister group to Hippopotamidae There are phenomenal fossil intermediates from the terrestrial ancestors of whales we ll address these during locomotion lectures Mysticete whales Named for baleen keratinized plates used in lter feeding F Balaenopteridae Rorquals 2 Genera and 6 Species M egaptera Odontocete whales Toothed whales may be paraphyletic F Delphinidae Dolphins l7 Genera and 32 species Orcinus O Perissodactyla Oddtoed ungulates 3 families 18 species Formerly more diverse and wide spread 3rd digit is expanded and typically have a single hoof Lateral digits reduced Herbivorous have diastema F Rhinocerotidae 4 Genera 5 Species Keratinized horn Ceratotherium White Rhino F Equidae l Genus 9 Species Natural distribution includes only East Africa and Asia although much equid evolution occurred in North America Equus grevyi Grevy s Zebra Narrow stripes that extend to hooves Mammalogy Lecture 9 Locomotion 11 Functional Morphology 1 Again we re going to be resolving force vectors to understand from a biomechanical perspective why evolution has shaped mammal limb bones the way it has We ll take an optimality point of view amp look at morphology from an engineer s perspective II Limbs are a series of levers 7 example forelimb A Structure B Let s look at the forces generated by these muscles and resolve those force vectors C Now we need to define a few terms F0 Out force the force the limb can generate This is the phenotype on which selection will operate Fi In force the force the muscles can generate This is the resultant that we just defined Li Inlever perpendicular distance between the line of action of the Fi and the fulcrum L0 Outlever perpendicular distance between the line of action of the F0 and the fulcrum The relationship between Fi and F0 depends on the lever arm that each force has Torque is the turning force at the fulcrum Inlever Torque Ti LiFi Outlever torque T0 LOF0 D Remember at equilibrium all forces are equal gt T0 Ti This means then that FOL0 Fi Li F0 is the parameter of interest so we solve for F0 F0 LiFiL0 Fi Li L0 We can therefore optimize the force of a limb F0 in two ways 1 Increase Fi gt this is determined by the number of muscle fibers We have a finite space so optimizing F0 by this means is limited 2 Increase Li L0 In terms of mammalian forelimb long olecranon process amp short forearm We do see mammals that appear to optimize F0 in this manner 1 Talpidae mole family Scapanus orarius 2 Dasypodidae Armadillo 3 Geomyidae gopher family Thomomys talpoz39des 4 All the myrmecophagous forms we ve mentioned We might then ask the question why isn t F0 always optimized That is why don t we see a long olecranon process and short forearm in all mammals E Of course the answer is that there s a direct trade off with velocity At equilibrium VoLi ViL0 V0 velocity at the end of the outlever Vi velocity at the end of the inlever So if we optimize the speed at which a lever works V0 Vi LOLi or Vi LoLi Again velocity can be optimized in two ways 1 Increase Vi gt V is the velocity of muscular contraction is physiologically limited 2 Increase LOLi gt Directly opposite optimization of force We expect that limbs that optimize velocity to have a very short olecranon process and a very long forearm We actually see such limbs in Cervids Deer family Odocoz39leus Bovids Cow and goat family Ovis canadensis Equids Horse family Equus caballus Leporids Rabitt and hare family Lepus townsendii Canids Dog family Cam39s latrans Felids Cat family Puma concolor Selection has optimized V0 at the expense of F0 Most mammals have limbs that represent a compromise Generalized limbs have a moderate capacity of generating power and moderate velocity Mammalogy Lecture 12 Reproduction Cyclicty amp Life History Strategies I Cyclicity A In one mammal there is a single reproductive cycle during the life of an individual semelparous 7Antechz39nus 7 a Dasyuirid marsupial mouse B By far most mammals are itreroparous and have more than one cycle per lifetime C Cycles Estrous Cycle Ovarian Cycle 7 production of ova Uterine Cycle 7 preparation of uterus for pregnancy Spermatogenic Cycle 7 production of sperm In general male cycle tends to track the female cycle in species with infrequent estrus but there are interesting exceptions we ll discuss D These cycles respond very differently to pregnancy in Eutherians vs Metatherians In Eutherians the estrous cycle is interrupted between cycles for pregnancy In Metatherians for the most part there is no interruption between cycles amp gestation must occur within a single cycle E Control of Cyclicity Primarily all cycles are under control of the pituitary hormones Very often this cyclicity is regular as is the case in humans Or it actually may be induced amp there are many cues that can induce the pituitary 1 Visual Cues 7 In most species testicles are quiescent for most ofthe year and sperm production ceases The testicles are often housed in the body cavity where the temperature is too high for sperm production In preparation for breeding the testicles descend into the scrotum through the inguinal canal Such testicles are called scrotal In many mammals they are scrotal throughout life Once descended sperm can be produced and the epidydmys and testes swell In some mammals the sight of scrotal testicles actually induces female estrous cycle For example this is the case for many Primates Here the spermatogenic cycle drives the estrous cycle 2 Behavioral Cues may trigger hormonal responses suckling macropodids more detail in a minute copulation felids 3 Environmental cues perceived by any of a variety of senses act on the pituitary and thereby confer seasonality Examples M icrotus montanus Montane vole both males and females become reproductively active in response to a substance 6MBOA that is present in high concentrations in young actively growing plants Young are produced only when adequate food is available Dz39podomys Kangaroo rats are desert rodents that live for several years In particularly dry years there is no seed crop 0 of females become reproductively active Again these environmental cues operate external to cycles to confer seasonality This seasonality is important for two reasons It allows l Breeding when there is sufficient food to fuel postnatal growth of young 2 Sufficient food to fuel lactation for mother This is particularly important because lactation is around twice as expensive as gestation On top of this cyclicity several mechanisms have evolved for optimizing the timing of birth within a cycle 1 Delayed Fertilization Sperm Storage occurs in both males and females Vespertilionid bats 7 In M yotis spermatogenesis ends by late August and males store sperm in the epididymis a spermstorage organ associated with testicles until breeding in late October as the bats congregate at hybemacula Females then store sperm in the uterus for up to three months prior to fertilization in February Allows for partuition birth in spring after about 3 7 4 months when aquatic insects are starting to emerge and become abundant 2 Delayed Development Occurs in a few bats Blastocyst implants but then becomes dormant In Artibeus a phyllostomid the embryo implants in the uterus in mid summer development halts until early winter Partuition occurs at the end of the dry season when fruits are most plentiful 3 Delayed Implantation Common Chiroptera Camivora Xanarthra Artiodactyla Rodentia Insectivora After copulation the fertilized zygote reaches the blastocyst stage and then becomes dormant It remains oating either in the oviduct or uterus and is encased in a protective coat the zona pellucida Development halts After a period of dormancy which may last up to nine months the blastocyst implants and gestation continues May be obligate and always occur eg Ursus americanus May be facultative and occur only when conditions are bad as in many rodents It s been well studied in carnivores and until recently it was thought that delayed implantation evolved several times A recent paper published in Evolution Thom et al 2004 Evolution 58 175 examined delayed implantation in the context of carnivore phylogeny and there appears to have been a single origin in the Camivora and it s just the family Mustelidae in which it has been lost repeatedly Further within mustelids it appears that the taxa that experience greatest seasonality are most likely to retain delayed implantation There is also an association with longevity short lived taxa can less afford to delay reproduction 4 Embryonic Diapause Seen in Macropodids 7 Some folks e g your text lump this with delayed implantation but since macropodid embryos only attach loosely to the endometrium many folks treat this as a fourth mechanism This is facultative it only occurs if there is already a joey in the marsupium A young is born as mentioned there s no interruption in the estrous cycle in marsupials A postpartum estrus occurs Typically another ovum is fertilized while the rst offspring is still very poorly developed and attached to the nipple The suckling of the ISI neonate triggers hormonal suppression of the second blastocyst preventing further cell division and preventing attachment to the endometrium This is called embryonic diapause and can last up to 235 days When the lst joey leaves the pouch hormonal suppression of the second embryo ceases and normal attachment and gestation of the balstocyct occurs Since gestation is so short 30 days the lst joey is still suckling when the younger sib is born Thus adjacent mammae provide milk of different composition The older joey suckles from a nipple that is producing milk of little or no fat whereas the younger joey is suckling from a nipple that is producing milk with very high fat content Mechanism for the switch is unknown Again a postpartum estrous occurs and a third embryo is fertilized Female kangaroos usually have three offspring going at a time An old joey A very young joey An embryo in diapause We often hear that the marsupial mode of reproduction is vastly inferior and primitive realtive to that of eutherians This is referring to the efficiency of transport of maternal nutrients across the placents The situation just described this is actually a very highly derived system that allows essentially a back up embryo to be perpetually available Mammalogy Lecture 1 Introduction to Mammals I In terms of the number of living species mammals are not a particularly diverse group there are only 4629 described species listed in the most recent taxonomic checklist although more have been discovered since For perspective this is just over half the number of bird species