EARTH 307: Lecture 20: Reptiles and Birds

Superorder dinosauria

• terrestrial reptiles, some large size

• rarely readapted to aquatic environments

• dominant group of terrestrial organisms almost throughout mesozoic

• Upper triassic (carnian) - cretaceous

• became extinct at cretaceous/paleogene boundary (mass extinction event)

Dinosaur classification

• subdived into 2 orders based on position of pubis bone of pelvic girdle

• Order saurischia (position known from the lizards)

  • pubis is downward and forward

• Order ornitischia (position found in birds)

  • downward and backwards

Order saurischia

• earliest dinos

• bipedal and became quadrupedal

• earliest ones found in southern hemispehere

• most found in south america (argentina and brazil), less frequently found in southern africa (zimbabwe)

• Upper triassic (Carnian) - cretaceous

• earliest ones were insectivores and then carnivorous

• divided into 2 suborders

  • theropoda and sauropodomorpha

Suborder Theropoda

• some were small while some were very big after change in diet

• some were apex predators

• upper triassic (carnian) - cretaceous

Evolution of Flight

• evolution started in late jurassic times

• some small sized ones started to develop features resembling those of birds (preavian theropods)

• began with Archaeopteryx lithographica

Preavians

• started in cretaceous times, new taxa with more evident bird morphological features evolved

• were still reptiles but with strong modified morphology when compared with that of main theropod nexus

Class Aves

• true birds evolved after cretaceous/paleogene mass extinction

• features: disappearance of teeth, toe rearrangement (three to front, one back and loss of fifth), evolution of pneumatic bones, keeled downwards projected sternum, feathers cover most of body surface

• hollow bones helped them fly, feathers stayed the same

Superorder Sauropaodomorpha

• massive quadrupedal reptiles, some over 50tons

• vegetarians but earlier ones were omnivorous

• upper triassic - cretaceous

• from therapods

Order Ornithischia

• vegetarians, less frequently bipedal

• 5 suborders

• ornithopod, Stegosauria, pachycephalosaur, ankylosauria, ceratopsida

• upper triassic (norian) - cretaceous

Suborder Ornithopoda

• early ornitopods were small but later in evolution reached size of 8 m

• bipedal and quadrupedal

• upper triassic (norian) - cretaceous

Suborder stegosauria

• quadrupedal dinos with massive body

• present osteoderms on doral side

• tail can present spike used for defense

• jurassic - lower cretaceous

Suborder Pachycephalosauria

• bipedal dinos with small body in northern hemi

• thickening of skull roof

• Cretaceous

• vegetarian

Suborder ankylosauria

• quadrupedal dinos that evolved bony plates that form dorsal shield

• thickening of tail end which have club like aspect and was used for defense

• cretaceous

Suborder ceratopsida

• quadrupedal dinos that present gradual development of CS with horns used for defense

• earliest representatives lack horns but later developed horns

• upper cretaceous

• youngest groups of dinos