Triassic Reptiles

Fossil evidence has been found for all of the following in Petrified Forest.

Drepanosaurs, tanystropheids, and Vancleavea

Drepanosaurs are bizarre reptiles are generally small and are known from exquisite specimens from the Triassic limestone quarries in Europe. They may have behaved much like modern chameleons or squirrels;they generally had large, hooked claws on their hands and prehensile, grasping tails. At the park, drepanosaurs are known from these claws and their vertebrae.

Tanystropheids are also small reptiles, but they tend to have extraordinarily long necks that are longer than the rest of the body. Vertebrae from these animals are very recognizable, and we have only recently been finding them in the field.

 
illustration vancleavea emerging from murky water

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Vancleavea
If you saw Vancleavea in the water today, you would think it looked like a fanged and scaly weasel. These aquatic reptiles were covered in bony pieces of armor, which fossilize easily. Vancleavea was about 1.2 m long and was long-bodied and short-limbed. Thirty particularly tall osteoderms formed a vertical fin along the top of the tail.

Vancleavea was named after Phillip Van Cleave, a former Chief Naturalist at Petrified Forest who collected the fragmentary postcranial remains of this small reptile in the early 1960s.

 
Lepidosaurs

What we know about the origins of early lizards and snakes comes from Triassic microvertebrate fossils. Because many of these animals were so small and delicate, most of the lepidosaurs from Petrified Forest are recognized through their teeth, which are implanted on the insides or tops of the upper and lower jaws. Looking for lizard jaws is tedious work; paleontologists must wash bags of rock through sieves of various sizes before spending hours picking out fossils from under high magnification.

 
illustration of long lizard-like animal on branch
Trilophosaurus

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Allokotosaurs

Members of this diverse reptile group include Trilophosaurus and Azendohsaurus. Trilophosaurus is incredibly abundant from the Triassic-age rocks in western Texas. It was a herbivore up to 8.2 feet (2.5 meters) long. It had a short, unusually heavily-built skull, equipped with massive, broad, flattened cheek teeth with sharp, shearing surfaces for cutting up tough plant material. The name "Trilophosaurus" means "three-ridge reptile" and refers to its strange teeth that have three tall crests. Azendohsaurus is known from what is now Madagascar, but a closely related animal once lived at Petrified Forest, as well.
 
fossil embedded in rock
Allokotosaur fossil found in Petrified Forest

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drawing of phytosaur as tall as a human
Smilosuchus

NPS/Jeff Martz

Phytosaurs

Phytosaur fossils are some of the most abundant vertebrate fossils in the park. These long-snouted reptiles are closely related to archosaurs. They look very much like the modern crocodylians, but there are several things that differentiate phytosaurs from crocodylians. First, the nostrils of phytosaurs are located high up on the skull, almost between the eyes! Second, phytosaurs do not have a complete bony roof over the mouth. Third, phytosaurs have a paired row of armor scutes down their back, unlike crocodylians that have multiple rows. Two of the phytosaurs that you would encounter at Petrified Forest in the Triassic are named Smilosuchus and Machaeroprosopus.

 
large skull on table
Phytosaur skull in Petrified Forest's fossil prep lab

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Archosaurs

The "ruling reptiles" of Archosauria rule the fossil record at Petrified Forest. More information can be found on the Pseudosuchian and Orthinodiran archosaur pages. Archosaurs can be differentiated from other reptiles, and from each other, by their ankle structure.

 
diagram drawing comparing ankle bone arrangements
Ankle bones of pseudosuchians (Alligator and Revueltosaurus) compared to an ornithodiran archosaur (Lesothosaurus)

NPS/Jeff Martz

Last updated: April 18, 2016

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Petrified Forest, AZ 86028

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