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Popular in Evolutionary Biology: Diversity of Life
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This 18 page Class Notes was uploaded by Samantha R on Sunday October 11, 2015. The Class Notes belongs to EBIO 1040-01 at Tulane University taught by Michael Doosey in Fall 2015. Since its upload, it has received 52 views. For similar materials see Evolutionary Biology: Diversity of Life in Biology at Tulane University.
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Date Created: 10/11/15
Arthropoda Ch34 Friday ctober 9 2015 1203 PM 0 Learning Objectives 0 Learn the taxonomy of subphyla classes amp some orders 0 Understand hexapodainsecta life history amp metamorphosis SUBPHYLUM MARYAPODIA Chilopoda amp Diplopoda 0 Class Chilopoda Centipedes 0 3000 Species O Terrestrial 0 Body Plan I Flattened bodies I Up to 177 segments I 1 Pair of legs per segment I Appendages of lst body segment form poison claws Carnivorous I Eat earthworms cockroaches amp other insects Mostly harmless to humans I Some tropical centipedes are dangerous 0 Class Diplopoda Millipedes O 10000 Species 0 Body Plan I Cylindrical bodies I 25100 segments I 2 Pairs of legs per segment 0 Most eat decayed plants I Few eat living plant tissue 0 Some secrete toxicrepellant fluids SUBPHYLUM CRUSTACEA 0 Diversity 0 67000 living species 0 Marine some freshwater I quotInsects of the Seaquot 0 Crabs Shrimp Lobsters Barnacles Crayfish Copepods Pill bugs amp Sand fleas 0 Body Plan 0 3 Tagmata I Head amp Thorax fused to form a cephalothorax I Abdomen 0 Head I 2 pairs of antennae 1 pair are antennules I 3 pairs of appendages for chewing I Anterior end head may have a nonsegmented rostrum El 1 Pair of mandibles El 2 Pairs of maxillae O Appendages are biramous 2branched I 1 Pair of appendages per segment 0 Last abdominal somitetagma consisting of Telson amp Uropods forms a tail 0 O Oct 9th Page 1 O Carapace Dorsal covering hard upper shell I Covers most of body or just cephalothorax 0 Gas exchange through gills or across cuticle 0 Most have a larva unlike the adult in form amp undergo metamorphosis O Nauplius Common larval form I Evidence of common ancestor for diverse group 0 Class Malacostraca 0 Diversity I 20000 Species I 3 Subclasses amp 14 Orders 0 Order Isopoda I Only truly terrestrial crustaceans I Also have marine amp freshwater forms I Common landforms include sow bugs amp pill bugs I Some are highly modified as parasites as fish I Body Plan I Dorsoventrally flat I Lack a carapace I Have sessile compound eyes 0 Order Amphipoda I Resemble isopods I Compressed laterally I Gills are in thoracic region I Many are marine El Others are beachdwelling freshwater or parasitic 0 Order Decapoda I 18000 Species I Crayfish lobsters crabs amp true shrimp I Appendages El Five pairs of walking legs 9 It crabs the first pair of walking legs form pinchers El 3 Pairs of maxillipeds El Legspan ranges from a few millimeters to 35 meters I Cephalothorax covered by carapace that SUBPHYLUM HEXAPODA 0 Class Insecta 0 Diversity I Largest group of animals I More the half the animal species I One billion billions 1018 insects are alive right now I Found in nearly all habitats except the sea I Common in freshwater brackish water amp salt marshes El Abundant in soils forest canopies deserts amp wastelands 0 Adaptive Traits I Flight amp small size make insects widely distributed I Wellprotected eggs withstand rigorous conditions amp are readily dispersed 0 Body Plan I 3 Body Regions Oct 9th Page 2 El Head El Thorax 9 Has 3 segments each with a pair of legs 9 Many have 12 pairs of wings outgrowths of body wall I Abdomen I Universal mouthpart structures III Modifications reflect eating habits 0 Internal Organization I Tube digestive tract III Digestion takes place in stomach midgut I Excretion takes place through Malpighian Tubules III Malpighian Tubules Extensions of the hindgut that save water amp excretes solid waste I Winged insects have dilated tracheae forming air sacs III Formed bellows to force air deep into body III Spiracles through which air enters the tracheal system 0 Sensory Receptors I Sensory setae III Detect chemical amp mechanical signals I Tympanum A thin membrane associated with tracheal air sacs El Detects sound I Pheromones used to