However if we look at morphological diversity mammalian diversity is really quite remarkable For example if we just look at size the smallest mammal is Craseonycteris thonglongyai the Bumble bee bat It weighs just under 2 grams basically the weight of a couple of paper clips The largest Balaenoptera musculus the blue whale can weigh up to 200000 Kg that is 200 Million g This represent a size range spanning 8 orders of magnitude In addition these two species represent both ying and marine forms There are also gliding forms saltatorial hopping forms fossorial burrowing forms arboreal forms and forms that specialize on a diet of ants Each of these lifestyles has a suite of traits that are usually associated and we ll learn about these throughout the semester This diversity is especially remarkable when we recognize that all mammals originated from a single common ancestor that is a single ancestral species that live ca 170 million years ago II So we ll spend the semester exploring both the nature and the origin of this diversity but before we move on I think it s a good idea to try to come up with a definition for mammals Short definition hairy milk producing endotherrn that gives birth to live young Like most short answers this one has some problems there are exceptions to each of the terms in the definition Furthermore it39s useless for fossils We ll list mammalian characteristics and contrast each either with other tetrapods or where we can with the condition seen in the earliest ancestors of all mammals A Soft Anatomy Characters Eleven characters 1 Lactogeneic nourish young by producing milk with mammary glands 2 Viviparous exception are monotremes which we ll discuss later 3 Hair Hair is a uniquely derived feature of mammals not found in any other group Structure is well suited to serve as an insulator Cuticular scales cortex medulla 4 Sweat and Sebaceous glands sweat glands evaporative cooling sebaceous glands associated with hair 5 Endothermic That is mammals produce their own heat through metabolic processes 6 Four chambered heart with complete separation of pulmonary and systemic circulation 7 Annucleate Red Blood Cells This provides more space for hemoglobin and greater capacity for carrying oxygen 8 Separate renal artery and vein rather than a renal portal system 9 Muscular Diaphragm used in respiration 10 Facial muscles This allows for facial expression and is important in communication These facial muscles are derived from ancestral constrictor coli which itself evolved from interhyoideus 11 Expanded cerebral portion of brain particular portion called dorsal pallium B Hard Anatomy Skeletal Characters Cranial Eight cranial characters 1 Double occipital condyle the point of articulation between skull and vertebral column The ancestral condition is a single condyle similar to that seen in a modern alligator skull 2 AtlasAxis Complex modifications of the first two cervical or neck vertebrae When mammals rotate head atlas rotates on shaft of axis 3 Tympanic bone is present that supports the tympanum or eardrum This is derived from an ancestral lower jaw bone called the angular In many species this forms an auditory bulla 4 Three ear ossicles transmit sound waves from the ear drum or tympanum to inner ear malleus articular ancestral jaw joint incus quadrate ancestral jaw joint stapes stapes or columella U1 Single pair of bones in lower jaw or mandible the dentary Since it s the only bone it participates in the jaw joint This is a key paleontological character as we ll see later 0 Single opening into nasal cavity we have two nostrils but one bony opening External Nares ancestrally there were two I Secondary Palate A solid shield of bone separating nasal and oral cavities Ancestrally external nares opened into oral cavity Ventral and medial extensions of palatine bones maxillae and premaxillae separate the nasal cavity from oral cavity This allows mammals to breathe while processing food 8 Respiratory turbinates These convoluted bones in the nasal cavity are thought to be critical for endothermy and we ll talk about their role in mitigating respiratory water loss Teeth Five dental characters 1 Lack palatal teeth teeth are restricted to jaw margins 2 Diphyodont At most there are two generations of teeth This contrasts with monophyodont and polyphyodont 3 Thecodont Teeth are rooted in a socket as opposed to acrodont or pleurodont 4 Heterodont Different teeth have different shapes and different functions as opposed to homodont seen in alligator 5 Multicuspate Teeth have lots of cusps or bumps contrast with unicuspate Axial Skeleton 2 axial characters 1 Extreme regionalization of vertebral column cervical region neck vertebrae almost always 7 some groups with 9 thoracic region chest region 12 or 13 lumbar region lower back variable number sacral region associated with the pelvis caudal region associated with the tail 2 Ribs are restricted to thoracic vertebrae Appendicular Skeleton Four charactes associate with the limbs 1 Limb bones have epiphyses Bony caps at either end that are separated from the shaft by cartilage that ossifies during ontogeny This permits a great deal of stress at joints 2 Calcaneum There is a heel bone where Achilles tendon inserts This provides a great deal of leverage for extension of the foot 3 Reduction in the of bones in limb girdles the point of attachment of limbs to axial skeleton pectoral girdle scapula plus clavicle lack anterior and posterior coracoids as well as an intercalvicle The exception is monotremes pelvic girdle ileum ishcium pubis fused into the pelvic bone 4 Limbs rotate under body contrast with lizards for example which exhibit a condition similar to the ancestral condition C The presence of these characters in mammals represents really a sweeping set of changes relative to those present in ancestors We ll go through that a bit later Mammalogy Lecture 4A Metatherian Diversity 1 Therians under our classi cation rst evolved during the Cretaceous Remember that dinosaurs were still around so ancestral therians were very small 11 Metatherians Marsupials are a monophyletic group Older classi cations treat Metatherians as a single order Marsupiala most folks now recognize 7 orders Marsupials probably evolved in North America or Asia in during the Cretaceous there are fossils in Texas and a recent nd from China dispersed to S America where they diversi ed across Antarctica and into Australia and went extinct in N America and later 3 MYA reinvaded N America Currently there are three South American groups and four Australian groups A South American Groups Three Orders 1 O Didelphimorphia New World Opossums Primarily South American one genus has reinvaded North America Single Family F Didelphidae 15 G 63 S Tribosphenic molars gt Omnivorous Hallux or big toe is opposable 5 upper incisors 4 lower incisors polyprotodont Didelphis American opossum There is a record from Idaho but IFampG does not consider this to be an Idaho mammal Marmosa mouse opossum Northern Mexico through southern S America These have a prehensile tail They lack a marsupium but young attach securely to nipples 2 O Paucituberculata shrew opossums F Caenolestidae with 3 G and 5 S Have a very enlarged medial pair of lower incisors and several smaller pairs Diprotodont No marsupium Paired sperm seen also in Didelphidae C aenolestes occur in high elevation Andean forests near tree line 3 O Microbiotheria monotypic Single Family Genus and Species F Microbiotheriidae Dromiciops Common name Montio del monte or Colo colo Nocturnal arboreal insectivorous Polyprotodont B Australian Groups Four Orders Until recently it was thought that these represented a monophyletic group and that there was only a single invasion into Australia Several papers have suggested that one Australian group which includes kangaroos is more closely related to Microbiotheria than to any other group of Australian marsupials This would imply either two independent dispersal events to Australia or a secondary dispersal of Microbiotheria back into S America 1 O Dasyuromorphia Three living families 15 Genera 61 species F Dasyuridae marsupial mice and rats 43 incisors polyprotodont tribosphenic molars Sarcophilus tasmanian devil Nocturnal scavengers now present only in Tasmania F Thylacinidae tasmanian wolf monotypic Thylacinus cynocephalus considered to be extinct Last specimen was taken in 1930 last known was a zoo animal that died in 1933 In 1960 there was a track reported in western Tasmania There continue to be unverified sightings but in all likelihood these are extinct F Myrmecobiidae Numbat or Bandedanteater M yrmecobius Diurnal and myrmecophagous eats ants Marsupium is absent Found in eucalyptus woodlands in SW Australia Myrmecphagous adaptations tongue is long and extendible Saliva glands produce viscous sticky saliva long rostrum wdelicate dentary reduced or absent teeth front limbs modi ed for digging 2 O Notoryctemorphia monotypic marsupial moles F Notoryctidae Notoryctes Rare animal occurs in desert NW and SC Australia True moles don t occur in deserts Nose has a cornified shield Our first example of a fossorial mammal adapted for burrowing Small eyes and small pinnae Fur is velvety doesn t lie in one direction Fusiform body with a short tail Forelimbs modi ed for digging Claws on 3rd amp 43911 digit are enlarged and the others are reduced Teeth neither polyprotodont nor diprotodont characteristics of both 34 incisors Not as fossorial adapted for burrowing as other moles While they are fossorial burrows are not deep only a few cm below sand burrows are ephemeral not long lasting and the animals move over surface frequently 3 O Peramelemorphia bandicoots two families we ll only mention one Tribosphenic molars forelimb is shorter than hind limb F Peramelidae widespread in Australia 14 Genera and 21 species 2nd amp 3rd digits are syndactylous That is they have a single sheath of skin Have a eutherialike placenta independently evolved polyprotodont M acrotis Rabbiteared bandicoot 4 O Diprotodontia Diprotodont marsupials Two front teeth Most forms have single pair of upper and lower incisors when 2nd or 3rd pair is present these are usually reduced Many forms have some type of syndactyly the bones of two or more digits enclosed in a single sheath of skin It s this order that is hypothesized is sister group to Microbiotheria 10 Families in the order we ll mention a few of these families F Phalangeridae Phalangers 6 Genera 18 species Found in forests of Australia and New Guinea Adapted for arboreal life prehensile tail naked ventral surface Welldeveloped marsupium Phalanger