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Herpetology Midterm Notes


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Herpetology Midterm #2
Reptile Evolution
Ornithosuchia- bird crocodiles
Pseudosuchia- false crocodiles, this group contains modern crocodiles
Crown Group- the most recent common ancestor of at least two extant groups
and all its descendants
Ornothischia- bird hipped dinosaurs, herbivorous dinosaurs
Saurischua- lizard hipped dinosaurs, carnivorous and herbivorous
- Archosaurs were considered the ruling reptiles, were diapsids, and originated
approx. 250 mya in the late Permian, just after the Permian extinction
- gave rise to the pterosaurs, crocodiles, and dinosaurs
- varied in size from that of a small passerine to the size of airplanes
- dominated in the Jurassic and Cretaceous
- were the largest vertebrates to ever take to the air, were gliders and not fliers
- early pterosaurs (late Triassic, extinct by end of Jurassic) had long tails and
their ancestors had shorter tails (late Jurassic to end of Cretaceous)
- recent evidence suggests that the largest pterosaurs had the ability to maintain
powered flight based on their skeletal structure
- pterosaurs had hollow bones, large brains with well developed optic lobes, and
several crests on their bones to which flight muscles attached
- all consistent with powered flapping flight
- most likely did use warm air currents to soar and maintain altitude
- commonly used by birds with large wingspans
- first arose approx. 200 mya
- modern crocodiles have changed very little from their ancestors
- the earliest crocs were small, terrestrial, two-legged sprinters, and some were
even vegetarians
- originally embraced forms dating from the late Triassic to the present
- by the start of the Jurassic period (150 mya) crocs had mostly abandoned their
terrestrial lifestyles
- we begin to see the marine adaptations like those of modern crocs and
alligators: long bodies, splayed limbs, and narrow, flat, tooth-studded snouts
with powerful jaws (a necessary innovation, since crocs feasted on dinosaurs
and other animal that ventured too close to the water)

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- about 100 mya, toward the middle of the Cretaceous period, some crocs
became enormous
- Sarcosuchus, dubbed “SuperCroc” , measured 40 feet long from head to tail
and weighed around 10 tons
- modern crocodilians: crocodiles, alligators, and caimans
- salt water crocs: 21ft long, 1 ton (largest)
Dinosaur Evolution
- the first recognized dinosaurs are believed to have arisen approx. 230 mya
- Eoraptor was small, 20 lb., 3 ft long, reduced forelimbs, 5 digits
- the first dinosaurs were small, bipedal predators
Saurischians are divided into therapods and sauropods
- includes ornithopods which were small 2-legged herbivores
- most were small, had 3 or 4 toed feet
- recent discovery of 2 new genera with members weighing 5-6 tons
- duck billed dinos lived during the middle to late Cretaceous, so,e believe they
lived in herds
- thick,squat torsos, massive, inflexible tails, and tough beaks and numerous
cheek teeth designed for breaking down tough vegetation
- may have had webbed feet or pads similar to camels, stiff tails, walk on 4 limbs
or run on 2, largest weighed 20 tons
- migrated to nesting grounds to reproduce, nasal crest may have been a
resonating chamber for sound production
- Hadrosaurs, such as Edmontosaurs, were large, 13m long, lived 73-65 mya,
migrated between Alberta and Alaska, preyed upon by T-rex
- early Jurassic to 65 mya, armoured, had spies and some had clubs for defense
- stocky, low slung, short legged, and probably very slow quadrupeds that spent
their days grazing on low-lying vegetation
- 30 ft long and weighed 5 tons
- lived from 160-65 mya
- were herbivorous, four-legged, elephant like dinos whose enormous heads
supported elaborate horns and frills
- horns could be used to fend off predators or to intimidate rival males
- frills could make a ceratopsian look larger to predators and could be a deterrent

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- frills may attract the opposite sex and possible dissipate or collect heat
- a recent study concludes that the main factor driving the evolution of horns and
frills was the need for members of the same herd to recognize each other
- very large, Triceratops was 30 ft long and weighed 5 tons, arose 70 mya and
was one of the last Ceratopsians to be derived,
- complete Triceratops skulls have become prized items at auctions worldwide,
fetching millions of dollars from wealthy bidders
- the other group of herbivorous dinos
- this group contains the largest dinosaurs that ever walked the planet
- large, four legged, plant eating dinosaurs with bulky trunks, long necks and
tails, and tiny heads with small brains
- arose about 200 mya and gone 65 mya, but scientists believe numbers slowly
declined during the Cretaceous before the extinction
- Yizhousaurus is believed to be the first sauropod and was discovered in China
2010, 200 mya
- adults had to consume hundreds of pounds of plants and leaves every days
- two basic kinds of teeth: either flat and spoon shaped, or thin and peg-like
- believed to have evolved their ultra long necks in order to reach the high leaves
of trees
- required and immensely strong heart
- although these are the largest animals to have ever lived only incomplete fossils
have ever been found
- Argentinosaurs lived approx. 100 mya, 130 ft long and 110 tons
- Brontosaurus=> Apatosaurus (was discovered first)
- beast-footed
- were obligate bipedal and some were the largest carnivores to roam the Earth
- birds are the descendants of small theropods
- hollow, thin walled bones
- three main digits on the hand elongated and having claws, the fourth and fifth
digits are reduced
- same for the foot except the first and fifth were reduced
- had sharp recurved teeth indicating they were carnivores
- their clavicles fused into a wish bone
- intramandibular joint between the dentary and post dentary bones which
absorbs the stresses from struggling prey in their jaws
- carnivores were outnumbered by herbivores since it takes a larger number of
herbivores to support a carnivore population
- believed that theropods hunted in packs to take down the large herbivores
- earliest theropods are believed to be the Herrerasaurus from the late Triassic

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