Trilobites to T.rex Final Exam Study Guide
Trilobites to T.rex Final Exam Study Guide IFS2087
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Discuss the evolution of birds and flight during the Mesozoic. How do we recognize the first bird? How did flight evolve? • MESOZIC INCLUDES: TRIASSIC, JURASSIC, AND CRETACEOUS • Archaeopteryx is the most primitive bird • We recognize it as the first bird because of the flight feathers • Lived during Jurassic, • Bavaria, Germany – Solenhofen Limestone • Bird bc feathers • DROMEOSAUIDS • Microraptor (EARLY CRETACEOUS) HELPED • Microraptor is a four winged, glossy feathered dromaeosaur from the Early Cretaceous of China. (DROMASAURIDS ARE VERY CLOSE TO BIRDS) • Which lived in the forest and would use their four wings to glide from tree to tree, much like that of a flying squirrel. • In terms of the evolutionary relationship between birds and dinosaurs, Microraptor was a significant discovery. Microraptor’s structure is very similar to the first primitive bird: Archaeopteryx. Also, Microraptor’s ability to climb supports this notion, because dinosaurs that can climb are believed to be more closely related to birds than non-climbing dinosaurs. • Origins of flight • Flight feathers evolved before flight • The terrestrial origin of flight is a more phylogeny based theory that argues that flight must have evolved from the ground, up. • “The ancestors were running dinosaurs, already feathered, probably to conserve body heat. Over time the feathers could have been adapted for flight, as bodies became smaller and the running leaps of dinosaurs evolved into the powered, flapping flight of birds” (Davis, 2008). • However, this theory has its flaws. A common problem brought up by opponents to the ground up theory is that it would always be working against gravity • The arboreal origin of flight theory states that ancestral birds were small tree dwellers that leapt from branch to branch and glided from tree to tree. • As for the ongoing debate about the origin of flight, Microraptor supports the arboreal origin of flight theory (trees down) over the terrestrial origin of flight theory (ground up). T • his support comes from the belief that Microraptor could climb and glide from tree to tree. • Its small size, and its sharp, curved claws made it possible for them to climb up trees • Microraptors are mostly arboreal animals due to the fact that the long feathers on their back limbs made it almost impossible for them to walk comfortably on the ground. • The terrestrial view suggests flight began from the floor up mostly due to a running start. Microraptor could fly, but it couldn’t run, thus weakening that argument. Discuss the evidence for an impact at the end of the Cretaceous and how we came to find it. • Perhaps the most notable event of the Cretaceous was its conclusion. About 65 million years ago the second greatest mass extinction in Earth history occurred, resulting in the loss of the dinosaurs as well as nearly 50% of all the world’s species. Though not nearly as severe as the end-Permian mass extinction, the end-Cretaceous extinction is the most famous mass extinction in Earth history. • The K-T (Cretaceous-Tertiary) extinction is one of the 5 or 6 great mass extinctions in earth history. • • THINGS THAT WENT AWAY • MARINE FOSSIL RECORD • 15% of all marine families • 50% of all marine genera • 80-90% of all marine species • CONTINENTAL FOSSIL RECORD • ~25% of all families • ~56% of all genera • reptiles in general 56% • non-avian dinosaurs 100% • pterosaurs 100% • nothing larger than 25 kg (50 lbs) • Some groups survived relatively untouched - particularly the higher plants and most mammal groups (10 of 15) • WHAT CAUSED IT • All dinos without feaths DIED • India voluanios deccian traps- Happened at the same time • MAYBE THEY CAUSED IT • Possible Causes • Evolutionary Senility • New vegetation • Climatic change • Mammals ate eggs • Disease, poison • Sex change • Sea level change • Supernova • Plate Tectonics • Volcanism- India voluanios deccian traps- Happened at the same time • Ecologic Instability • Asteroid or comet impact- WE GET HIT ALL THE TIME! o FREQUENCY OF IMPACTORS: o Pea-size meteoroids - 10 per hour o Walnut-size - 1 per hour o Grapefruit-size - 1 every 10 hours o Basketball-size - 1 per month o 50-m rock (destroy area size of NJ) - 1 per 100 years o 1-km asteroid - 1 per 100,000 years o 2-km asteroid - 1 per 500,000 years • Lois and Walter Alvarez • In 1980 found Iridium Anomaly in • K-T boundary clay in Gubbio, Italy • Iridium found primarily in cosmic dust, asteroids, comets and earth’s interior • Enough for meteor 10 km diameter • Other evidence: • 10 km meteorite hitting earth @ 70,000 mph – release 200 million megatons. • Vaporize rock & big