spilosoma spotted cuscus gt opportunistic feeder Serve as an important food source for Aborigines of Australia F Petauridae Gliders 3 Genera 10 species Found in Northern Australia and New Guinea Petaurus breviceps Sugar glider Rectangular gliding membrane between ankles and wrists Glide up to 50 M many ways similar to ying squirrels Feet have an opposable halluX F Phascolarctidae Koala monotypic Phascolarctus restricted to eucalyptus feed on only 12 species Endangered and fully protected Typically have a strong eucalyptus order lst and 2quotd digits are opposable in the hand foot 2quotd and 3rd digits are syndactylous Our rst example of an arboreal foliavore low quality food eat almost constantly while awake sleep to digest low metabolism heterothermic dense fur to retain body heat F Vombatidae wombats 2 Genera 3 species herbivorous construct burrows and these are clustered into colonies that can be seen from satellites though colonies they are solitary in that each individual has its own burrow and they don t interact much except during mating season Lasiorhinus Hairynosed wombat F Macropodidae Kangaroos and Wallabies ll Genera53 species Widespread in Australia New Guinea and Indonesian Islands All grazers and browsers Multichambered stomachs that function in a manner similar to those of deer and cattle All are saltatorial adapted for bipedal hopping Syndactylous 2nd amp 3rd digits are reduced and sheathed together 4th digit is very enlarged and strong Tail is very thick at the base and used for balance There are typical plains grazers Macropus rufus Red kangaroo these get up to 90 kg very gregarious mobs of 200 common may reach 1500 There are arboreal forms Dendrolagus tree kangaroos NE Australia New Guinea and Indonesia incredibly agile leap from ground up into trees leap down from as high as 18M tail is not prehensile but used extensively as a brace There are rock dwelling forms Petrogale Rock wallaby gt introduced onto Oahu in the 1920 s and there still is a population of around 50 indiViduals http wwwetymonlinecomindexphp termLaljn Lecture 8 e Locomotion Flign A lnseets e membranbus sheets ufchmn suppuned by yens B Ptemsaurs e 5km membrane Suppuned by smgle mgrt Am C Blrds e feathers suppuned byhmb bunes andreduced an metaeapral and dlgt Bats e 5km membrane suppuned by the 2m Lhmugh 4th mgrts ll Basre aspeets ufaemdynamlcs A The prbblem mvulves uvercummg the fume bfgrayrty Dr gmerz ngli alrfml They are asymmetmern crussrsecnun Ltt t rehes un Lammar Flaw parallel muvement uf atr streams alrfml amyes atthetrarhng edge atthe same tame sh arr aws faster aemss the tap than buttbm bfthe mrfml rfthere ls aeuryature B Bernmllli39s Thenran Pls atrpressure Cls a ebnstant tits the denslty bfatr and Vls veluclty ThrFr m hlhr l w muvmg faster aemss thetbp bfthe wrngresults m luwer arr pressure un thewrng beluw than abuve Thls dlfferennal m pressure ls ealleahtt and when Lhangmtude ufll ls greater thanthe fume ufgavlty aetang unthe abject argntrs aehteyea Lt Puma ernnu The magnitude of lift is dependent on the differential in V the speed with which air passes along airfoil This differential increases with ight speed so it s more dif cult to maintain ight at low speeds III This is particularly important to ight in bats because for the most part they re slow iers There is variation in ight speed Myotis luci gus 20 mph Eptesicus fuscus up to 40 mph T adarida brasiliensis up to 60 mph But most bats are slow iers more like Myotis and slow ying is the primitive condition A Bats deal with generating lift at low ight speeds in a number of ways 1 One way around this is to increase the curvature of the upper surface 7 camber The nature of the airfoil in bats is a little different than a plane it s a thin airfoil and the shape can be modi ed As increase curvature 9 increase the differential in speed of air ow across upper surface relative to lower surface 9 increase lift 2 Another is to increase the angle of attack an airfoil coming at an air stream edgeon generates less lift than one that is inclined slightly Again this is because of the difference in distance that the split air stream travels 3 A third relates to wing size and shape a Wing loading Body weight surface area In general the lower the wing loading the easier it is to overcome the force of gravity Bats typically have low wing loadings Body Weight Surface Area Wing Load House wren 110 g 484 cmz 024 g cmz Glossophaga 106 g 993 cmz 011 g cmz Myotis 42 g 676 cmz 006 g cmz b Aspect ratio shape of the wing length width Low aspect ratio wings are better for slow maneuverable ight Remember Glossophaga is a phyllostomid bat that eats fruit and forage in forests High aspect ratio wings are better for rapid ight T adarida is a molossid bat that you saw in the lab that forages in the open Page 203 in Text has good illustration of these two wings 4 Another is a phenomenon called leadingedge aps At low ight speeds there is a tendency for laminar ow to break down The next time you re on a plane check out the front of the wings on takeoff Leadingedge aps promote laminar ow at low speeds Bats do all of these things Slow yers tend to have higher angles of attack higher camber wings and larger surface area wings with low aspect ratio B Parts of a bat wing contribute differently to ight Propatagium between shoulder and wrist Dactylopatagium breVis between first and second digits D minus between second and third D longus between third and fourth D latus between 4th and 5th Plagiopatagium between 5th digit and the hind limb Uropatagium between the two hind limbs IV So far we Ve only been talking about lift but unlike in an aircraft the wing also has to generate thrust A Wingbeat cycle 1 Downstroke is the power stroke It is powered by three muscles pectoralis subscapularis serratus 2 One part of the wing in particular has been implicated in generating thrust Dactylopatagium longus This is not well braced so during the downstroke this segment of the wing lags behind the rest of the wing As the downstroke nishes the front of the D longus is much lower than the back this has the effect of forcing air backwards This is what generates thrust It is also likely that the D arm has some thrust generating function as well 3 The function of the other portions of the wing during the downstroke Propatagium D brevis and D minus serve as leading edge aps Plagiopatagiun is actually very wellsupported by the stronglybraced 5th digit and the hind limb This allows it to maintain both its camber and angle of attack throughout the downstroke and therefore it is the primary lift generator The Uropatagium is not present in many bats but it serves for steering and in many insectivorous forms is used as a net to catch insects in while ying 4 The upstroke is the recovery stroke in most forms The wing is partially closed There are muscles that function during the upstroke but these are greatly assisted by air pressure so to some degree the upstroke is passive There s a great deal of variation in the manner in which the upstroke is stopped Shoulderlocking mechanism is formed by the greater tuberosity of the humerus In mollossids the really fast iers the situation is as I ve drawn on the board In vespertilionids the greater tuberosity is also well developed and acts as a locking mechanism In phyllostomids there is only a moderate expansion of the greater tuberosity There are a few groups such as the family Embalonuiidae with no expansion of the greater tuberosity and no shoulder locking mechanism The upstroke is stopped entirely by muscular contraction V Some other skeletal adaptations to ight A Many bats have a keeled sternum manubiium the rst segment B Some have aXial skeleton modi cations Natalidae very rigid aXial skeleton that is formed by l Compressed thoracic vertebrae not fused but very tightly interconnecting 2 Fused sacral vertebrae and fused lumbar vertebrae Mammalogy Lecture 12B Reproduction Cyclicty amp Life History Strategies 11 Life History and Reproduction Within any group there is really wide variation in reproduction but there are a few general trends discernible A General Trends Relating to Body Size Many of these trends show weak correlation They have a good deal of scatter but trends are still apparent 1 In general the total number of offspring per lifetime tends to decrease with increasing body size This holds true both within and among groups Were we to do something similar across a broader taxonomic array we would still see at trend but there would be more scatter 2 Small mammals tend to have higher basal metabolic rates than large mammals SV and also tend to have very sh01t life spans This relates to reproductive strategies in several ways a Small mammals tend to have large litters 7 up to 15 pups per litter in Microtus b Small mammals typically have rather short gestation times among eutheria For example some arvicolines have gestation periods as sh01t as 21 days c When the young are born they tend to be rather altricial essentially helpless blind deaf naked d Typically have a very high post natal growth rate Reach a given percentage of adult body weight faster than do large mammals especially true when subjected to seasonality The effect of seasonality on rate of postnatal growth rate is see in M yotis For species of similar body size postpartum growth rates are higher in temperate forms that need to store fat for hibernation than for species in the tropics and subtropics D Reach reproductive age very quickly Microtus can reach sexual maturity at an age of 15 days So the next generation is ready to breed 36 days after conception basically 5 weeks 10 generations per year All of these tendencies fall into a category that MacArthur dubbed r selected These traits optimize genetic contribution to subsequent generation by maximizing the quantity of offspring produced f The extreme of rselection in mammals is the marsupial mice Antechinus which as we mentioned are semelparous single reproductive cycle lifetime 3 Large mammals tend to have lower BMR and tend to have much longer lives a Typically have relatively long estrous cycles 22 months in Elephas b Litter size is typically one or two rarely much higher than 3 c Young tend to be more precocial especially in cetartiodactyls and perissodactyls d Counterintuitively lactation may be prolonged and the precocial young of large mammals may grow much more slowly e These traits are often considered k selected Optimize genetic contribution to future generations by producing fewer offspring but investing more in each one r vs kselection is a gross over generalization and it s never