Mesozoic World: rise of the archosaurs Flashcards
Describe the Mesozoic Era
- post-End-Permian outpouring of the Siberian Traps (252mya)
- pre-end-Triassic Chicxulub impact (66mya).
- “Carnian Pluvial Event” (232mya); temporarily interrupted droughts of the Triassic and released dinosaur diversification
Describe the Archosauria
- diapsids
- dominated the terrestrial environments of the Mesozoic
- replaced the synapsids that had dominated the Palaeozoic
Describe the Mesozoic oceans
diapsid clades rise to dominance
Describe the marine diapsids of the Mesozoic
- ichthyosaurs
- plesiosaurs
- marine turtles
- mosasaurs
Describe marine mesosaurs
became extinct in the Permian.
Describe Ichthyosauria
- marine diapsid
- most specialised
- streamlined body form
- heterocercal tail (convergent with those of sharks)
- viviparity
- oxygen isotope ratios of their tooth phosphate suggest endothermy
Describe the Plesiosauria
- specialised clade of marine diapsid, allied with several other marine clades including placodonts, nothosaurs, and pachypleurosaurs.
- typical body form: four paddle-like fins and a long neck.
- viviparity
- tooth oxygen isotope ratios suggest endothermy
- typical plesiosaur ca. 3m long
Describe modern turtles
- ossified shell
- upper carapace and a lower plastron
- fused to the ribs
- horny beak without teeth
- regionally endothermic
Describe Odontochely
- The Triassic turtle (sc. 220mya) - shallow marine deposits
- full complement of teeth
- no ossified carapace.
- ossified plastron (lower shell evolved before the upper shell as a defense against predation from below
Describe the Archosauria
- greatest of all the diapsid radiations
- crocodiles, pterosaurs, dinosaurs (including birds) and relatives
- derived four-chambered heart: adaptation to active lifestyles
Describe Pterosaurs
- more closely related to dinosaurs than to crocodiles, together forming most of the clade Avemetatarsalia
Avemetatarsalia
all archosaurs more closely related to birds than crocodiles.
Describe modern crocodiles and birds
- four-chambered heart
- derived character of archosaurs
- adaptation to active lifestyles
Describe the Crocodylomorpha
- far greater diversity of body form than living crocodiles
- some fully marine species
- some highly athletic terrestrial forms varying from robust to gracile
List some Crocodylomorpha
- Protosuchus
- Terrestrisuch
Describe Protosuchus
- robust
- ~1m
- Jurassic
Describe Terrestrisuchus
- gracile
- ~0.5m
- Triassic
Describe the specifics of the Pterosauria
- highly-specialized for flight
- earliest known forms (Late Triassic) accomplished fliers
- largest animals ever to fly.
- generally diurnal
- minority may have been at least crepuscular
Describe the Pterosaurian wing
skin membrane stretched between the hyper-elongated 4th finger of the forelimb, and the ankle area of the hindlimb
Describe Pterosaur flight
- smaller pterosaurs used flapping flight
- largest pterosaurs glide long distances while soaring
Describe Pterosaur locomotion
- walked quadrupedally (wing membrane stretched between forelimb and hindlimb)
- unlike that of any extant animal
- plantigrade (“flat-footed”) hindlimb and a digitigrade forelimb (walking on the fingers to accommodate the wing)
Describe the Pterosaur wing
- cruropatagium
- propatagium
- cheiropatagium
- wrist
- steroid
- phalanges of extended wing finger
Describe Pterosaur reproduction
- eggs are rarely preserved
- shell parchment-like (like a snake’s)
- some pterosaurs may have bred colonially, and may have provided care to their offspring (convergent with birds)
- pterosaurs carried two eggs, so retained both oviducts.
Describe Pterosaur thermoregulation
- covered in pycnofibres
- endothermic
Describe pycnofibres
- sometimes branched
- filamentous integumentary appendages
- melanosomes on the head crest suggests they were also used in display
melanosomes
pigmented intracellular organelles
Describe Dinosauria phylogeny
- Ornithischia
- Saurischia
Ornithischia
variety of herbivorous bipeds and quadrupeds
Saurischia
Sauropoda and Theropoda
List some Ornithischia
- Stegosaurus
- Triceratops
- Gastonia
- Parasaurolophus
- Maiasaura
List some Sauropods
- Mamenchisaurus (basal)
- Brachiosaurus
List some therapods
- Allosaurus
- Aves (birds!)
Describe Dinosauria origins
- originated in the Middle Triassic (c. 245mya)
- ecosystems still recovering from the end-Permian mass extinction
- Pangaea
Pangaea
the continents formed the one giant land mass
Describe Dinosauria diversification
- Late Triassic, following the Carnian Pluvial Event (234-232mya)
- climate switched from arid to humid, then back
- Cretaceous break-up of Pangaea isolated the various groups of dinosaur in Laurasia and Gondwana: rapid allopatric speciation
- isolated groups underwent separate, slower adaptive radiations through the rest of the Cretaceous
Describe Dinosauria diversity at the End-Cretaceous
declined sharply during the last 10My
Describe Dinosauria thermoregulation
- last common ancestor of dinosaurs and pterosaurs was endothermic
- ectothermy evolves secondarily in some Ornithischia.
- elevated and relatively stable body temperatures inevitable at very large body size
- long Sauropod necks + air sacs running through vertebrae may have played a role in thermoregulation
Describe small dinosaurs
low growth rates, like modern lizards
Describe large dinosaurs
fast growth rates, like modern precocial birds
Describe Argentinosaurus
- Sauropoda
- 83,000kg
- 40m
- maximum walking speed: 2ms-1
Describe Tyrannosaurus
maximum walking speed of 5ms-1
Describe Dinosauria ventilation
Describe ventilation in modern birds
- lungs connected to balloon- like system of anterior and posterior air sacs
- air sacs act as a pair of bellows, alternately storing air during one phase of the inhalation/exhalation cycle, and releasing it to the lungs during the next phase
- unidirectional flow through the lungs
- much more efficient in gas exchange than tidal flow
- same in non-avian saurischian dinosaurs
Tidal flow
mammalian lungs
Describe Dinosauria reproduction
- oviparous
- carefully arranged their eggs in the nest
Describe Saurodopomorph reproductor
- coloniality
- nest site fidelity
- hydrothermal geyser field for incubation