shock wave • Shocked Quartz and Tektites • Where is the Crater? • Chicxulub in the Yucatan • Results: • Enormous tsunamis that circle the globe • A firestorm in near regions scorched the surface • Dust thrown into the startosphere would have changed the climate into one of "nuclear winter." • Dave Raup and Jack Sepkoski (Univ. Chicago) suggested that mass extinctions might have a significant 26 MY periodicity. • To explain this physicist Richard Muller invented "Nemesis", a hypothetical solar system body with a highly elliptical orbit that took it through the Oort Cloud (source of comets) once every 26 MY and sent a rain of comets into the inner Solar System Discuss the traits that typify a dinosaur and what kind of animal they portray. How did these features set the early dinosaurs apart from their contemporaries? • NON DINOS: ARCHOSAURS – “Ruling Reptiles”=diapsid skulls with antorbital fenestra • ^ Includes Crocodiles, Pterosaurs, Birds, Dinosaurs • What makes dinos different: • Highly regionalized vertebral column with at least 3 sacral vertebrae • Shoulder Joint faces backwards • Digits 4 and 5 on hand reduced • Ilium, ischium, pubis all participate in hip socket (acetabulum) • Acetabulum is open and buttressed • Head of femur (thigh bone) is at right angle to shaft (upright stance) • In ankle, astragulus and calcaneum are reduced and fused to tibia and fibula • Ankle joint is mesotarsal hinge • Metatarsals (foot bones) are elongated and appressed • Stance is digigrade (on toes) • What this all tells us: FIRST DINO was Bipedal, fast running dinosaur, predator How did the terminal Triassic extinction affect the dinosaurs? • They didn’t affect • Everything else died because it needed water How do we recognize a mammal in the fossil record? What do these features have to do with a mammalian lifestyle? • Ear • Jaw joint- mamls have simple jaws • Reptiles have 3 bones • Mamals have diff teeth • Dif teeth require aculsion • To get acclusion- simple jaw joint • Rep smiles big tjings • Rep have more bones in jaw • Old jaw bones are now middle ear bones Discuss the evolution of birds, including timing, ancestors, and the hypothetical origins of feathers and flight. • Arch was in Jurassic • Why did they show up in cretatious? Preservation. • Dromeosaurds • Origin of flight • Discuss the terminal Triassic extinction, what may have caused it, what died, and what effect it had on the rest of the Mesozoic. • NOT PT • CAMP • Related to drying • Dinos didn’t urinate so yay Discuss the lines of evidence for dinosaur metabolism and what they show. Discuss the difference between endo- and ectothermy, homo- and heterothermy, tachy- and bradymetabolic. • Ectotherms obtain body heat from an external source (usually the sun). • Endotherms produce body heat internally. • Describe a behaviour in an ectotherms that is likely to raise its body temperature: o Basking in direct sun • State the effect of an increase in environmental temperature on the metabolic rates of both ectotherms and endotherms o Increase the metabolic rate in ectotherms. o The metabolic rate of endothems is unaffected • Bradymetabolic animals burn energy slowly. o rate of fuel usage is low o slow metabolism o cold-blooded animals • Tachymetabolic animals burn energy rapidly o rate of fuel usage is high o fast metabolism o warm-blooded animals • Homeotherms Temperature remains constant • Heterothermic - of animals except birds and mammals; having body temperature that varies with the environment • Cold-blooded o Ectothermic o Bradymetabolic o Poikilotherm o Fish, amphibians, lizards, snakes • Warm-blooded o Endothermic o Tachymetabolic o Homeotherm o Mammals, birds What was Compsognathus and why is it controversial? • Means delicate jaw • Jaw came apart- never was together • a small theropod which is difficult to classify. • Known only from two specimens from the Upper Jurassic of Europe, Compy may have actually been a juvenile of some other species of theropod. • One specimen preserved with the remains of its last meal, a small lizard • Some believe that it is a close relative of Archaeopteryx • We don’t know how to classify it Discuss the possible advantages and disadvantages of Sauropod necks? • ADV • Reach trees • Put head up and look around • Feeding from a large area • DISADV • Breathing- throat is so long- breath out last time • Stick head up- brain higher than heart- blood flow prob. But they might not mind Were Carnosaurs solitary predators, pack predators, ambush predators or scavengers? What kind of evidence exists? • the largest of the carnivorous Theropods • all > 5m long, large heads, short necks, very short arms, massive legs, long tails • biggest do u need a pack no • hard to hide • scavenger • cant run fast • Solitaty – pray on young