wholly accurate to call a species rselected and expect that all of its characteristics to fit what we would expect of an r or k selected form However it s still a useful concept in addressing reproductive traits B Exceptions Although the relationships described above hold in general there are many interesting exceptions l Microchiroptera small mammals reproduction is more like that of a large mammal only 1 or 2 young annually have very low metabolic rates for their size Are actually heterothermic first reproduction is at 18 months of age really odd for small mammals in that they can have very long life spans Some little brown bats M yotz39s lucz39fugus have been captured 30 or more years after banding 2 Macroscelidids Elephant shrews Elephantulus are small but bear only one or two precocial young after a rather long gestation period These are ground nesters and rely on alertness and locomotion as defense against predation 3 Hystricognath rodents have much longer gestations than their sciurognath counterparts Tucotuco Ctenomys is the South American ecological equivalent of North American Thomomys pocket gophers both bear 4 altricial young but Ctenomys has 3X longer gestation In general large and small trends don t hold up well in hystricognaths because both large and small species may produce altricial or precocial young after a long gestation time 4 Marine camivorans Pinnipeds very large but have incredibly rapid postnatal growth rates Elephant Seals M irounga huge may double their weight in 10 days This rapid growth is necessary for pups to survive first winter at sea III Advantages and Disadvantages of AltricialPrecocial Young from Eisenberg 1981 Distillation If risk of neonatal mortality is high the production of altricial young will be favored If the risk of neonatal mortality is low the production of precocial young will be favored A Seasonality and mortality 1 If seasonality is not predictable the production of altricial young will be advantageous As altricial young reach weaning sooner energetically expensive lactation is lessened overall cost ofa single litter is lessened Not as big a loss ifa single litter is lost Recycling of nutrients If conditions become adverse Early 7 fetuses may be resorbed in utero Later in Pregnancy 7 litter aborted and recycled orally or by miscarrying and eating the fetuses After birth 7 eat young Can also be accomplished by killing and eating neonates This also allows for changing the sex ratio in polygynous species This is not an option for large animals that bear precocial young especially ungulates which lack the required masticatory apparatus 2 If seasonality is predictable mortality will be low and the production of precocial young will be favored Large animals can overcome predictable shortages food by storage of energy so the daily drain caused by lactation may be less This then offsets the overall increase in energy needed for the extended lactation periods required by slow growing precocial young B Predation Predator avoidance is necessarily passive in species with altricial neonates and is active and assisted by the parent in species with precocial young 1 If predation is high then altricial young are favored gt Optimize the total of offspring because many will be eaten 2 If predation is low precocial young are favored gt optimize the chance of each offspring s survival Mammalogy Lecture 2 Origin of Mammals I There are three major living extant groups of mammals A Monotremes egg laying mammals B Metatherians marsupial mammals C Eutherians Placental mammals These are related by the following evolutionary tree or phylogeny Monotremes Metatherians Marsupials Eutherians Placentals Node Divergence Event Branch Common Ancestor Marsupials and placentals share an ancestor not shared by monotremes II A In order to understand the origin of mammals we have to look farther back into the Paleozoic 350 MYA and look at relationships among the tetrapod vertebrates So we ll start by going deeper in time and work our way back up to this level in the phylogeny Amphibians Mammals Turtles Squamates Crocodylians Dinol Birds DinoZ Stem Reptiles Captorhino morph Amnion Transition to land We can mark evolutionary changes along this phylogeny the evolution of limbs the evolution of the amnion etc It s this lineage labeled Synapsida that we ll examine in order to understand the origin of mammals We need to understand the situation just prior to this in the stem reptiles the ancestors to mammals birds turtles and other reptiles Captorhinomorphs B In the Carboniferous ca 350 MYBP the captorhinomorphs evolved and the synapsid lineage diverged from the stem reptiles 30 MY later 320 MYA and it s this lineage that will eventually lead the modern mammals Synapsid together arch describes a skull condition that is unique to this lineage The word synapsid is also used to refer to the group of organisms that exhibit this condition Anapsids Lower jaw musculature jaw adductors anchored to inside of this shield of bone Still present in some turtles Modern tetrapod groups have different modifications of this ancestral anapsid condition Captorhinomorphs were anapsid has no temporal fenestra Early synapsids Pelycosaurs evolved an opening in this shield temporal fenestra This provides a much more solid anchor for the lower jaw musculature In synapsids the fenestra opens below the suture between the squamosal and postorbital bones In later synapsids both the temporal fenestra and the braincase expand greatly and the original dermal shield becomes very reduced This is the situation in modern mammals C Synapsid Phylogeny quotPelycosaursu Early The rapsids 1 Pelycosaurs aka nontherapsid synapsids Arose in the Early Permian prior to the diversi cation of dinosaurs ca 320 MYA In the mid 1980 s we thought these were entirely carnivorous only a single lineage had been discovered This is what I learned and is based primarily on the frequently represented genus Dimetrodon Since then early synapsid fossils have been discovered that were clearly herbivorous and others that were insectivorous it s clear that they were much more diverse than we previously thought and there were multiple lineages For example there was much more variation in both diet amp activity than we once thought and there were also both herbivorous amp insectivorous pelycosaurs Still though they were all rather large about 3M long They had a large dorsal sail that probably was thermoregulatory some postulate it was used in sexual selection They had many ancestral characters They were only weakly heterodont They had only a small temporal fenestra through which only little of the jaw adductors passed The dentary was not greatly enlarged with several post dentary bones in the mandible The jaw joint was formed by the quadrate bone upper and the articular bone lower They had no secondary palate nares opened into fort of oral cavity They had a single occipital condyle 2 Therapsids By the Middle Permian ca 265 MYA a separate lineage became dominant These are known as Therapsids sometimes called advanced synapsids Early therapsids were actually quite large gt 35 meters The therapsids were very diverse in the mid Permian There were lots of groups herbivores carnivores etc All were rather active This was prior to the origin of dinosaurs amp therapsids were the dominant terrestrial veretbrates They exhibited an enlarged temporal fenestra There was a partial secondary palate we see gradual evolution of the palate It s in one particular therapsid lineage that we see the sweeping sets of changes in skull and jaw morphology which we ll go through in more detail later At the end of the Permian there was a mass extinction 90 of all species including most of the therapsids went extinct Permo Triassic extinction 3 Cynodonts advanced therapsids arose in the very late Permian and survived the mass extinction In this lineage we see the very gradual evolution of many mammalian characters we ve already discussed with tons of transitional fossils It s here that we first see a complete secondary palate Two occipital condyles are present There is a gradual enlargement of the dentary and shrinking of post dentary bones There is a vast expansion of the temporal fenestra amp braincase Strongly heterodont dentition arises It s almost certain that cynodonts interacted with dinosaurs directly It may well have been that cynodonts were preyed upon rather heavily by dinosaurs which diversified and became dominant in the early Triassic For whatever reason competition predation or something else by the late Triassic the cynodonts were nearly all small and inconspicuous Classic thinking has been that cynodonts represent the ancestral stock from which modern mammals evolved and the extinction of the dinosaurs at the end of the Cretaceous permitted the radiation of modern mammals D So there are several issues that we ll be interested in examining the origin of mammals 1 What are the groups of cynodonts and how are they related 2 Which groups were Mammals 3 Why and how did so many characters evolve We ll start examining these issues by looking at cynodont phylogeny we won t worry about all the groups just those that contribute to our understanding of mammals Cymnlam Phylngunv au Origin ol Mamumls n m i a rvltnmrmwllm mm an Cyuwmm At this point then we get to the second issue how do we classify these fossils That is which ones were mammals The traditional paleontological approach has been to look for key characters if the animal has this character gt we can call it mammal For a while when the fossil record was really spotty this worked well There were no transitional forms and the dentarysquamosal jaw articulation was the key character If a fossil had a dentarysquamosal articulation gt Mammal If it had a quadratearticular jaw joint gt reptile When this was the approach Morganucodontids were the first mammals Sinocodn has a D S jaw joint but wasn t discovered until 1975 Problem arose when intermediate forms were found synapsid evolution represents a continuum Probainognathus both jaw joints Diarthognathus both jaw joints So paleonotlogists responded that we can t use a single key character we need to use a suite of characters This is the approach taken by Feldhamer et al 1 D Sjaw joint 2 Strongly heterodont dentition 3 Molar surfaces complex with wear facets Occlusion 4 Alternate side chewing implying complex jaw musculature 5 Well developed inner ear region 6 Small 7 Axial skeletal characters dorso ventral flexion placement of ribs etc So by this approach if a fossil has most or all of these characters it was called a mammal