communicate III Pheromones A chemical excreted by an animal affecting the behavior or physiology of others of its species III Mating signals trail markers 0 Many insects undergo metamorphosis I Metamorphosis Radical change in morphology during development via series of molts I Hemimetabolous Metamorphosis where immature stages nymphs are similar to adults III Simple metamorphosis I Holometabolous Metamorphosis including a larval wormlike form which is then proceeded by a pupalresting stage and then finally molts into an adult form III Complete Metamorphosis O Insects amp Human Welfare I Beneficial Insects III Insects produce honey beeswax silk amp shellac III Bees pollinate 10 billion worth of food crops in the US annually III They39re critical components of most food chains amp an important food source for many fish amp birds I Harmful Insects III Some eat amp destroy plants amp fruits III Nearly every cultivated crop has several insect pests III Some destroy food clothing amp property I Medically important insects include vectors for disease agents III Malaria is carried by Anapheles mosquitos III Fleas carry plaque a disease that changed human history in the Middle Ages Oct 9th Page 3 El West Nile virus is carried by mosquitos TAXONOMY 0 PhylumArthropoda O SubphylumTrilobita O SubphylumChelicerata I Class Merostomata I CIassArachnida El OrderAraneae El OrderScorpiones El OrderAcari O Subphylum Myriapoda I Class Chilopoda I Class Diplopoda O SubphylumCrustacea I Class Malacostraca I Order Isopoda El OrderAmphipoda I Order Decapoda O Subphylum Hexapoda I Classlnsecta Oct 9th Page 4 Echinoderms and Protochordates Ch35 Monday October 12 2015 1000 AM 0 Learning Objectives 0 Understand differences between protostomes and deuterostomes 0 Know Echinoderm morphology and taxonomy 0 Know the four characteristics of Chordates 0 Learn the subphyla of Chordata 0 KingdomAnimalia O Subphylum Eumetazoa I Clade Bilateria El Protostomia El Deutrostomia 9 Phylum Echinodermata 9 Phylum Chordata Review Differences Between Deutrostomes amp Protostomes O Protostomes first mouth develop the mouth first from or near the blastopore O Deuterostomes second mouth develop the anus first from the blastopore 0 Evolution of the Animal Body Plan 0 Deuterostomes differ from protostomes I Cleavage pattern of embryonic cells I Protostomes Spiral cleavage El Deuterostomes Radial cleavage I Developmental fate of cells I Protostomes Determinate development I Deuterostomes Indeterminate development PHYLUM ECHINODERMATA 0 Diversity 0 6000 Species I Sea stars brittle stars sea urchins sand dollars sea cucumbers 0 Greek spine derma skin 0 Marine NO EXCEPTIONS 0 Origin remains unclear I Thought to have evolved from bilaterally symmetrical ancestors because larvae are bilaterally symmetrical 0 Symmetry O Pentaradial as adults I 5 axes of symmetry 0 All systems organized with branches radiating from the center 0 Nervous system consists of a nerve ring with branches I No centralization of function 0 Endoskeleton O Composed of calcium carbonate plates just beneath the skin 0 May be tightly or loosely joined 0 All members have mutable collagenous tissue Oct 12th Page 1 0 Open Circulatory System 0 Large coelom functions both in respiratory amp circulation 0 WaterVascular System 0 Aids in movement amp feeding O Radially organized 0 Process 1 Water enters through madreporite 2 Water flows through stone canal gtring canal 3 Radial canal extends from the ring canal into each body branch 0 Tube Feet may have suckers I Tube feet are generally on the oral side to make contact with substrate I Locomotion an feeding by means of tube feet 0 Reproduction 0 Regeneration I Many able to regenerate lost parts I Some reproduce asexually by splitting 0 Most reproduction is sexual I Separate sexes I Gametes release into water I Freeswimming larvae El Each class has a characteristic type of larvae 5 CLASSES not extinct of Echinodermata 0 Class Asteroidea sea stars amp sea daisies 0 Important predators in many marine systems 0 Most have 5 arms I Some have 6 or multiples of 5 0 Class Echinoidea sea urchins amp sand dollars get pic of bothmake sure it39s a live sand dollar 0 Lack arms 0 Double rows of tube feet 0 Protective moveable spines 0 Some eat the uni eggs of a sea urchin 0 Class Ophiurodea brittle stars 0 Largest