adult • Wandered on and if they were hungry they would snap • Much like a lion • They tried to trick Discuss dinosaur growth rates and how we derive them. • We find growth lines in bones • Bones can be resorbed • Bone in leg – fibula- dosent get resorbed in dino • Preserves growth rings in fibulas • Rapidly growing animals = • tachymetabolic • endothermic • homeotherms. • Growth processes • require a lot of energy • work best at a constant temperature • Tyrannosaurus grew very quickly - to full size in about 20 years • However, most rapidly growing animals have a fixed adult size where growth stops. Among living animals, only the slowly growing ectotherms have continual growth. • Growth lines in some dinosaur bones seem to indicate that the adults did not stop growing, just slowed down. • What is EQ, how is it calculated and what does it show? • EQ is used to measure intelligence/brain size. It can tell us which dinosaurs had intelligence more similar to mammals and which were closer to reptiles (helping with endo, ectotherm debates). • Higher EQs often suggest endothermy as extant endotherms burn through more energy to support their active systems (and high brain activity). Lower EQs are more similar to reptiles, which use less power and energy to fuel their systems except in short bursts. • Coelurosaur EQs=cloesr to birds/mammals, • Theropods and Ornithopods slightly less • other dinos closer to reptiles • How its derived • Brain size (Y-axis) vs • Body size (X-axis) • Data for Archosaurs • Plots as line • E = k P 2/ where • E is brain size • P is body size • k is the line slope, • .005 for Archosaurs • EQ is calculated as E /m e • where • E mis measured brain size • E eis brain size expected • from equation E = k P 2/3 • EQ (Encephalization Quotient) comparison for dinosaur endocasts show most dinosaurs had brains no larger than an equivalent-sized Archosaur, with the exception of Carnosaurs and Coelurosaurs, which had larger brains (but only barely as large as comparitive birds or mammals) • We often associate large brains with warm-bloodedness, however the causal connections are not clear. • Mammals and birds tend to have larger brains for a given body size than do reptiles. • Perhaps larger brains are needed to manage the homeostatic mechanisms that contribute to endothermy. • Perhaps large brains require a constant supply of energy consistent with tachymetabolic homeothermy. • We’re not sure what brain size means. • Line refelective of group that related to diff • Higher EQs often suggest endothermy as extant endotherms burn through more energy to support their active systems (and high brain activity). Lower EQs are more similar to reptiles, which use less power and energy to fuel their systems except in short bursts. What are the Fabrosaurids, when did they live, and why are they important? • Fabrosaurids - a Late Triassic - Early Jurassic, small (1-2m.) bipedal ornithischians, often placed within the Ornithopods • Basel orinithistians.. occur early. Look like ornithopods. • Agile herbivore-omnivores living in arid or semiarid regions of US, S. Africa and Argentina. Not an ancestor for all Ornithischians, but with characteristics present in the ancestor. • Small to large (20 m) bipedal herbivores Early Jurassic - Late Cretaceous • No armor • Jaw joint lower than tooth row • Premaxillary teeth (if present) are lower than maxillary teeth • Premaxillary bone has process extending backwards toward eye • Multiple tooth rows • Cheek pouches (tooth row inset from outside of jaw) • True "chewing" • Chewing. • Hypsilophodonts - small to medium-sized (2-4 m) bipedal Ornithopods, Middle Jurassic - Late Cretaceous, N. America, Europe, Asia and Australia • Iguanodontids - large, heavily-built Ornithopods, Late Jurassic - Early Cretaceous; hoof-like tips on toes of hind feet, thumb spike. Iguanodon (10 m) • Head large with long snout and toothless beak. Teeth leaf-shaped with long ridges - resemble those of living Iguanas. • Discuss the Pachyceophalosaurids and how much we know about their anatomy. What did they do with those heads? • Pachycephalosaurs, or "Thick Headed Dinosaurs", are a poorly known group of Ornithischians lumped with the Ceratopsians under the Marginocephalia • Genera include Pachycephalosaurus, Stegoceras, Stygimoloch, and Dracorex. • Most lived during the Late Cretaceous Period, in what is now North America and Asia. • Stegoceras, a small (2 m) dinosaur, is best known example. For Stegoceras, the most complete skeletal information is shown. • The animal appears to be bipedal, with very short fore limbs and a long tail with ossified tendons. • The ilium is long and low. • The vertebrae of the back are ridged so as to "lock" together. • The skull was attached to the neck such that the