It s no surprise that this approach led to application of the name Mammalia at the Morganucodontid node the set of characters were chosen by those who already considered Morganucodontids the first mammals Both of these two approaches based on key character and based on a suite of characters represents what we call a gradebased definition That is we have some concept of what constitutes a mammal and if some organism achieves a certain grade of development we can call it a mammal Problems with a gradebased approach Because we have really gradual evolution represented in these fossils and there are lots of transitional fossils it s really difficult and very arbitrary to assign a cut off point based on achievement of some perceived critical mammalian grade Many of these characters evolve at a lot of places on the phylogeny amp we could have mammals evolving at various places D S jaw joint Heterodont dentition Size So using either grade based approach is potentially problematic We re really talking about calssification here so in order to address these problems we need to think about What we require of our classi cations 1 Classification must reflect evolutionary history What this means is that we only want to its descendents Use the Reptile example recognize monophyletic groups Monophyletic group represents and ancestor plus all of 2 Classifications should be stable that is they shouldn t be changing all the time To some degree these to conflict When they do evolutionary history has priority This leads to the second approach cladebased approach clade is a monophyletic group This has the advantage of basing the classification on the phylogeny rather than some arbitrary set of characters About 15 years ago a new wave of mammologists paleontologists decided to change the approach amp restrict Mammalia to the most recent common ancestor of all living mammals To me there s no doubt that a clade based approach is a more appropriate approach But restricting Mammalia in this way would leads to instability So for our purposes we ll use apply the clade based definition to the Morganucodontid node For classification then the facts that heterodont dentition evolved several times that the D S jaw articulation evolved at least twice that a secondary palate evolved several times independently don t matter Any newly discovered fossil that shares a common ancestor with morganucodontids is a mammal This is arbitrary but objective and based on phylogenetics analysis We can address the last question what were the forces that lead to the evolution of these characters only by inference That is we can propose hypotheses and choose that which we deem to be most plausible given the available evidence E The SizeRefugium HypothesisThere are several elements of this hypothesis Much of this rests on the physical law relating SV with body sizeInverse relationship increase body size gt decrease SN and vice versa 1 Early therapsids were relatively large ectotherms Initial selection for large body size because of size low SV gt They had large thermal inertia once warm they took a long time to cool and experienced a fairly constant body temp This is called gigantothermy They were homeotherms This is consistent with living large ectotherms like leatherback turtles Under this hypothesis therapsids became physiologically adapted to a high and constant body temperature over the 100 MY that they were large 2 In the Triassic dinosaurs radiated and became dominant so under this hypothesis there would have been selection for smaller size to escape competition andor predation This is where the name of the hypothesis comes from 3 But as size decreases thermal inertia is lost and heat loss increases Small objects lose heat faster than do large objects If therapsids were already constrained for homeothermy selection would have favored animals with the ability to produce their own heat There would have been selection for endothermy Partial endothermy is pretty common in vertebrates 4 Once endothermy had evolved there are a number of far reaching implications A Energy Requirements An endotherm burns calories to maintain body temperature and requires ca 10X energy as a similar sized ectotherm Selection favored i Increased efficiency of food processing Complex amp specialized dentition with precise contact between upper and lower teeth Specialized jaw musculature 9 evolution of a new muscle the masseter Formation of secondary palate ii Increased cardiopulmonary efficiency Extrusion of nuclei from Red blood cells Increase carrying capacity for O2 in blood Separation of oxygenated blood from deoxygenated blood and evolution of 4 chambered heart More efficient breathing restriction of ribs to thoracic vertebrae and muscular diaphragm Respiratory turbinates recover water lost with increased respiration B Behavioral Implications Because endotherms can generate own heat they can be active on cold nights Endothermy permitted nocturnality Selection favored i Hair for insulation ii Development of olfactory and auditory capabilities So under this hypothesis the evolution of endothermy generated the selective forces that favored most of the traits we consider to be mammalian traits Throughout Jurassic and Cretaceous these mammal groups remained very small and inconspicuous The classic thinking has been that the extinction of the dinosaurs at the end of the Cretaceous allowed for the radiation of mammals and the diversity that we see today to evolve Mammalogy Lecture 13 Social Behavior 1 Social interactions are ubiquitous in mammalian biology Even the most solitary species have bouts of social behavior at least twice throughout the course of the lifetime Once at nursing because all mammals lactate Once at breeding because all mammals reproduce sexually Because the social life of all mammals begins with nursing E O Wilson has postulated that lactation is the fundamental basis of all social behavior in mammals and that all other social relationships are derivatives of motheroffspring relationship However we ll see that much of mammalian social behavior is also tied to reproduction and mating systems as well as other aspects of a species biology II There are at least two different criteria that we could use to define a society A Communication Stewart Altman Primatologist Aggregation of intercommunicating conspecifics bounded by lower frequency of communication B Space John Eisenberg No explicit definition but Eisenberg characterizes societies with regard to how space is partitioned l Colonial social systems Each individual has it s own territory 2 Communal social systems Individuals within each society share the space 3 Dispersed social systems No overlap in ranges and individuals interact only at territorial boundaries 111 Most mammalogists agree that there are several degrees of sociality We ll discuss 5 A Asocial Minimal contact usually marked by aggression Both males and females defend territories Shortterm pairbonds may develop seasonally for breeding usually with 39 39 quot after r 39 quot Females typically force young away after weaning Lynx rufus Bobcat Puma concolor Cougar Geomyids Pocket gophers Thomomys 7 Their habitat is really patchy so they tend to be clustered but are actually very asocial B Simple Aggregations Groups of individuals with no real cohesion Not necessarily centered around reproduction maybe just clumped resources Short term and seasonal High turnover of individuals amp group membership is uid Many species of small antelope Bovidae aggregate around watering holes C Reproductive Social Units Solely together for reproduction Form for the purpose of reproduction males and females may form pair bonds Pair bonds may last just the breeding season or may last for life Monogamous forms may be facultative at low density they re only likely to find one mate or may be obligate Female offspring may stay with mother past weaning Peromyscus californicus D Simple Social Systems Groups are persistent and stable Ordered hierarchy of dominance N0 division of labor Groups may be unisexual or all of the same age Examples Bat nursery colonies Myotz39s and many other bats females roost together while nursing in the summer time Males tend to roost in several smaller colonies near but separate from females Equus burchelli Male often assisted by a subadult defends a harem of females year round E Complex Social Systems Groups are stable amp membership tends to span generations Ordered dominance hierarchy Complex within group communication Division of labor Pair bonds are persistent 1 Monogamous family groups a single reproductive pair nonreproductive individuals Canids especially Cam39s lupus Primates Homo Cetaceans 2 Polygamous family groups usually polygynous single vigilant male with a harem of females plus offspring Baboons Papio Howler Monkeys 7Alouatta C allithrix jacchus whitetuftedear marmoset is one example of a polyandrous species Two males to one female mating 7 equal 3 Eusocial systems queen single reproductive female and castes including sterile workers Naked mole rat Bathyergid genus H eterocephalus is a hystricognathous rodent in the family Bathyergidae It s the only mammal in fact the only vertebrate known to exhibit eusocial behavior Occur in colonies of up to 40 individuals Three castes defined by maximum adult body size Frequent workers 7 smallest amp range from 2530g 7 do the majority of the burrowing work foraging Infrequent workers 7 intermediate size 35 g 7 do a little of the burrowing work Nonworkers 7 4045 grams 7 Don t burrow at all 7 Don t forage but are fed by frequent workers 7 Take care of young Single breeding female queen and she actually seems to suppress the ovarian activities of other females phermonally All males are fertile that is produce sperm but only the large nonworkers mate Once again these categories are generalizations and there is a continuum of social behavior in mammals from asocial at one end to eusocial at the other IV Evolution of Social Behavior CostBenefit Ratio A Costs of group living 1 Increased conspicuousness crypsis is not an available means of predator avoidance 2 Increased intraspecific competition for food and mates especially true in cases with dominance hierarchies 3 Increased risk of parasitismdiseases 4 Increased potential for inbreeding and potential inbreeding depression DJ Benefits of group living 1 Sel sh herd phenomenon The risk of predation incurred by any single individual may be smaller in a herd than for solitary prey species Cooperative predator defense possible Musk ox Ovibos moschatus where adults form a ring around young Cooperative