class 0 Probably most abundant group in terms of s of species amp s of individuals in a habitat O Arms are equal diameter their entire length unlike starfish that go like this gt 0 Very brittle O Often hunted by large starfish 0 Class Crinoidea sea lilies amp feather stars 0 Class Holothuroidea sea cucumbers O Superficial 5 radial symmetry O Skeletal plates under the skin reduced NEXT PAGE FOR INTRO TO CHORDATA gt Oct 12th Page 2 Chordata Ch35 Wednesday October 14 2 15 1 2 AM Introduction on Oct 12th PHYLUM CHORDATA Chordates are deuterostome coelomates Nearest relatives are echinoderms only other deuterostomes Fishes amphibians reptiles birds amp mammals Distinguishing Features Fig 354 0 Nerve Chord O Notochord I Provides a stiff primitive endoskeleton so that the organism can move I Beneath the nerve chord O PharyngealSlitsPouches I Originally evolved for filter feeding in water I Later was adapted for respiration O PostAnal Tail I In other organisms the anus is the most posterior thing on the body Other Distinguishing Characteristics 0 Chordata muscles are arranged in segmented blocks somites 0 Most chordates have an internal skeleton against which the muscles work what does this mean Chordate Characters in Adults in regards to humans 0 Nerve Chord gtSpinal Chord amp Brain 0 Notochord gtReplaced by bony vertebrate vertebral column 0 Pharyngeal SlitsPouches gtMost are lost except for one that becomes the Eustachian Tube I Some remnants help form thyroid gland and other things 0 PostAnal Tail gtRegresses coccyx bone I Sometimes infants are born with a slight remnant but it is removed in surgery I This clearly does remain in other species 3 SUBPHYLUMS Subphylum Urochordata 0 1300 Species Greek Ouratail Latin Chordacordtunicates Sessile marine organisms as adults Covered with cellulose cloak or tunic Tunicates amp Salps are marine animals I Get image of tunicate I Larval amp Adult Stages El Larvae 9 Tadpolelike have notochord amp nerve chord 9 Freeswimming but don39t feed 9 Get diagram of larvae 357 9 Has all characteristics of chordates they will further develop as they grow 0000 Oct 14th Page 1 El Adults 9 Typically lose tail amp notochord 9 Immobile filterfeeders 9 Many secrete a tunic cellulose sac that surrounds the animal I Use pharyngeal slits to exchange gases amp feed I Pharynx lined with cilia El Draws water in through incurrent siphon amp out through excurrent siphon El Suspended organic particles stick to layer of mucus in the pharynx I Get image amp diagram of tunicate fig 357 amp diagram 0 Subphylum Cephalochordata O 0000 0000000 Greek Khephale head Latine chordachord 30 Species lancelets Amphioxus what do those words mean Closest relatives to vertebrates Common in shallow marine waters Hard to see because they39re buried in the sand with only their mouth sticking out I Spend most of their time partially buried Notochord persists throughout lifetime Feed on plankton using ciliagenerated currents Get diagram amp image fig 356 Filter feed by means of pharyngeal slits Sedentary Cephalization greatly reduced Segmented musculature mesoderm I Independently evolution of segmentation not inherited from protostomes I Segmentation in chordates is probably an adaptation of burrowing as in annelid worms Oct 14th Page 2 Cho rdata Ch35 M wryi1 A 3er 7 w gm 3 5 E 47 a gt a F 1 7 l Lela L L Introduction on Oct 12th PHYLUM CHORDATA 0 Chordates are deuterostome coelomates I Nearest relatives are echinoderms only other deuterostomes Fishes amphibians reptiles birds amp mammals Distinguishing Features Fig 354 O O I Provides a stiff primitive endoskeleton so that the organism can move I Beneath the nerve chord O I Originally evolved for filter feeding in water I Later was adapted for respiration O I In other organisms the anus is the most posterior thing on the body I Chordate Characters in Adults in regards to humans 0 Nerve Chord gtSpinal Chord amp Brain 0 Notochord gtReplaced by bony vertebrate vertebral column 0 Pharyngeal SlitsPouches gtMost are lost except for one that becomes the Eustachian Tube I Some remnants help form thyroid gland and otherthings PostAnal Tail gtRegresses coccyx bone I Sometimes infants are born with a slight remnant but it is removed in surgery I This clearly does remain in other species 0 Other Distinguishing Characteristics 