The Dinosaurs and Prehistoric Animals of Arizona

Woolly Mammoths and Woolly Rhinos in a Prehistoric Landscape

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Like many regions in the American West, Arizona has a deep and rich fossil history stretching back to before the Cambrian period. However, this state 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.

01
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Dilophosaurus

Dilophosaurus

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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

Sarahsaurus

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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

Sonorasaurus

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The remains of Sonorasaurus date to the middle Cretaceous period. (about 100 million years ago)

This was a relatively sparse period 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 a geology student in 1995 discovered it.

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Chindesaurus

Chindesaurus

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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

Segisaurus

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In many ways, Segisaurus was a ringer for Chindesaurus (see the previous slide), with one crucial exception: this theropod dinosaur lived during the early Jurassic period, about 183 million years ago, or approximately 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

A Carnivorous Sabre-Tooth Tiger Attacking a Young Deinotherium

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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!)