LSC 294 — Dinosaurs

Udo Savalli Home

Lab 9
Prehistoric Reptiles

Synapsids

Pelycosauria Most primitive and reptile-like of the Synapsids Sprawling posture with legs held to side Tail long Some (but not all) had tall dorsal sail Extinct by end of Permian Period (251 mya)	Dimetrodon fossil, Permian Period, North America (MAL1)

Therapsids A paraphyletic group (some are more closely related to cynodonts and mammals) Very diverse forms and lifestyles, inlcuding both herbivorous and carnivorous forms Posture somewhat sprawling (less so than Pelycosaurs) Varied teeth Relatively short tail	Inostrancevia fossil, Permian Period, Russia (AMNH2)

Cynodontia A paraphyletic subgroup of Therapsids that are most closely related to mammals Mostly relatively small and carnivorous Complex teeth with multiple cusps (points) May have been endothermic and with hair?

Mammalia Diverse, with ≈5000 species alive today Have hair (endothermy) Mammary glands provide milk for young Only 2 tooth generations (teeth not continuously replaced) Upright posture with limbs held beneath body During Mesozoic mammals were relatively small, inconspicuous

Palaeosinopa fossil, an otter-like mammal from a now-extinct group; Eocene Epoch (Green River Formation), WY (WDC3)

Parareptilia

Primitive group of exinct reptiles Anapsid skulls that lack temporal openings Quadrupedal Vary from lizard-like, to semi-aquatic to heavy, armored herbivores Turtles were once thought to belong to this group

Captorhinus aguti skull, Permian Period, North America (MAL)

Marine Reptiles

Ichthyosauria Don't seem to be very closely related to any other reptile groups Dolphin-like appearance, with dorsal fin and vertical tail fluke Long, slender snout (some were toothless) Varied considerably in size	Stenopterygius fossil, Jurassic Period, Germany (WDC)

Lepidosauria This group includes modern lizards, snakes, and the tuatara Mosasaurs are a group of Cretaceous lizards related to modern monitor lizards Mosasaurs became fully aquatic and very large Note elongated body and flattened tail, moderate-sized flippers (compare to Pliosaurs)	Halisaurus fossil, late Cretaceous, North America (WDC)

Placodontia Semiaquatic reptiles living near shores Some were lizard-like in shape Many had extensive turtle-like dermal armor Triassic Period only Nothosauria Semiaquatic reptiles with elongated necks and fairly small heads Had webbed feet (instead of true flippers) Intermediate between Placodonts and Plesiosaurs Triassic Period only	Keichousaurus hui fossil, Middle Triassic, China (UMS4)

Plesiosauria Fully marine reptiles Long flippers used for swimming Body relatively short, broad, and stiff, with short tail (compare Mosasaurs) Body shapes range from long-necked and small headed to short-necked and large-headed (Pliosaurs)	Polycotylid plesiosaur skeleton, Cretaceous Period, Morocco (WDC)

Basal Archosauromorphs

Hyphalosaurus lingyuanensis fossil, early Cretaceous Period, China (FMNH5)

Crurotarsi

Phytosauria Large, sprawling, semi-aquatic carnivores Long, slender snout, with nostrils close to eyes Convergently resemble modern crocodiles (and especially gavials)	Leptosuchus skull, Triassic Period, North America (AMNH)

Aetosauria Heavily armored with bony plates covering back, spikes on sides Relatively small head Herbivorous (convergent with Ankylosaur dinosaurs)	Desmatosuchus Skeleton, Triassic Period, Chinle Formation, Arizona (PFNP6)

Rauisuchia The dominant large, terrestrial predators during the Triassic Large heads Crocodile-like armor scutes on back Legs held beneath body; hind legs longer than front (some bipedal?)	Postosuchus Skeleton, Triassic Period, Chinle Formation, Arizona (PFNP)

Crocodylomorpha Includes modern alligators and crocodiles Generally had elongated snouts Back covered in armored scutes Semiaquatic forms (including all moderns species) had an elongated body, flattened tail, and sprawling limbs (secondarily derived) Other forms were terrestrial, with long legs held beneath body Some became fully aquatic with flippers instead of legs	Steneosaurus fossil, early Jurassic Period, Europe (WDC)

Pterosauria

Rhamphorynchoidea Paraphyletic grouping of various primitive forms Long tail that ends in diamond-shaped flag Small-sized	Rhamphorhynchus fossil, late Jurassic Period, Solnhofen Limestone, Germany (MAL)

Pterodactyloidea The more derived clade of pterosaurs Generally larger sized than Rhamphorhynchoids (but size variable) Tail always short Some were toothless	Tapejara skeleton, Early Cretaceous, Brazil (WDC)