face hung down with the dome pointed forward. • Teeth are small, slightly curved, compressed and serrated, indicating an herbivorous diet. • The most astounding aspect is the dramatic increase in size and thickness of the skull dome, composed primarily of bone. • Approx.10 other genera, most from very fragmentary fossil material, and are reconstructed by comparison to the few moderately well known examples. • Pachycephalosaurus (big one above) was the largest at 8 m. • Since most are known only from skulls, they differ primarily in size, shape and bony ornamentation of the skull dome. • Two groups are recognized - a primitive group with smaller, flatter domes, and an advanced group with higher domes. • Group is famous as head-butters, this is not universally held interpretation. • The skull dome, although very large and thick (3"+) was also porous and fragile-looking. • It may not have been able to stand up to skull-skull contact the way that modern rams head-butt. • An alternative is that the animals used the dome to flank-butt or just used the size and shape of the dome for species recognition. • They were all bipedal, herbivorous/omnivorous animals with thick skulls. • The adaptive significance of the skull dome has been heavily debated. The popular hypothesis among the general public that the skull was used in head- butting, as sort of a dinosaurian battering ram • Anatomical evidence for combative behavior includes vertebral articulations providing spinal rigidity, and the shape of the back indicating strong neck musculature. • it has been suggested that pachycephalosaurs could make their head, neck, and body horizontally straight, in order to transmit stress during ramming. • However, in no known dinosaur can the head, neck, and body be oriented in such a position. Instead, the cervical and anterior dorsal vertebrae of pachycephalosaurs show that the neck was carried in an "S"- or "U"-shaped curve • The thickened skull of Pachycephalosaurus has led to speculation that males clashed heads with one another in competition for females during breeding season. • Flank butting- like giraffe thing What are the Therizinosaurids and speculate on their mode of life. • Therizinosaurus – Very large Late Cretaceous segnosaur from Asia. Known primarily from arms with 1 m. long claws. • We don’t have a skull yet • Long fingers and claws • Bipedal • Squat and pear shaped • Funky teeth • Funny pelvis- looks ornithistal • Right now- theropods • Unclear what they ate • FISH? • BUGS? TERMITES? o Grizzley bears eat ant • PLANTS? • Dense collections of nests in Gobi desert and mono-specific bone beds suggest gregarious behavior. Analysis of brain casts suggests well developed sense of smell and balance. What are the Ornithomimids and what do we know about their body covering and life habits? • Coelurosaurs – generally smaller, bird-like Theropods • Include Tyrannosaurs, Oviraptors, Ornithomimids, Dromaeosaurs (Raptors), Troodontids, Birds • Ornithomimids – “Bird Mimics” Late Cretaceous N. Am & Asia • Include Struthiomimus and Gallimimus • Resemble flightless birds like emus. • Reduced dentition/beak • Long arms and tail • Long legs • Light skulls • Big eyes, short snout • Very long neck • Belly ribs and back ligaments • Probably omnivorous • Paleontologists believe that ornithomimids were the fastest dinosaurs that ever lived, some long-legged varieties (such as Dromiceiomimus) capable of hitting speeds of 50 miles per hour. • There's also a strong temptation to picture ornithomimids as covered with feathers, though the evidence for this isn't as strong as for other families of theropods, such as raptors and therizinosaurs. • The most unusual characteristic of ornithomimids was their omnivorous diets. • These were the only theropods we yet know of, besides the therizinosaurs, that evolved the ability to eat vegetation, as evidenced by the gastroliths found in the fossilized guts of some specimens. • Since later ornithomimids had weak, toothless beaks, it's believed that these genera fed on insects, small lizards and mammals as well as plants. • May not have been a true carnivors • Covered in feathers- not flight feathers Discuss the unique features of the Dromaeosaurs and what these features tell us about their life styles. • Dromaeosaurs – (AKA Raptors) Cretaceous N. Am & Asia • includes: Deinonychus, Velociraptor, Utahraptor • Small coelurosaurs with • large skull • teeth serrated on both edges • long arms • long 3-fingered hands • Small coelurosaurs with ossified tendons in tail • large claw on 2 toe • must run on 2 toes • Agile, lightly built, and fast-running, these theropods were among the most effective predators of their time. • ll dromaeosaurs were bipedal, and the second toe of each foot was extremely flexible