hunting Cam39s lupus Panthera leo Information sharing possible and cultural inheritance In some primates learned behavior may be passed between generations Division of labor possible N 5 V39 The costbenefit ratio will determine whether or not group living will evolve This will vary between species obviously and we ll talk about some examples This also may vary between genders with a species Male Dispersal Much has made in the sociobiology literature of the cheap nature of male gametes relative to the costly nature of female gametes This explains why polygyny is so much more common than polyandry Mate choice is usually driven by females Manifestations of sexual selection are usually seen in males eg antlers But it also may explain the predominant pattern of female philopatry and male dispersal in mammals Females are typically philopatric They reproduce in the same population as they were born It s a site that s proven to be adequate Males tend to disperse between populations and seek new suitable habitat C Alarm Calls in Spermophilus beldingi Series of studies by Paul Sherman A very wellstudies case of altruistic behavior behavior that enhances the tness of other individuals at the expense of your own tness is Spermophilus beldz39ngi These squirrels occur in mountain grasslands and they form breeding colonies As predators approach they ll give alarm calls and the rest of the colony will ee into burrows This really does appear to be altruistic behavior because Sherman has been able to show that there is a higher probability of predation on call givers that is the call attracts attention to the giver In order to understand this we need to understand a little about Kin Selection and Inclusive Fitness Our own offspring share on average 50 of our genes So do our sibling on average Their offspring share 50 of their genes Thus our nieces and nephews share 25 of our genes This is the same as our grandchildren So one way to optimize our genetic contribution to subsequent generations is to act in a manner that increases the success of our relatives Thus behaviors that increase the chance of success of relatives may be favored even if those behaviors reduce the tness of the individual In the case of Spermophilus beldz39ngz39 females are philopatric that is they don t disperse A female is likely to reproduce with the same colony as she was born in Males on the other hand are disperse among colonies and are therefore not likely to be related to colony members Kin selection theory would predict that only females give alarm calls because only females will increase their inclusive tness by doing so This is exactly what the squirrels do Furthermore kin selection theory predicts that in colonies where females are more closely related genetically there is a greater tendency to give alarm calls That is females must be able to discern relatives from nonrelatives This was actually born out by experiments Females call less frequently when there are fewer close relatives in the colony D Examine the variation in benefits received by social behavior across species by looking at carnivores Most Camivores are solitary or asocial Presume that this is the ancestral condition for the order All ursids are asocial Many other families are primarily asocial Within each of these families sociality has evolved Procyonids Mustelids Herpestids mongooses Felids Hyaenids Canids situation is very exible in coyotes Cam39s latrans are social when there is much carrion and asocial when feeding on rodents Cam39s lupus family groups gt cooperative hunting Vulpes vulpes Cooperative hunting pairs Felids Panthera leo up to 4 breeding females several nonbreeding females and 2 males may or may not be related females hunt and are related some males will forego breeding if they are related to the breeding males satellite males belong to no pride and attempt sneak copulations Hyaenids Crocutta crocutta rather large groups odf up to 10 both males and females suggestion that thee group form to defend kills from lions Mustelids Males meles Live in communal dens of 10 s of animals Interesting is that these animlas forage alone rather omnivorous Build a huge burrow system that is used for several generations Clans family groups efense of territory Herpestids H elogale Dwarf mongoose Very complex social system There are nonreproductive males and females only a single breeding pair Forage independently Do see coopoerative predator defense See alarm calls given and some division of labor A series of hypotheses have been erected to explain this repeated evolution of social behavior in carnivorans Focus on cooperative hunting predator defense or defense of kills Benefits really vary across species and no hypothesis that emphasizes only a single aspect of sociality can provide a general explanation but there may be a general initial catalyst D W MacDonald gt Resource Dispersion Hypothesis Common set of starting conditions Basic territoriality Individuals defend the smallest area that will support them in a bad year Size of the territory depends on dispersion of resources Key is that it s usually not a bad year and resources are readily available each resource patch may support more than one individual Most of the time there is a very low cost to group formation gt benefits outweigh the costs Type of social system that will evolve then depends on the ecology of the particular organism Mammalogy Lecture 7 Evolution of Lower Jaw and Middle Ear I To begin let s examine brie y the end point that is modern mammalian ears Inner Ear cochlea contains sensory cells for hearing and balance lies embedded in the braincase Middle Ear connects the outside world to the inner ear amp contains the ossicles functions as a transducer transmits ground and air vibrations to the inner ear is surrounded by the auditory bulla in many eutherians Outer Ear cartilaginous pinna 11 We re going to examine the evolution of the ear ossicles and this is intimately tied to the evolution of the lower jaw in mammals This evolution is integral to mammalian biology 7 feeding diversitydietary specialization To me this is one of the most remarkable examples of some common features of evolution 1 Gradualism 9 Evolution is often very gradual Change from one morphology to another very different morphology occurs through a series of intermediates This documents transitional forms 2 Modification of existing structures 9 For the most part evolution modifies what s already there and when new structures arise they split off existing structures masseter 3 Constraints 9 Organisms are integrated wholes and changes to a particular system don t occur in a vacuum characters are nonindependent and functions change over time III In addition we ll begin to explore functional morphology Analyze biological structures using principles of physics We ll restrict our attention to very simple principles 1 In equilibrium any force that is being exerted is resisted by an equal and opposite force 2 We ll learn a little about force vectors VI Ancestral Condition Pelycosaurs early synapsids 1 Remember Solid skull roof with very small temporal fenestra 2 Lower jaw had many bones 3 QuadrateArticular jaw articulation 4 There was no tympanumtypmanic bone angular was in the lower jaw 5 There was a very large stapes This connected the inner ear to the jaw via the quadrate Vibrations at the jaw joint were transmitted to the inner ear by the stapes Inference is that this is how pelycosaurs detected low frequency sounds They rested their lower jaw on the ground to detect vibrations So the chain of transmission would have been Dentary gt Articular gt Jaw Joint gt Quadrate gt Stapes gt Inner Ear This is the condition seen in many modern snakes The Quadrate amp Articular functioned both as the jaw articulation and in sound transmission There s a interesting diagram of this at the following web site httpwwwpalae0scomVertebratesUnitsUnit420420300html This diagram can be useful in understanding how the QA jaw functions but can be very confusing on first glance You won t be required to reproduce this diagram use it at your own discretion The structure of the QA jaw sets the stage for subsequent evolution Jaw Musculature Jaw Adductors were simple Temporalis is the only muscle we ve seen evidence for Temporalis formed essentially a straight line from CF to the braincase Coronoid Process was rather low Key Point The force of the temporalis was directly vertical and right over the Coronoid Because the upward force of the temporalis and the downward force of the bite resistance are offset there is a lever action This then generates forces in both directions at the jaw joint S0 in early synapsids a powerful bite resulted in strong forces acting right at the jaw joint As a result the joint needs to be strongly braced and the quadrate and articular were constrained to be very robust bones V Cynodonts Late Therapsids A First major change in jaw adductors They become larger and more complex and this is associated with cynodonts higher activity This is where we see the rst evidence of a masseter This new muscle actually splits off from the temporalis We see this embryonically in modern mammals B Of course as we ve discussed we also see a huge and gradual increase in the size ofthe temporal fenestra as well as an expansion of the braincase C In addition we see a concurrent expansion of the coronoid process Temporalis up and back Masseter up and forward Now if we analyze force vectors The line of action of the temporalis intersects the line of action of the masseter well out over the jaw actually right over the bite point So we can resolve the vectors around the bite point All forces cancel out no stress at the jaw joint Because of the height of the coronoid process and the evolution of the masseter Cynodonts could produce much bite force without imposing any stresses at all at the lower jaw So now the quadrate and articular are free of the constraint of having to be large and robust in order to withstand the stress of feeding They can now respond to selection for increasing ef ciency of transmission of sound vibrations They still form the jaw joint but now are free to become small This is illustrated remarkably clearly in the fossil record As the coronoid process expands the quadrate and articular become gradually smaller See httpwww 39039 mb f 1 39 I html D At the same time we see the rst evidence of an eardrum or tympanum supported by the lower jaw speci cally by the laminar process of the angular At this point then there is a new chain of transmission Cynodont chain of transmission Tympanum gt