BIOL 329 Lecture Notes - Lecture 13: Gharial, Bipedalism, Ontogeny
6 May 2018
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Lect 13
Archosauria: crocodilla
Appeared in the Triassic or possibly Permian but diversified in Mesozoic.
Bipedalism prevalent in stem groups.
Teeth in sockets, fenestra anterior to the eye and on the lower jaw
Two lineages in the early Mesozoic – crocs vs non-crocs (pterosaurs, dinosaurs, birds)
Mesozoic was period of great croc diversity. Early fossils terrestrial but also invaded aquatic habitats.
Fossils with skulls 2 m in length (12 m body). 3 tropical groups: alligator and caimans / crocodiles /
gharial.
Croc – lower teeth visible with mouth closed
Alligator – lower teeth in upper jaw sockets.
Consumer fish, snakes, birds, mammals. Simple parental care. Ectothermic but have 4 chambered heart
(same as birds and mammals) almost gives them a bit of endothermy.
Crocodiles at the stem of archosaur evolution. Primarily endothermic then reverted to ectothermy when
invading the aquatic predatory niche. Retained a 4-chambered heart (for higher metabolic rate and
blood flow?)
Pterosaurs winged-lizard – originated and extinct in the Mesozoic. Up to 15 m wing. Leather wing
membrane allowed gliding on thermals. Possibly bat-like flight. No keel on sternum for flight muscles
modest. Hollow bones like birds. Landing like birds...
Dinosauria – the three major dinosaur lineages theropods, sauropodomorphs and ornithischians all from
the Triassic. Thermoregulation: thought dinosaurs were ectothermic (large crocodiles). Endothermy
proposed – question link between dinosaurs and birds.
Use radioactive isotopes. High metabolic rates – endothermy may be a synapomorphy. May have been
acquired convergently in the taxa.
Dinosaurs fossils show ontogenetic development of early feathers. Diversity of feathers restricted to
what we found. Ribbon-like feather. Old feathers were more developed than modern ones.
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Document Summary
Appeared in the triassic or possibly permian but diversified in mesozoic. Teeth in sockets, fenestra anterior to the eye and on the lower jaw. Two lineages in the early mesozoic crocs vs non-crocs (pterosaurs, dinosaurs, birds) Early fossils terrestrial but also invaded aquatic habitats. Fossils with skulls 2 m in length (12 m body). 3 tropical groups: alligator and caimans / crocodiles / gharial. Croc lower teeth visible with mouth closed. Alligator lower teeth in upper jaw sockets. Ectothermic but have 4 chambered heart (same as birds and mammals) almost gives them a bit of endothermy. Primarily endothermic then reverted to ectothermy when invading the aquatic predatory niche. Retained a 4-chambered heart (for higher metabolic rate and blood flow?) Pterosaurs (cid:858)winged-lizard(cid:859) originated and extinct in the mesozoic. No keel on sternum for flight muscles modest. Dinosauria the three major dinosaur lineages theropods, sauropodomorphs and ornithischians all from the triassic. Endothermy proposed question link between dinosaurs and birds.