and bore a specialized killing claw, or talon, that was not used in walking. • instead, it was always held off the ground because it was much larger and was jointed differently from the other claws. • Dromaeosaurs had large heads equipped with many sharp serrated teeth, and their long arms ended in slender three-clawed hands that were used for grasping. • Like troodontids and birds, dromaeosaurs had a unique wrist joint that allowed the hands to flex sideways. This evidently helped them seize their prey; in birds the same motion produces the flight stroke. • The tails of dromaeosaurs were also unusually long and were somewhat stiffened by bundles of slim bony rods that were extensions of the arches of the tail vertebrae. • Dromaeosaurs apparently ran down their prey (probably small- to medium- sized herbivores), seizing it with the front claws while delivering slashing kicks from one of the taloned hind legs. • In doing so, dromaeosaurs may have been able to hold this one-footed pose by using the rigidly outstretched tail as a counterbalance, or they may have attacked by using both feet in a single leaping action. • The relatively large brains of dromaeosaurs enabled them to carry out these complex movements with a degree of coordination unusual among reptiles but quite expected in these closest relatives of birds. • Fossil evidence supporting the prediction of grasping arms and slashing foot claws was borne out by the discovery in the 1970s of a Velociraptor preserved in a death position with a small ceratopsian dinosaur, Protoceratops. The hands of Velociraptor were clutching the frill of Protoceratops, and the large foot claw was found embedded in its throat. Explain how Oviraptors got their name and why it may be undeserved. • One day the expedition photographer, James B. Shackleford, discovered a plant-eating dinosaur called Protoceratops . Later a technician named George Olsen found a nest of eggs close by that contained the bones of another dinosaur on top of the nest. He assumed that the eggs belonged to Protoceratops , but the bones associated with this nest were those of a meat- eating dinosaur. Because Protoceratops was a plant eater, he concluded that this new, previously unknown, dinosaur was stealing the Protoceratops eggs from the nest, and because of this it was named Oviraptor, which means egg thief. • Many years later Dr. Philip Currie and a team of paleontologists uncovered another nest in Inner Mongolia and surprise, it contained Oviraptor bones on top of the nest as well. Another Mongolian expedition the following year even found parts of a tiny baby dinosaur skeleton (embryo) inside the same kind of egg. When they began to study these embryos they were surprised to learn that they were actually from an Oviraptor, and not Protoceratops . • This discovery completely changed the world's view of Oviraptor. Dr. Currie and many other dinosaur hunters believe that the adult that was found with the nest was actually a mother or father Oviraptor sitting on the nest, much like a mother chicken does, to protect the eggs. Mongolia has very bad sandstorms, so it is now thought that the mother was protecting the eggs during a severe sandstorm that buried them. Dr. Currie and other scientists believe that this discovery is strong evidence that Oviraptors were excellent parents and that they cared for their young, much like modern birds. Discuss feathers on dinosaurs, which groups are known to have had them and what they were used for. • Theropods • Ornithistians- statisaurous- hair like feathers on tail • If that’s the case they all had them. • We’ve known for decades that many non-avian dinosaurs had feathers. But evidence of plumage usually shows up within a very specific group, namely theropods—or “meat-eating” dinos—such as Velociraptor. However, Tianyulong and other heterodontosaurids were ornithopods, a clan which represents a very different branch of the dinosaurian family tree. Because such distantly-related animals have been found with somewhat similar coverings, it seems likely that feathers started evolving at a very early point in dinosaur history. • Feathers can be used for many things like • Camouflage • Mate selection • Warmth • What are Pterosaurs, how are they related to dinosaurs, and how might they have evolved? • Pterosaurs (meaning "winged lizard") were flying reptiles of the clade or order Pterosauria. • They existed from the late Triassic to the end of the Cretaceous Period (228 to 66 million years ago) • Pterosaurs are the earliest vertebrates known to have evolved powered flight. • NOT DINOS - A pterosaur is no more a dinosaur than a goldfish is a shark. • They are missing a few chararistics- so close. • Appear • Members of ARCHOSAURS – “Ruling Reptiles” • diapsid