Phytosauria
|
Pseudosuchia is the clade that includes all crocodile-line Archosaurs (archosaurs more closely related to crocodiles than to dinosaurs or birds). The most basal group in the clade are the Phytosaurs (a misleading name meaning plant lizard since the first fossil found had damaged teeth was thought, incorrectly, to be an herbivore). Phytosaurs look remarkably like modern crocodylians, with elongated bodies, sprawling posture, laterally-flattened tail and long snouts, but they evolved these features independently as the crocodylians of the time were very different terrestrial animals.
This Redondosaurus sp. skeleton is a composite derived from bones of 6 individuals.
Bull Canyon & Redonda Formations, Chinle Group, New Mexico
Late Triassic Period, 205 Ma
New Mexico Museum of Natural History & Science
|
|
|
|
Dorsal view of a Machaeroprosopus (formerly Pseudopalatus) sp. skull and mandible. The external nares (nostrils) are located on the forehead, which distinguishes phytosaurs from modern crocodylians which have their nostrils at the tip of the snout.
Bull Canyon Formation, Chinle Group, Quay Co., New Mexico
Late Triassic Period
New Mexico Museum of Natural History & Science
|
|
|
|
The skulls of Machaeroprosopus show considerable variation even in a single locality (compare to example above). This may reflect several closely related species in the same area or could indicate sexual dimorphism.
Bull Canyon Formation, Chinle Group, New Mexico
Late Triassic Period
New Mexico Museum of Natural History & Science
|
|
|
|
Phytosaurs, like modern crocodylians, were semi-aquatic ambush predators that ate a variety of vertebrate prey. This skull is from Leptosuchus crosbiensis.
late Triassic Period
Arizona Museum of Natural History
|
|
|
|
Angistorhinus sp.
Colorado City Formatiom, Chinle Group; New Mexico
Late Triassic Period
New Mexico Museum of Natural History & Science
|
|
|
Aetosauria
|
Aetosaurs were heavily armored herbivores with dorsal bony plates and in some cases, spines. They had small heads ending in an upturned snout.
This is Desmatosuchus haplocerus
Chinle Formation; Arizona
late Triassic Period
Petrified Forest National Park
|
|
|
|
A complete but somewhat distorted fossil (cast) of Typothorax coccinarum. The skull is at the right. The apparant hump is dorsal armor that would normally sit flat on the back. The front legs are pressed against the body and not as easily distinguishable.
Bull Canyon Formation, Chinle Group, Quay Co., New Mexico
Late Triassic Period, 220 Ma
New Mexico Museum of Natural History & Science
|
|
|
|
Revueltosaurus callenderi is a small (1 m long) ancestral relative of the aetosaurs. It had some dermal armor, but its extent and arrangement is not known.
Chinle Formation; Arizona
late Triassic Period
Petrified Forest National Park
|
|
|
|
These tracks have been named Brachychichirotherium. The actual maker of these tracks is unknown, but they probably belong to an Aetosaur.
Moenave Formation, St. George, Utah
Early Jurassic Period
Dinosaur Discovery Site, Utah
|
|
|
Rauisuchians
|
Rauisuchia is a paraphyletic grouping of pseudosuchians between the Aetosaur and Crocodylomorph branches. They are mostly (with some exceptions) large-headed predators. Some were probably bipedal.
This reconstruction of Postosuchus kirkpatricki is out of date, as a recent study determined that the font legs were smaller (this reconstruction is based on a composite from multiple individuals) and thus it was likely bipedal.
Chinle Formation, Arizona
late Triassic Period, 228-202 Ma
Petrified Forest National Park
|
|
|
|
Life model of Postosuchus kirkpatricki
Taxonomy: Archosauromorpha; Pseudosuchia; Rauisuchia
Late Triassic Period, 225 Ma; Arizona
Arizona Museum of Natural History
|
|
|
Crocodylomorpha
|
The Crocodylomorpha includes all living crocodylians as well as their extinct relatives that are closer to crocodiles than to Rauisuchians. The crocodylomorphs as a whole were morphologically much more diverse than the surviving modern species. The earliest forms were relatively small, terrestrial, and with long legs held beneath the body.
