Reptiles and Dinosaurs
of Arizona

The reptiles and dinosaurs that roamed Arizona did so during the Mesozoic Era or the Age of Reptiles, which began 245 million years ago and ended 65 million years ago. This era consists of three distinct periods, the Triassic Period, Jurassic Period and Cretaceous Period.

The Triassic Period
(245 million to 208 million years ago)

Poposaurs

This species has been found in the Petrified Forest National Park. They reached six to sixteen feet in size and were the largest land dwelling predator at that time. Three separate species of this family have been located.

Aetosaurs

At a length of six to thirteen feet, these animals have also been found in New Mexico and Texas. Solidly encased in armored plates, they resembled an armadillo. They were herbivores and all five Arizona species were found in the Petrified Forest National Park which at the time was very tropical or perhaps semi-tropical.

Phytosaurs

The phytosaurs found represent nine species and reached from six to thirty feet in length. Though generally larger, they resemble modern day crocodiles but are considered their predecessors rather than their ancestors. They were the most numerous vertebrates in the Petrified Forest National Park and lived in and along the water. Phytosaurs became extinct at the end of the Triassic period likely because of a drying up of their water sources but also perhaps because of the great die-off of species over the entire world at that time.

Pterosaurs

A flying reptile, and not related to the birds and not even a dinosaur, these animals were meat eaters might have been fish eaters, scooping fish out of streams. Their long fourth finger supported the wing membrane and a wingspan of four or more feet was common. Some of the earliest pterosaurs were from the Petrified Forest area. It is likely that they were as diverse a species as the modern day birds, but since they do not fossilize well we know very little about the true extent of their species or lifestyles.

Coelophysis bauri

Remains of this small meat-eating dinosaur have been found in the Petrified Forest National Park. They were slight, quick and birdlike with keen eyesight, a long swanlike neck and may have been a herding animal. Even more of these fascinating creatures were found in New Mexico at Ghost Ranch named by local Indians for the strange sounds heard in the area. Several thousand Coelophysis from two species have been found at this site.

Chindesaurus Bryansmalli

Bone fragments rather than a complete skeleton represent this twelve-foot dinosaur. It was once thought to be the oldest dinosaur ever found but that has since been disproved. Not much is know of this fragmentary dinosaur.

The Jurassic Period
(208 million to 145 million years ago)

Rhamphinion Jenkinsi

This flying reptile is not related to birds. It had a wingspan of about 3 feet. Only fragments of teeth, a skull and a wing metacarpal have been found. Tracks, once considered those of a flying reptile, have been found in the Four Corners area but the species that made them is still being debated.

Dilophosaurus Wetherilli

This large carnivore reached a length of twenty feet. Its teeth are suited to ripping and tearing flesh but it is not known if it was a predator or a scavenger and was likely both. Its skull has two crests on top. It was found in Cameron Arizona. This reptile was made famous in the movie “Jurassic Park,” although it is highly unlikely that it spit venom or had a frilled hood. It is unfortunate that softer tissue does not fossilize well as we have no real idea of what dinosaurs really looked like in the sense of horns, hoods, crest, and such. Seeing one in the flesh would likely confuse even the best prepared paleontologist as to species.

Scutellosaurus lawleri

An armored dinosaur that reached four to five feet in length, the scutellosaurus was a bipedal running lizard that used its tail for balance. One theory has it using all four legs when walking. It was found on Ward Terrace. The armor was likely only partially effective and running may have been a good option when attacked.

Syntarsus kayentakatae

Reaching a length of six feet, this animal was excavated in the Little Colorado River Valley. Only partial skeletons have been found and more research will be needed to determine it’s lifestyle.

Massospondylus

Found on the Navajo Reservation this animal grew to almost twenty feet in length. Only partial skeletons make this one a bit of a mystery as far as here in Arizona.

The Cretaceous Period
(145 million to 65 million years ago)

Tenontosaurus

The Empire Mountains and Whetstone Mountains of southeastern Arizona each yielded a femur bone of this animal. It is believed to have reached a length of five to 25 feet and its family is still being debated. This dinosaur was likely a favorite prey animal of the larger carnosaurs as well as when young of the raptor clans.

Sonorasaurus

This dinosaur is still being excavated in southeastern Arizona and looks to be about sixty to 75 feet in length. It resembles other Brachiosaurs but is smaller in size and there is not yet a complete skeleton to further identify the species. A reconstructed skeleton is being assembled at the Arizona Sonoran Desert Museum in Tucson.

Plesiosaurs

A marine reptile, the plesiosaurs reached anywhere from ten to forty feet in size. They were predators with four flippers and moved through the water like modern day sea lions. They used their long tail to steer them through the water. Both a long necked, small head specimen and one with a shorter neck and large head have been found on Black Mesa in Arizona. Much of Arizona was under water during this period so it is likely that many more marine reptiles will be found in the future.

Tyrannosaur

The Santa Rita Mountains, southeast of Tucson Arizona, were the site of several teeth belonging to this family of dinosaurs. A carnivore, this animal reached a length of 25 to thirty feet and was a formidable predator. It was recently classified as an Albertosaurus. This is a slightly smaller version of the T rex which existed at the same time but likely had different food sources. A good example might be both lions and leopards living on the plains of Africa at this time without to much actual competition among themselves. There is no question that the Albertosaurus in Arizona was the top of the food chain, unless his bigger brother may have happened along occasionally.

There were certainly many more dinosaurs and scads of other reptiles, large and small, here in Arizona during the Mesozoic age. It is estimated that only between 10 and 15% of all dinosaur species have been uncovered. Every year new and exciting discoveries are made all over the world and even here near Tucson where the Sonorasaurus was discovered by a hiker out for a walk.

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