Angular gt Articular gt H gt Quadrate gt Stapes gt Inner ear Again the bones involved in transmission of sound vibrations would have been under selection to become small because smaller objects transmit vibrations more efficiently The quadrate and articular are still functioning as the jaw joint but have responded to selection to become smaller As these get smaller the dentary in the lower jaw and the squamosal bone in the cranium expand to ll the space Eventually the dentary and squamosal come into contact We saw this in P 39 39 and Dim Again check out the site httpwwwpalaeoscomVe1tebratesUnitsUnit420420300html Once this happens the quadrate and articular are no longer constrained to form the jaw joint We see a second release from constraints Articular migrates off the lower jaw gt Malleus Quadrate migrates off the upper jaw gt Incus The angular is then lost off the lower jaw and fuses to the braincase gt tympanic which encases the others in the middle ear cavity So there still is an articulation that is homologous to the ancestral jaw joint If we look at the developing Didelphis embryo we see the malleus first ossifies on the lower jaw and the incus ossifies on the cranium and actually articulates with the malleus there In addition the tympanic bone ossifies on the lower jaw right where the angular is in fossil cynodonts At the point in development when the braincase expands these three elements move away from the lower jaw and fuse to the cranium New chain of transmission Tympanum gt Malleus gt Incus gt Stapes gt Inner ear Mammalogy Lecture 6 Dentition 1 Let s move on to the topic of dentition You ll be learning a lot of terms here but we ll really only scratch the surface of the study of mammalian dentition II In general A Anatomy 7 There are two materials that form the hard parts dentine and enamel Enamel covers the crown of the tooth in only a few species of mammals such as humans Dentine is softer than the enamel and wears away faster The enamel then forms ridges and cusps and much of the pattern of the occlusional surface is formed by wear Root is open while tooth is growing and there is a blood supply to fuel this growth When tooth is fully developed the root may close off such that blood supply is cut off Brachydont ancestral In some forms herbivores the root never closes off and the tooth is evergrowing Hypsodont high crowned These teeth then require constant wear or animal will die B Differentiation Looking up at the palate of a human incisors croppers and nippers premaXilla canines puncture and hold premolars slice and grind molars slice and grind Eutherians only molars are nondeciduous that is single generation Metatherians only the last premolar is deciduous III Dental formulae There is a great deal of variation in which teeth are present across the mammal groups and mammalogists have a shorthand way of expressing the complement of teeth that characterizes a particular species This is called the dental formula Exemplify this by Homo sapiens 22 i ll c 22 p 33 m 32 orjust 22 ll 22 33 32 Note that this just refers to one half the jaw either the right or left side Primitive metatherian dental formula is 54 11 33 44 50 A unique aspect of marsupials is that they always have more upper incisors than lower Primitive eutherian dental formula is 33 11 44 33 44 In only a few groups have additional teeth evolved Odontocetes toothed whales have gt100 There are many groups that have fewer teeth than this and the phylogenetic tendency is to lose teeth Teeth are lost in a particular pattern over the course of evolution not ontogeny incisors posterior are lost first premolars anterior premolars are lost first molars posterior are lost first So if a group has only two premolars it s the lSt and 2quotd that have been lost and the 3rd and 43911 that are retained IV Different types of Cheek Teeth Dietary habits lead to the adaptations of different types of teeth DRAWINGS Metatherian and Eutherian Triboshpenic Molars Dilambdodont 7 Insectivorous diet SecodontCarnassial 7 Carnivorous diet Bunodont 7 Omnivorous diet Selenodont 7 Herbivorous diet Lophodont 7 Herbivorous diet Mammalogy Lecture 10 Locomotion III Types of Locomotion I In general we can recognize several types of locomotory specializations in mammals In addition to powered ight we see a Saltatorial Hopping b Cursorial Running c Scansorial Climbing d Gliding e Swimming Most groups are pretty generalized but there are many specialists that do one of these particularly well 11 Saltatorial Bipedal hopping usually is seen in prey species and is also known as ricochetal locomotion This is seen in several groups Macropodids Paremelids some primates such as these ringtail lemurs In fact has evolved at least ve different times independently just in rodents Heteromyidae Kangaroo rats and mice Pedetidae Springhares South African family of rodents Dipodidae Old World forms such as jerboas and the local jumping mouse Zapus Mirunae Old World mice that are saltatorial Gerbillinae Gerbils A All these forms have very long hind limbs They all have responded to selection to optimize V0 amp they have very long out levers on their hind limbs B To compensate for the tradeoff that this implies with power they also have really large hind limb musculature in fact it s hard to imagine more lopsided beast than a Krat There often is a reduction in number of digits in the hind limb The forelimb is almost always very generalized and is used in feeding grooming etc C Other adaptations l Stiffening of the spine to resist whiplash cervical vertebrae are often fused in saltators lumbar vertebrae tend to be robust the sacrum and pelvic girdle are strongly fused There are ligaments running from thoracic to cervical vertebrae and from sacral to lumbar vertebrae these function in shock absorption 2 Use elastic storage mechanisms to save energy hind limb ligaments are elastic At moderate constant speeds saltation is more efficient than running 3 Long counterbalancing tail that may used to change direction in mid air is often tufted to add weight D Advantages 7 Saltation enables extremely rapid acceleration It is also very amenable to sudden changes in direction Krats can actually change direction in midair predator avoidance II Cursorial Adaptations for running are seen in both predators and prey For example Lagomorphs terrestrial Cetartiodactyls gira ids cervids bovids antilocaprids Perissodactyls Camivora canids and felids Thylacynids all are cursorial In general there are two ways that cursorial mammals increase speed Increased Stride Rate amp Increased Stride Length A Increase stride length 1 Typically the distal limb bones are elongated this increases stride length 2 Change in foot posture Plantigrade Generalized noncursorial condition palm on the ground Digitagrade 7 Canids Felids Leporids only digits on ground metapodials are lengthened Unguligrade Terrestrail Cetartiodactyls and Perissodactyls Only the hoof on the ground Hoof is a modified claw or ungula This then allows for the extreme expansion of metapodials fusion into cannon bone 3 Loss Reduction of clavicle allows the scapula to pivot and rotate as part of the limb as well because it does not articulate with the axial skeleton Front limb is supported by a muscular sling formed by the trapezius rhomboideus serratus and pectoralis This also acts to absorb the shock of the limb striking the ground 4 Increased dorsoventral exion of the spine Extreme in cheetahs the fastest mammals have a bounding leaping run up to 110 Kmhr 70 mph This has a huge energetic cost because the entire body has to be lifted with each stride This works well for rapid bursts but not for cursors that are endurance runners or for large cursors with high body weight So horses only exhibit moderate dorsoventral flexion B Increase stride rate This is tied to optimizing V0 1 Short inlevers and long out levers olecranon process for front limb calcaneum for hind limb Thus lengthening the distal portion of the limb has a dual advantage for cursors 2 Increase the number of joints V0 Total Sum of all V0 in limb scapula rotating inclusion of wristankle associated with digitagradeunguligrade VoTotal VoScapula V0Humerus VoUlna VoCannon Bone VoHoof 3 Decrease inertia of limb distally decrease the distal mass of the limb so less E is required to move it quickly loss of peripheral digits reduce to splints Terrestrial Cetartiodactyls only the 3rd and 4th are well developed Perissodactyls third digit is well developed others vestigial Confining movement to a single plane Ungulates Astragalus acts as a tongue and groove system between forelimb and expanded metapodials Concentration of muscles to the proximal locations long tendons very slender limbs III Scansorial Climbing A There are many climbing mammals of all kinds Climbing creates a need to move in a complex 3 dimensional environment It s pretty obvious that there would be great adaptive significance of traits that reduce the likelihood of falling However the danger of falling is more sever for large bodied climbers than small because small ones have a much lower terminal velocity maximum velocity that can be reached This relates to surface area to volume ratio Large climbers therefore tend to be slow and cautious small ones more acrobatic B Usually there is some type of modi cation to increase friction between feet and substrate 1 Friction pads on hands feet and digits Primates Porcupine Erethz39zon dorsatum Raccoon 7 Procyon lotor 2 Claws for digging into the substrate Most scansorial rodents especially well developed in squirrels Sciurus 3 Prehensile organs tail Opossum Cyclopes Silky anteater Coendu Prehensile tailed porcupine Primate family Cebidae new world monkeys opposable digits 7 opossum primates and Phascolarctos 4 Suction cups suckerfooted bats in the family Myzopodidae C Typically have stiffened trunks to resist bending l Vertebral column robust 2 Expanded ribs that overlap 3 Elongated thoracic region 4 Lumbar shortening decreases movement between pelvis and ribs D Typically have elongated forelimbs opposite to saltators One very specialized mode of scansorial locomotion is brachiation Gibbons IV Gliding A Gliding has evolved several times seemingly always from an arboreal form A number of marsupials Petauridae Rodents At least twice Anomalurids and Sciurids Dermoptera Cynocephalidae B In all cases the ight membrane involves a webbing of skin between the front limb and hind limb In dermopterans the ight membrane also encompasses the tail and comes up to the lower jaw This ight membrane is often extended somewhat by stylar cartilage that extends