The Dinosaurs and Prehistoric Animals of Arizona

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Which Dinosaurs and Prehistoric Animals Lived in Arizona?

Alain Beneteau

Like many regions in the American west, Arizona has a deep and rich fossil history stretching all the way back to before the Cambrian period. However, this state really came into its own during the Triassic period, 250 to 200 million years ago, hosting a wide variety of early dinosaurs (as well as some later genera from the Jurassic and Cretaceous periods, and the usual assortment of Pleistocene megafauna mammals). On the following pages, you'll discover a list of the most notable dinosaurs and prehistoric animals that lived in the Grand Canyon State. (See a list of dinosaurs and prehistoric animals discovered in each U.S. state.)

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Dilophosaurus, a dinosaur of Arizona. Wikimedia Commons

By far the most famous dinosaur ever to be discovered in Arizona (in the Kayenta Formation in 1942), Dilophosaurus was so misrepresented by the first Jurassic Park movie that many people still believe that it was the size of a Golden Retriever (nope) and that it spat poison and had an expandable, fluttering neck frill (double nope). The early Jurassic Dilophosaurus did, however, possess two prominent head crests, after which this meat-eating dinosaur was named.

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Sarahsaurus,a dinosaur of Arizona. Wikimedia Commons

Named after the Arizona philanthropist Sarah Butler, Sarahsaurus had unusually strong, muscular hands capped by prominent claws, an odd adaptation for a plant-eating prosauropod of the early Jurassic period. One theory holds that Sarahsaurus was actually omnivorous, and supplemented its vegetable diet with occasional helpings of meat. (Think Sarahsaurus is a striking name? Check out a slideshow of dinosaurs and prehistoric animals named after women.)

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Sonorasaurus, a dinosaur of Arizona. Wikimedia Commons

The remains of Sonorasaurus date to the middle Cretaceous period (about 100 million years ago), a relatively sparse stretch of time for sauropod dinosaurs. (In fact, Sonorasaurus was closely related to the much better-known Brachiosaurus, which went extinct 50 million years earlier.) As you may have guessed, Sonorasaurus' euphonious name derives from Arizona's Sonora Desert, where it was discovered by a geology student in 1995.

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Chindesaurus, a dinosaur of Arizona. Wikimedia Commons

One of the most important, and also one of the most obscure, dinosaurs ever to be discovered in Arizona, Chindesaurus was only recently derived from the first true dinosaurs of South America (which evolved during the middle to late Triassic period). Unfortunately, the relatively rare Chindesaurus has long since been eclipsed by the much more common Coelophysis, the fossils of which have been unearthed by the thousands in the neighboring state of New Mexico.

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Segisaurus, a dinosaur of Arizona. Nobu Tamura

In many ways, Segisaurus was a ringer for Chindesaurus (see previous slide), with one important exception: this theropod dinosaur lived during the early Jurassic period, about 183 million years ago, or about 30 million years after the late Triassic Chindesaurus. Like most Arizona dinosaurs of this time, Segisaurus was modestly proportioned (only about three feet long and 10 pounds), and it probably subsisted on insects rather than its fellow reptiles.

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Various Megafauna Mammals

The American Mastodon, a prehistoric animal of Arizona. Wikimedia Commons

During the Pleistocene epoch, from about two million to 10,000 years ago, virtually any part of North America that wasn't underwater was populated by a wide assortment of megafauna mammals. Arizona was no exception, yielding numerous fossils of prehistoric camels, giant sloths, and even American Mastodons. (You may wonder how Mastodons could have tolerated the desert climate, but not to fret--some regions of Arizona were a bit cooler then than they are today!)