Stuart S. SumidaBiology 342

(Simplified)Phylogeny of Archosauria

Remember, we’re studying AMNIOTES.

Defined by:

EMBRYOLOGICAL FEATURES: amnion, chorion, allantois, yolk sac.

ANATOMICAL FEATURES: lack of an intertemporal bone.

ALSO, FUNCTIONAL FEATURES: • Costal breathing (inhaling using movement of the ribs).• Active exhalation using movement of ribs to push air out.

ARCHOSAURIA

ARCHOSAURS ARE DIAPSID REPTILES

ARCHOSAURIA INCLUDES:•Crocodylomorpha•Pterosauria•Dinosasuria•Aves (Birds)

Crocodylomorpha Pterosauria Eoraptor Herrerasauridae Saurischia Ornithischia

Archosauria

Alligator mississippiensis

Note presence of bony “scutes” or osteoderms in skin.

Crocodilians are capable of a variety of types of locomotion: swimming; slow-sprawling walk; a moderate speed “high walk;” and even galloping in some young or smaller ones.

PTEROSAURIA:Flying Reptiles of the Mesozoic

They are the closest relatives of dinosaurs, but they are not actually dinosaurs.

They used elongate 4th finger to support a wing.

Reconstruction of the pterosaur Eudimorphodon in pronograde, bipedal walking.

TERMS FOR POSTURE

Pronograde: backbone parallel to ground

Orthograde: backbone perpendicular to ground

BIPEDAL and QUADRUPEDAL are not postural terms.

Pterydactylus

Reconstruction of Pteranodon

Crocodylomorpha Pterosauria Herrerasauridae? Saurischia Ornithischia

Archosauria

Dinosauria

THE MOST PRIMITIVE DINOSAURS

Crocodylomorpha Pterosauria Herrerasauridae Saurischia Ornithischia

THE MOST PRIMITIVE DINOSAURS

A perforate acetabulum

Crocodylomorpha Pterosauria Herrerasauridae? Saurischia Ornithischia

Herrerasauridae:

Upper Triassic of Argentina

2 – 4.5 meters long.

Long, low skull that is as long as the femur.

24 presacral vertebrae; and the vertebrae are relatively shorter than more primitive forms.

Herrerasaurus ischigualastensis

Skull reconstruction

Herrerasaurus ischigualastensis

Reconstruction

24 presacral vertebrae; and the vertebrae are relatively shorter than more primitive forms.

Herrerasaurus ischigualastensis

Dinosaurian groups more derived than Herrerasaurs may be divided into two groups based on hip construction:

SAURISCHIAN ORNITHISCHIAN

(Note position of pubis.)

ORNITHISCHIA

Stegosauria Ankylosauria Pachycephalosauria Ceratopsia Ornithopoda

Thyreophora

Cerapoda

Most ornithischians are herbivores.

Prosauropoda Sauropoda Theropoda

SAURISCHIA

Sauropodomorpha

Eoraptor

Eoraptor lunensis (“Dawn Raptor”)•From the Upper Triassic of Argentina.

•Once thought to be amongst the most primitive of dinosaurs. Now considered to be a primitive Saurischian.

SAUROPODOMORPHAUpper Triassic through end of Cretaceous

Features that define Sauropodomorpha primarily associated with adaptations for herbivory, large size and, later, graviportal locomotion:• Relatively small head• At least ten vertebrae in very long neck.• Teeth coarsely serrated.• Enlarged sacrum• Extremely large thumb with enlarged claw.

More primitive Sauropods

Seismosaurus, a more derived sauropod.

BIPEDAL, Extremely large thumb with enlarged claw.

THEROPODA

•Pronograde bipeds.•Pneumatic (hollow) bones.•Enlarged hand.•Vestigial digits IV and V on hand.•Highly extendable digits I-III on hand.•Compact, elongate, narrow foot – usually missing digit V.

I

IIIII

IV

Theropod Feet: Note missing V.

Coelophysis, skull

Coelophysis: reconstructed in northern New Mexico

THEROPODASauropodomorpha

Coelophysoidea

Abelisauridae

Spinosauroidea

Allosauroidea

Compsognathidae

Tyrannosauroidea

Ornithomimosauria

Oviraptorisauria

Dromaeosauridae

Troodontidae

Avialae

Theropoda

Saurischia

Tetanurae

Coelurosauria

Maniraptora

*

*Ceratosauria

Daspletosaurus

T. rex – Predator or scavenger?

Probably both…

How fast could T. rex really run?

Could it run 25 miles per hour? 40?

Taking animal mass and the strength of both bone and soft tissue into consideration, T. rex tissues and bones would shatter if moving much over ten miles an hour…

For T. rex to be able to travel at 20 m.p.h. the amount of leg muscle mass required to generate that much force would be about 95% to 110% its total body mass. Clearly impossible.

If legs are allowed to account for 40-50% of body mass (very generous), a conservative estimate for “cruising speed” is 11 miles per hour.

THEROPODASauropodomorpha

(?)Eoraptor

(?)Herresauridae

Coelophysoidea

Abelisauridae

Spinosauroidea(?)

Allosauroidea

Compsognathidae

Tyrannosauroidea

Ornithomimosauria

Oviraptorisauria

Dromaeosauridae

Troodontidae

Avialae

Theropoda

Saurischia

Tetanurae

Coelurosauria

Maniraptora

AVIALAE: TRUE BIRDS

Archaeopteryx lithographica