Life model of Protosuchus sp., a typical early, terrestrial crocodile ancestor.
Taxonomy: Archosauromorpha; Pseudosuchia; Crocodylomorpha; Protosuchidae
Early Jurassic Period
Dinosaur Discovery Site, St. George, Utah
|
|
|
|
Life model of Fruitachampsa sp., another terrestrial crocodylomorph.
Taxonomy: Archosauromorpha; Pseudosuchia; Crocodylomorpha; Shartegosuchidae
Late Jurassic Period, 149 Ma; Colorado
Arizona Museum of Natural History
|
|
|
|
There are a number of distinctive subgroups of crocodylomorphs. One such group is the Notosuchia (southern crocodiles), a group that was mostly restricted to the southern hemisphere. They were terrestrial, with an upright posture (legs held beneath body), and had diverse diets and lifestyles.
Fossil of Araripesuchus patagonicus, a dog-sized predatory notosuchian.
South America
Cretaceous Period
Fernbank Museum of Natural History, Georgia
|
|
|
|
This Tsoabichi greenriverensis caiman is a good example of a modern crocodylian (Clade Neosuchia). It is a fairly small (<1m long) semi-aquatic predator with a sprawling posture and laterally compressed tail.
Green River Formation, Wyoming
Eocene Epoch
Black Hills Institute Museum, South Dakota
|
|
|
|
Borealosuchus sp was a mid-sized crocodile reaching up to 3 m long.
McCone Co., Montana
Eocene Epoch
Museum of the Rockies, Montana
|
|
|
|
Deinosuchus riograndensis (skull cast) was one of the largest crocodylians ever, and most likely ate dinosaurs. It is closely related to modern alligators. (The small white skull is a modern crocodile skull for scale.)
Aguja Formation, Big Bend area, TX
Late Cretaceous Period, Campanian Stage, 84-69 Ma
Black Hills Institute Museum, South Dakota
|
|
|
|
Leidyosuchus sp. skull.
Cloverly Formation, Montana
Late Cretaceous Period
Black Hills Institute Museum, South Dakota
|
|
|
|
Stangerochampsa sp. is a small crocodylian related to alligators.
Hell Creek Formation, Carter Co., Montana
Late Cretaceous Period, 66 Ma
Dinosaur Resource Center, Colorado
|
|
|
|
Goniopholis sp. is a semi-aquatic crocodylomorph that is near the base of the Neosuchia (the group that is more closely related to modern crocodiles than to the notosuchians).
North America, Eurasia
Late Jurassic to early Cretaceous Periods
Museum of Ancient Life, Utah
|
|
|
|
Terminonaris robusta had a long, slender snout used to capture fish, much like the modern gharials.
Carbon Co., Montana
Cretaceous Period, 93 Ma
Museum of the Rockies, Montana
|
|
|
|
Dyrosaurus sp.
Morocco
Eocene Epoch, 50 Ma
Wyoming Dinosaur Center
|
|
|
|
Sarcosuchus imperator was another giant neosuchian crocodylian capable of eating dinosaurs, although it is less closely related to the mondern crocodylians than is Deinosuchus (seen in the background here; the white skull is a modern crocodile for scale).
Tegana Formation, Morocco
Cretaceous Period, Albian/Cenomanian Stage, 110-90 Ma
Black Hills Institute Museum, South Dakota
|
|
|
|
Life model of Pristichampsus sp., a true crocodile, but one that was nonetheless mostly terrestrial.
Taxonomy: Archosauromorpha; Pseudosuchia; Crocodylomorpha; Pristichampsidae
Eocene Epoch
San Diego Natural History Museum
|
|
|
|
Macrospondylus bollensis (formerly in the genus Steneosaurus) was a primitive member of the Thalattosuchia, the marine crocodiles. While most thalattosuchians were fully aquatic, with flippers and a tail fluke, Macrospondylus was only semi-aquatic, similar to other crocodylians.
Europe
Early Jurassic Period, 195 Ma
Wyoming Dinosaur Center
|
|
|
|