skulls with antorbital fenestra • What was Archaeopteryx and where was it found? Discuss those features which make it a missing link. • Archaeopteryx is the most primitive bird • Jurassic, Bavaria – Solenhofen Ls • Because it has flight feathers it is a first bird • Because it displays a number of features common to both birds and non- avian dinosaurs, Archaeopteryx has often been considered a link between them. • Everything else makes it dino • Dino head with teeth • Raptor wings • Despite their small size, broad wings, and inferred ability to fly or glide, Archaeopteryx had more in common with other small Mesozoic dinosaurs than with modern birds. In particular, they shared the following features with the dromaeosaurids and troodontids: jaws with sharp teeth, three fingers with claws, a long bony tail, hyperextensible second toes ("killing claw"), feathers (which also suggest warm-bloodedness), and various features of the skeleton. • These features make Archaeopteryx a clear candidate for a transitional fossil between non-avian dinosaurs and birds. How are the Stegosaurs and Ankylosaurs related and how do their geologic ranges compare? • Jurassic- solidisaurs an ornothis herb quadapedal had plates in back • ^ common ancestors • Stegosaurs first in Jurassic • toward end they fade • cretaceous Ankylosaurs pop up. What is unique about the teeth/skull of the Hadrosaurs and how would this affect their life habit? Discuss potential impact on vegetation. • NOT HADRO: In general, dinosaur jaws and teeth were for cutting, plucking, and tearing. Dinosaurs didn’t chew their food, but instead ripped or clipped their morsels, which were then swallowed whole. BUT HADROSAUR WAS DIFF IT COULD CHEW ONE OF THE FIRST • Hadrosaurids, "duck-billed" dinosaurs, large (7-10 m) Ornithopods Middle – Late Cretaceous . • Hadrosaur jaws had 3+ replacement teeth for tooth location. • Chewing was achieved as in the Hypsilophodonts. • Cheek teeth packed into "dental battery" for grinding. • Hadrosaursids divided into 2 groups: • Hadrosaurines - flat skull roofs and long nasal bones ("Roman-nosed" hadrosaurs), • Lambeosaurines - convoluted tubes and crests on top of the skull ("Crested" hadrosaurs) • The crests may have been used for visual display or for producing distinctive calls. • How are the Ceratopsian and Hadrosaur teeth similar? Different? What were the purposes of the Ceratopsian frills/horns? Evolutionarily when did these develop? How might they have caused us to over-split Ceratopsian species? What is peculiar about Microraptor and what bearing does it have on the evolution of birds? • 4 wings!!!!! • The Microraptor is a small, four winged, dromosaurid theropod found in China in the early 2000s • Very small. smaller than the Archaeopteryx. • Similar to Archaeopteryx. • Dromaeosaurids are a subgroup of the group Coelurosauria and of the theropods. These dinosaurs were intelligent, small, large-eyed, fast, bipedal, efficient killers that were closely related to birds • Ability to climb • Helps terrestrial origin of flight hypothesis i • Vital to TOF is that fast running, winged dinosaurs were fundamental in the origin of flight. • However, the fourteen very long pennaceous feathers attached to the metatarsus on Microraptor gui make it hard to say that the small dinosaur had any limbs adapted for running. • In fact, the long feathers on the feet would be a burden on a small cursorial, or having limbs adapted to running, animal. • So, it is very unlikely that Microraptor could walk, let alone run at all. What was Maiasaurus and what evidence do we have for it’s behavior? • Maiasaurus ("Good Mother Lizard") discovered by John Horner, discovered nests in Montana in 1978. Spacing of the nests and age of fossilized young preserved in the nests indicate communal nesting grounds and that young were cared for in the nests for several months after hatching. • Large accumulations of single species in fossil deposits, especially over 10,000 individuals of Maiasaurus in a single deposit (associated with a volcanic ash fall) supports herding, and possibly migratory behavior. • Late Cretaceous fossils north of the arctic circle suggest long distance migration. • Depressions that are supposed to be nests • Diff in color related to oxy available • Inside dnt have much oxg • Lined nest with veg material • Rotting veg generates heat • ^aligators do this • egg shell and bones of young in nest • anal size of bones • young were several months old • mom was bringing food- bc why else would they still be there • spacing of the nests- 1 body legnths of an adult apart • suggesting that it was communal • Jack may have over interpreted • Skeptical interp- the evidence when viewed could be skep
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