into the wing The thinking had always been that these functioned to increase the surface are of the patagium but that s not really accurate Any object moving through a viscous medium including air experiences drag Drag is caused by air vortices that can impede movement through the air in several ways One that we ll worry about is called induced drag air vortices spilling from the wing tips resulting in downward pressure These cartilages aren t directed straight out during ight they re actually directed upwards This has the effect of displacing the induced drag so it s no longer placing downward pressure C Thus these combine to affect a controlled fall amp animals can get from tree to tree without descending There are fewer predators in the trees D Glaucomys can glide up to 50 meters or more When they land they have a very intersting habit of always scooting around to the opposite side to the trunk interpreted as predator avoidance following owls E One particularly cool gliding mammal is Eupetaurus the wooly ying squirrel This occurs in Pakistan and China and lives in caves above tree line At night they glide down to the forests to feed on pine needles and climb back up during the night V Swimming Every of mammal can swim Let s just consider those modi ed for swimming Drag is much more of an issue for swimmers than for gliders because water is more viscous than air A Pressure Drag Drag caused by having to displace the water through which the animal is moving Proportional to crosssectional area so a rod shape shape is very long and thin minimizes pressure drag B Frictional Drag 7 Drag associated with laminar ow created by the friction between parallel streams of water Proportional to the surface area so a sphere is the shape that minimizes surface area So we see again a direct trade off It turns out that the shape that results in the lowest overall drag is a spindle which optimizes the tradeoff Therefore we tend to see fusiform bodies C Adaptations to swimming 1 Semiaquatic forms shrews Sorexpalusm39s mustelids Lutrines otters Lutra canadensis Rodents beaver capybara nutria muskrats Cetartiodactyla Hippopotamus Usually these animals have long bodies and swim primarily with limbs Almost always some type of modi cation of webbing to increase thrust Exception is the family Hippopotamidae actually take the opposite route and actually walk along the oor of the river 2 Fully aquatic Cetaceans Pinniped carnivorans amp Sirenians a Limb modi cation 1 front limbs modi ed into ippers entirely syndactylous may provide thrust Otariids Sea lions and fur seals may be used as rudders 7 Phocids Earless seals Cetaceans Odobenids Walrus 2 Hind limbs may be vestigial as in cetaceans and sirenians fossil cetaceans with actual hind limbs may be modi ed into ippers for propulsion as in seals Phocids these forms actually can t use their hind limbs for terrestrial locomotion Otariids actually can b Axial Skeleton modi cation Especially seen in cetaceans 1 Reduction of cervical vertebrae essentially no neck Water is a viscous medium All cervical vertebrae are present but they re compressed and fused 2 Fusion of atlas and aXis 3 Increase in robustness relative to terrestrial vertebrates to resist compression associated with the viscous medium c Flukes Tail ns of mammals both cetaceans and sirenians as well as dorsal ns have no skeletal component They are entirely brous connective tissue D The secondary evolution of aquatic lifelstyle in whales is well documented by fossil intermediates This was rapid probably occurring over ca 8 MY but there are several transitional fossils Pakicetus fossils are from ca 52 MYA and had functional hind limbs Ambulocetus fossils are from 49 MYA and also had functional hind limbs Basilosaurus is known from 40 MYA and has fully formed but extremely small hind limbs It was fully aquatic and very large This research including a discussion of the scienti c controversies is available on Hans Thewissen s web site httpdarlaneoucomeduDEPTSANATThewissen Mammalogy Lecture 5 Disparity in Diversity between Marsupials and Placentals So as we ve seen over the last couple weeks Eutheria is much more diverse than Metatheria This is true in terms of the numbers of species there are over 4350 eutherian species and ca 270 metatherian species It s also true with regard to diversity in form For example there are no fully aquatic marsupials and there are no marsupials with powered ight So today we ll discuss two hypotheses regarding the primary reason for this and both have to do with reproduction A Trophoblast Hypothesis The principle difference is the trophoblast part of the embryonic contribution to the placenta that is welldeveloped in eutherians but not metatherians Embryoblast amp Trophoblast Trophoblast implants into the uterine wall it develops fingerlike projections into the uterine wall It has many functions but we ll worry about one Now all mammals reproduce sexually and so there is a genetic contribution of the father Because of this the developing embryo will be recognized as foreign tissue by the immune system of the mother and potentially trigger an immune response The trophoblast actually provides a barrier that separates the embryonic tissues from the immune system of the mother yet still allows for the passage of nutrients In many eutherians this is known to be accomplished by production of chorionic gonadotropins which among other things maintain the trophoblast and suppress maternal immune reaction Therefore the developing eutherian embryo can hide from the mothers immune system and this allows for a relatively long period of intrauterine development in eutherians These long gestation times then result in more fully developed precocial young In metatherians there appears to be little or no suppression of the maternal immune response There is no ba1rier between the developing embryo mother s immune system Metatherians therefore lack the ability for the embryo to hide Thus to avoid attack from the mother s immune system metatherians have a very short gestation For example M acropus typically has a gestation period of around 30 days and Didelphis has a gestation period of around 12 days Metatherians give birth to very poorly developed young altricial Neonates attach to nipples and complete development This has two effects 1 Metatherians have a much longer overall period from conception to weaning 2 In metatherians a higher percentage of time is spent lactating Lactation is about twice as energetically costly as gestation Therefore eutherians experience a lower overall energy cost of reproduction and have a competitive advantage over metatherians Figure 915 in text illustrates the difference in investment in reproduction This competitive advantage explains the difference in species diversity between metatherians and eutherians Also this longer gestation in eutherians allows for increased diversity in morphology especially with regard to the forelimb When metatherians are first born because of such short gestation times they are remarkably poorly developed Hind limbs are simply limb buds amp organogenesis has only just begun In spite of this they actually have to crawl from the birth canal to the mammae which may or may not be inside a pouch where they attach and complete development Almost no assistance in offered by the mother The most she may do is lay a saliva trail from birth canal to marsupium Because of this the forelimbs of all marsupials are rather constrained That is not free to evolve into such things as the wings of bats or the ippers of marine mammals Summary the presence of a welldeveloped trophoblast in eutherians and the production of chorionic gonadotropins allows the embryo to hide from mother s immune system and thereby allows greater gestation time This reduces overall cost of reproduction relative to metatherians and allows for greater diversity in morphology especially of the forelimb Therefore the trophoblast hypothesis explains both the disparity in species numbers and also the disparity in morphological diversity B Basal Metabolic Rate Hypothesis The fundamental difference is not the trophoblast but differences in the relationships of the following Diet Basal Metabolic Rate Reproductive Capacity In Eutherians BMR is directly coupled to Reproductive Capacity increase BMR increase Reproductive Capacity Metatherians lack this direct coupling for whatever reason increase BMR no change in Reproductive Capacity So under this hypothesis then in situations in which eutherians can evolve high BMR expect that they will outcompete metatherians because eutherians can translate high BMR to higher reproductive rates Conversely where a high BMR can t be supported there should be no competitive difference between eutherians and metatherians amp they should be able to coexist This is where diet becomes relevant High BMR incurs high energetic cost Therefore it can evolve only where food is either very high quality or very abundant We expect that eutherians grazers and carnivores will outcompete metatherian grazers and carnivores High BMR cannot evolve in situations in which food is either low in abundance and or quality This is the case for frugivores and opportunistic feeders We expect there to be no competitive advantage for eutherians These ideas seem to be supported by fossil records and distributions Marsupials radiated in both Australia and South America in relative isolation from placental mammals In South America there is fossil evidence that there were marsupial carnivores but when North and South America came back into contact 3 MYA eutherians invaded South America marsupial carnivores went extinct and frugivores and opportunistic feeders persist The majority of marsupial diversity is in Australia where there were no eutherian competitors In fact we see both carnivorous and grazing marsupials only here Furthermore introduction of the dingo into Australia resulted in the extinction of the Thylacine or marsupial wolf and the restriction of the Tasmanian deVil Sarcophilus to Tasmania There was an argument in the literature over which of these was the principle reason for the disparity in diversity that we see between marsupials and placentals Both these ideas have merit and are probably contribute to some degree to the patterns of diversity that we see today If I were forced to choose one of these hypotheses I would choose the Trophoblast Hypothesis because it has greater explanatory power It explains both the difference in species numbers and the difference in morphological diversity The BMR hypothesis only explains species numbers