0 Chordata 0 against which the muscles work what does this mean 3 SUBPHYLUMS I Subphylum Urochordata 0 1300 Species 0 Greek Ouratail Latin Chordacordtunicates O O 0 Covered with cellulose cloak or tunic o I Get image of tunicate I Larval amp Adult Stages III Larvae 0 Tadpolelike have notochord amp nerve chord 0 Get diagram of larvae 357 0 Has all characteristics of chordates they will further develop as they grow III Adults 0 Typically Oct 14th Page 1 lthamwmmdsmeamma39 I I Pharynx lined with cilia D I Get image amp diagram of tunicate fig 357 amp diagram I Subphylum Cephalochordata 0 Greek Khephale head Latine chordachord O 30 Species Iancelets Amphioxus what do those words mean 0 Closest relatives to vertebrates 0 Common in 0 Hard to see because they39re buried in the sand with only their mouth sticking out throughout lifetime Get diagram amp image fig 356 OOOOOOO not inherited from protostomes I Segmentation in chordates is probably an adaptation of burrowing as in annelid worms NOTES FOR TODAY SUBPHYLUM VERTEBRATA Learning Goals 0 Distinguish Vertebrates from other Chordates 0 Learn the classes of Subphylum Vertebrata 0 Know how jaws evolved in fishes 0 Understand the adaptations for the invasion of terrestrial habitats by vertebrates TAXONOMY 0 Kingdom Animalia O Subkingdom Eumetazoa I Deuterostomia III Phylum Echinodermata III Phylum Chordata 0 Subphylum Urochordata 0 Subphylum Cephalochordata 0 Subphylum Vertebrata SUBPHYLUM VERTEBRATA I Vertebrates are chordates with a spinal column Distinguished from nonvertebrates by O Vertebral Column I Encloses amp protects the dorsal nerve chard 0 Head I Distinct amp welldifferentiated possessing sensory organs Oct 14th Page 2 0 Other Characteristics 0 Neural Crest I Unique group of embryonic cells 0 Internal Organs I Liver Kidneys Endocrine glands heart amp closed circulatory system 0 Endoskeleton I Made of cartilage or bone I Makes large size amp movement possible 0 Brief History of Vertebrates O lst appeared in the oceans about 545 million years ago I Mouth on end fin the other 0 Jawed fishes soon became dominant O Amphibians invaded the land 0 Reptiles replaced them as the dominant land vertebrates 0 Birds amp mammals became dominant after Cretaceous mass extinction FIS 0 Most diverse group O 30000 Species 500 families 0 Over half of all vertebrates 0 Provided the evolutionary base for invasion of land by amphibians 0 Characteristics 0 Vertebral Column I Hagfish amp lamprey exceptions Jaws amp paired appendages I Hagfish amp lamprey exceptions Internal Gills Singleloop Blood Circulation Nutritional Deficiencies I Inability has been inherited by all their vertebrate descendants 0 Evolution ofJaws 1 The lst fishes had mouths with no jaws I Hagfish Class Myxini amp Lampreys Class Cephalaspidomorphi 2 Development ofjaws occurred in the late Silurian period I Evolved from the anterior gill arches that were made of cartilage 3 Pharyngeal Gills Slits I Gills slits appear in the pharynx of all chordates at some point I Gills slits in pharynx evolved to aid in respiration amp filter feeding I Larger more active chordates need more oxygen gttissue between slits become highly folded more surface area Gill arches become reinforced with cartilage to hold slits open Gill arches become ossified bony Boney gill arches migrate forward Arched form primitive bitingjaw I Vertebrates no longer limited to filter feeding O Devonian Period I Known as quotage of fishesquot O O OO NP SquotP Oct 14th Page 3 I Armored fishes placoderms amp spiny fishes acanthodians both had jaws El Acanthodians common during early Devonian 9 Cartilages skeleton but skin had small plates of bond El Placoderms common in late Devonian 9 Much improved jaw I the end of Devonian period essentially all of these pioneer vertebrates disappeared I Replaced by sharks amp bony fishes in one of several mass extinctions 400 million years ago I Jaw was improved even further allowing the mouth to open much wider than was previously possible 0 CLASS CHONDRICHTHYES sharks skates rays 0 O 0 750 Species Became the dominant sea predators in the Carboniferous period 280 Million years ago Cartilage Skeleton I Calcified with granules of calcium carbonate I Light strong skeleton Sharks were among the lst vertebrates to develop teeth I Evolved from rough