Rise of the Archosaurs Flashcards
Which two extinction events began and ended the Mesozoic?
Start- end-Permian Extinction- Outpouring of the Siberian Traps (252mya)
Finish- end-Cretaceous Extinction- Chicxulub impact (66mya)
What are two other major events that occurred during the Mesozoic?
- Carnian Pluvial Event (232mya)- interruption of Triassic droughts which increased dinosaur diversity
- end-Triassic Extinction (202mya)
Archosaurs are members of which clade?
Diapsids
The Marine Diapsids included which 4 groups?
- Ichthyosaurs
- Plesiosaurs
- Marine turtles
- Mosasaurs
What key convergent trait did ichthyosaurs share with sharks
Heterocercal tail- lobes of tail are of different lengths
What key adaptations to marine life did ichthyosaurs and plesiosaurs share?
- Viviparity
2. Endothermy
What two features of modern turtles did Odontochelys, a Triassic testudine, lack?
- Ossified carapace
2. Horny beak
Which part of the shell first ossified in testudines?
The lower shell (plastron), suggesting an ossified shell was used for protecting from attacks from below.
Dinosaurs and pterosaurs form which clade?
Avemetatarsalia (All archosaurs more closely related to birds than crocodiles)
What trait do only crocodile and birds (archosaurs) possess amongst the modern diapsids?
4-chambered heart, reflecting the active lifestyle of archosaurs
What are the diagnostic characteristics of archosaurs?
- Powerful bite (teeth in sockets, antorbital and mandibular fenestra accommodating large muscles)
- Modified ankle joint with calcaneal tuber, allowing for more upright gait.
How did Mesozoic Crocodylomorphs differ from modern crocodiles?
Much greater diversity of body form, ranging from fully marine, to athletic terrestrial builds.
Biomechanics modeling suggests pterosaurs had what form of unique terrestrial locomotion?
Walking with a plantigrade (“flat-footed”) hindlimb and a digitigrade forelimb (walking on the fingers to accommodate the wing).
What traits of pterosaur reproduction are indicated by current fossil evidence?
- Parchment-like egg shells, like snakes
- Colonial breeding
- Care for offspring after birth.
What were the filamentous integumentary appendages (like downy feathers) coating many pterosaurs called?
pycnofibres
What are the defining features of the Dinosauria?
- Perforate acetabulum forming hip joint
- in-turned head of femur
(Both associated with upright and bipedal stance.)
Which two clades are dinosaurs traditionally believed to fall into?
- Ornithischia (herbivorous bipeds and quadrupeds)
2. Saurischia (Sauropoda and Theropoda)
When did the dinosaurs first appear?
Middle Triassic (c.245mya)
How did the splitting of Pangea into Laurasia and Gondwana during the Cretaceous impact the dinosaurs?
Promoted rapid allopatric speciation.
What trend can de seen in dinosaur diversity in the last 10 mya of the Cretaceous?
Sharp decline
What form of thermoregulation did many large dinosaurs employ?
Gigantothermy- body temperature remains high and relatively constant due to huge size.
What were the purposes of air sacs in Sauropod vertebrae?
- Thermoregulation
2. Regulation
How did the growth rates of large and small dinosaurs vary?
- Large dinosaurs had fast growth rates like modern precocial birds.
- Small dinosaurs grew slowly, like modern lizards.
What maximum walking speed does biomechanics analysis suggest for Tyrannosaurus?
5 m/s
What is the purpose of anterior and posterior air sacs in modern birds (and non-avian saurischian dinosaurs)
Unidirectional flow (deoxygenated air does not need to pass back through the lungs.)
What characteristic traits of avian reproduction originated in non-avian dinosaurs?
- Coloniality
- Brooding
- Site fidelity
- Shell pigmentation
What was the first non-avian dinosaur with feathers to be discovered?
Sinosauropteryx
Why is integument (feather-like appendages) likely to have been an ancestral feature of the clade Avemetarsalia?
Similarities between pycnofibres and simple therapod feathers.
Why are non-avian feathered dinosaurs likely to have coexisted with birds?
Many non-avian feathered dinosaurs are younger than Archeopteryx, which is often considered to be the earliest known bird.
