The Mesozoic World & Rise of the Archosaurs Flashcards
What two major mass extinctions book end the Mesozoic Era
End-Permian (252 mya): Triggered by Siberian Traps volcanism
End-Cretaceous (66 mya): Caused by Chicxulub asteroid impact
What two significant extinction events occurred within the Mesozoic
Carnian Pluvial Event (232 mya): A wet period interrupting the Triassic droughts, enabled dinosaur diversification
End-Triassic Extinction (202 mya): Paved the way for further dinosaur dominance
Which clade rose to dominance in the Mesozoic, replacing synapsids
Diapsids, including marine and terrestrial groups
What are the three dominant marine diapsid groups of the Mesozoic
Ichthyosaurs
Plesiosaurs
Marine turtles
What features suggest that ichthyosaurs were endothermic
Streamlined body, live birth, and oxygen isotope data from tooth phosphate
What does Odontochelys tell us about turtle evolution
It had an ossified plastron but not a full shell, suggesting the lower shell evolved first—likely as protection from below
Which animals are included in Archosauria
Crocodiles, pterosaurs, dinosaurs (including birds), and their relatives
What is Avemetarasalia
The clade including all archosaurs more closely related to birds than to crocodiles (includes pterosaurs and dinosaurs)
What does a four chambered heart in modern birds and crocodiles suggest
That archosaurs ancestrally had a four-chambered heart, supporting active lifestyles and efficient metabolism
What is Euparkeria and why is it significant
A Middle Triassic archosauromorph; sister taxon to Archosauria
Had a fenestra for muscle expansion and socketed teeth (strong bite)
Featured a calcaneal tuber for a more erect gait
How diverse were early crocodylmorphs
Extremely - ranged from marine species to highly athletic terrestrial forms, much more varied than modern crocodiles
How was the pterosaur wing structured
Membrane stretched from hyper-elongated 4th finger to the ankle
What do pterosaur trackways and reproductive traits suggest
Walked quadrupedally
May have bred colonially and cared for young
Retained both oviducts (unlike birds)
How did flight styles differ among pterosaurs
Small pterosaurs: flapping flight
Large pterosaurs: likely gliding flight
What was the first dinosaur known to science
Megalosaurus, a bipedal carnivorous theropod
What defines Dinosauria as a clade
Perforate acetabulum (hip socket)
Interned head of femur
What are the two major clades within Dinosauria
Ornithischia: Herbivorous bipeds/quadrupeds
Saurischia: Includes Sauropoda and Theropoda
When did dinosaurs first appear
Middle Triassic, during ecosystem recovery after the end-Permian extinction
What event triggered the Late Triassic diversification of dinosaurs
The Carnian Pluvial Event (~232 mya)
How did the breakup of Pangaea influence dinosaur evolution
Isolated populations → allopatric speciation → adaptive radiations
What marks the beginning of the decline of Dinosaurs
A sharp decline in diversity during the last 10 million years of the Cretaceous (though fossil record may be incomplete)
How did growth rates vary among dinosaurs
Small dinosaurs: low growth rates like modern lizards
Large dinosaurs: rapid growth rates like modern precocial birds
What does recent analysis suggest about thermoregulation in dinosaurs
The common ancestor of dinosaurs and pterosaurs was likely endothermic; ectothermy re-evolved in some Ornithischia
What respiratory system do birds and non avian saurischian dinosaurs share
Lungs connected to anterior and posterior air sacs
Unidirectional airflow through lungs
More efficient gas exchange than mammalian tidal flow