scales on mouth39s skin I Easily lost but continuously replaced Sharks amp bony fishes have fully developed lateral line system I Series of sensory organs under the skin that detects changes in pressure waves Reproduction I Different from other fishes I Eggs fertilized internally I In most species the young grow inside the mother amp are born via live birth vivaparous Sharks have long gestation periods amp few offspring I Not able to recover quickly from population declines Boney Fishes I Evolved the same time as sharks about 400 million years ago I Adopted a heavy internal skeleton completely of bone I Most speciesrich group of all vertebrates 30000 species I Significant adaptations include swim bladder amp gill cover Swim Bladder El GasFilled Sac that allows bony fishes to regulate buoyancy El Filled amp drained with gases internally Gill Cover El Hard Plate Operculum covers gills El Flexing plate permits water pumping over gills El Efficient bellows system when stationary 0 Class Actinopterygii Rayfinned fishes O 0000 Parallel bony rays support stiffen each fin There are no muscles within the fins Most diverse vertebrate class 50 Orders Aquatic SPECIES Oct 14th Page 4 O Paedocypris smallest vertebrate 10 mm long 0 Beluga Sturgeon 7 meters long 0 Class Sarcoptergii Lobefinned Fishes Have paired fins that consist of a long fleshy muscular lobe Supported by central core of bones with articulated joints Almost certain that they39re amphibian ancestors SPECIES Coelacanth I Thought to be extinct since Mesozoic Era O O O O Rediscovered in 1938 off Southern Africa Lungfish I Tropical freshwaters I Some species can live out of water for long periods of time Burrow deep in mud before lake dries amp estivate until wet season 0 Class Amphibia 0 Diversity 3 clades 5670 Species El 37 Families 0 First vertebrates to walk on land 0 Direct descendants of fishes O 5 Distinguishing Features Legs Lungs Cutaneous Respiration El Supplement lungs Pulmonary Veins El Separate pulmonary circuit allows higher pressure blood to tissues Partially Divided Heart I Improves separation of pulmonary amp systemic circuits 0 Successful invasion of land by vertebrates required several adaptations Legs gtsupport body39s weight Lungs gtExtract oxyegn from air Redesigned still in water to prevent egg drying System to prevent whole body desiccation O Ichthyostega Evolved from lobefinned fish One of the first amphibians Sturdy forelegs flippershaped hind limbs El Moved like a seal Long broad overlapping ribs forms solid cage for lungs amp heart 0 Tiktaalik Oct 14th Page 5 I In 2006 a transitional fossils was found between fish amp Ichthyostega I Had gills amp scales like a fish but a neck like an amphibian I Shoulder forearm amp wrist bones were like those amphibians but the end of the limb was a lobed fin ORDERS 0 Order Caudata Salamanders I Long bodies amp tails I Smooth moist skin I Live in moist places I Eggs Internally fertilized I Larvae similar to adults 0 OrderApodaCaecilians I Tropical burrowing amphibians I Legless with small eyes amp jaws with teeth I Fertilization is internal Oct 14th Page 6 Chordata Ch35 Monday October 19 2015 1000 AM 0 Learning Objectives 0 Understand the adaptations for the invasion of terrestrial habitats by vertebrates 0 Know the significance of the evolution of the amniotic egg 0 Learn amp distinguish the remaining vertebrate classes CLADE Amniotes O Reptiles birds amp mammals are amniotes O Amniotic egg has 4 membranes Fig 352 I Cho on III Outermost layer III Allows gas exchange III Keeps everything contained amp watertight I Amnion III Encases embryo in fluidfilled cavity I Yolk Sac III Provides food I Allantois III Contains excreted waste from embryo CLASSES 0 Class Reptilia I 7000 Species I Occur worldwide except in coldest region due to ectothermia I All living reptiles exhibit 3 key features III Amniotic egg which are watertight El Dry Skin 9 Covers body amp prevents water loss III Thoracic Breathing 9 Increases lung capacity I 2 Important Modern Characteristics III Internal Fertilization 9 Sperm fertilizes egg before protective membranes are formed III Improved Circulation 9 Oxygen is provided to body more efficiently 9 Septum in heart extended in heart extended to create partial wall 0 Crocodiles birds amp mammals have completely divided 4 chamber heart I Ectothermic Obtain heat from external sources III Regulate body temperature by moving in amp out of sunlight III Endothermic Generate their own heat internally 9 Mammals birds ORDERS living I Order Chelonia turtles amp tortoises III Differ from other reptiles because their bodies are encased within a protective shell 9 Carapace dorsal amp Plastron ventral Oct 19th Page 1 El Lack teeth but have sharp beaks El Tortoises are terrestrial while turtles are mostly aquatic El Marine turtles must return to land to lay eggs I Order Squamata Snakes amp Lizards El Paired Copulatory Organs hemipenes in males El Snakes 3000 Species O O 0 Lack Limbs Movable Eyelids External Ears El Lizards 3800 Species 0 Many have ability to regenerate lost tails I Order Crocodylia 25 Species Primarily Aquatic Carnivorous Bodies well adapted to stealth hunting I I I I D O O O 0 Eyes on top of head Nostrils on top of snout Enormous mouth Strong necks Crocodiles 9 Typically Nocturnal 9 Tropical amp Subtropical regions 0 Resemble birds far more than other living reptiles Alligators 0 Only 2 species 0 Class Aves Birds I Most diverse of all terrestrial vertebrates El 28 Orders 166 Families CI 8600 Species I Success lies in unique structure Feather El Feathers likely evolved initially for insulation I Still retain many reptilian traits El Amniotic eggs I Scales on legs I But lack teeth amp tails of reptiles I 2 Major Distinguishing Characteristics El Feathers O O O O 0 Modified scales of keratin Provide lift for flight ConserveInsulate Heat 0 Birds stay very warm Developed from reptile scales Linked structures provide continuous surface amp a sturdy flexible shape I Flight Skeleton 9 Thin amp Hollow Bones 0 Often Fused 0 Provides Rigidity Oct 19th Page 2 ltgt Anchors strong flight muscles I Archaeopteryx1st known bird III Skull with teeth D Long reptilian tail I Adaptations for Flight III Efficient Respiration 0 Air passes all the way through lungs in a single direction III Efficient Circulation 0 4Chambered Heart 0 Muscles receive fully oxygenated blood 0 Rapid Heartbeat D Endothermy 0 Body temperature permits higher metabolic rate 0 Average Temp 4042 C 0 Class Mammalia I 4500 Species III Fewest of species among vertebrate D 3200 species are rodents bats shrews or moles I 2 Fundamental Characteristics D Hair 0 Long keratin rich filaments that extend from hair follicles 0 Insulation camouflage sensory structure protection EX Porcupine III Mammary Glands 0 Females possess mammary glands that secrete milk I Other Characteristics III Endothermy depends on higher metabolic rate 0 4Chambered Heart 0 Respiration using diaphragm III Placenta in most mammals 0 Specialized organ that bring fetal amp maternal blood into 0 Provided embryo with nourishment I Mammalian lineage also gave rise to several adaptations in various groups III Specialized Teeth 0 Different types of teeth to match particular eating habitats 0 Contrast carnivore amp herbivore teeth 0 III Digestion of Plants 0 Herbivorous mammals rely on mutualistic partnership with bacteria for cellulose breakdown III Development of Hooves or Horns 0 Hooves are specialized keratin pads 0 Horns are bones surrounded by keratin ltgt Antlers are made of bone NOT keratin III Flying Mammals Bats 0 Only mammals are capable of powered flight 0 Wing is a leathery membrane of skin amp muscle stretched over 4 ngerbones 0 Navigate in the dark by echolocation Oct 19th Page 3 SUBCLASSES I Subclass Prototheria most primitive I Lay shelled eggs I Only living group is monotremes 9 Monotremes 0 Have a single opening cloaca for feces urinelike reptiles 0 Only 3 Living Species b DuckBilled Platypus b 2 Echidna Species I Subclass Theria El Viviparous young are born from womb not egg 2 Living Clades El Marsupials 9 Major difference us pattern of embryonic development 0 Shortlives placenta 0 After birth it crawls into marsupial pouch latches onto nipple amp continues to develop 9 Kangaroo isolated in Australia 9 Opossum North America I Placental Mammals 9 Produce a true placenta that nourishes embryo throughout its development 0 Forms from both fetal amp maternal tissues 0 Young undergo a considerable period of development before they39re born 9 Includes most living mammals Oct 19th Page 4
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