The Dinosaurs and Prehistoric Animals of Idaho

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Which Dinosaurs and Prehistoric Animals Lived in Idaho?

hagerman's horse
Hagerman's Horse, a prehistoric mammal of Idaho. Wikimedia Commons

You might think, given its proximity to dinosaur-rich states like Utah and Wyoming, that Idaho would be teeming with the fossils of raptors and tyrannosaurs. The fact is, though, that this state was underwater during much of the Paleozoic and Mesozoic eras, and it was only during the later Cenozoic that its geologic sediments lent themselves to the preservation of megafauna mammals. On the following slides, you'll learn about the most notable dinosaurs and prehistoric animals ever to be discovered in the Gem State. (See a list of dinosaurs and prehistoric animals discovered in each U.S. state.)

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Tenontosaurus, a dinosaur of Idaho. Alain Beneteau

The Tenontosaurus fossils discovered in Idaho can be considered a spillover from neighboring Wyoming, where this middle Cretaceous ornithopod roamed in vast herds. The two-ton Tenontosaurus is famous for having been on the lunch menu of Deinonychus, a feathered raptor that likely hunted in packs to bring this bigger plant-eater down. (Deinonychus, of course, may also have roamed Cretaceous Idaho, but paleontologists have yet to adduce any direct fossil evidence.) Of course, you can be sure that if Tenontosaurus lived in prehistoric Idaho, other ornithopods and hadrosaurs made this state their home; the trouble is that their fossils have yet to be discovered.

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Oryctodromeus, a dinosaur of Idaho. Joao Boto

In 2014, a middle Cretaceous fossil bed discovered in southeastern Idaho yielded the remains of Oryctodromeus, a small (only about six feet long and 100 pound) ornithopod that burrowed beneath the soil to escape the notice of larger predators. How do we know that Oryctodromeus pursued this not-very-common lifestyle? Well, this dinosaur's tail was unusually flexible, which would have allowed it to curl up into a ball, and its unusually pointy snout was the ideal shape for digging. It may even be possible that Oryctodromeus (and other ornithopods like it) was covered with feathers, which would upend our understanding about dinosaur metabolism.

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The Hagerman Horse

american zebra
Hagerman's Horse, a prehistoric mammal of Idaho. Wikimedia Commons

Also known as the American Zebra and Equus simplicidens, the Hagerman Horse was one of the earliest species of Equus, the umbrella genus that comprises modern horses, zebras and donkeys. This Pliocene horse ancestor may or may not have sported zebra-like stripes, and if so, they were probably restricted to limited portions of its body, such as its rump and legs. The American Zebra is represented in the fossil record by no less than five complete skeletons and a hundred skulls, all discovered in Idaho, the remains of a herd that drowned in a flash flood about three million years ago.

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Mammoths and Mastodons

The American Mastodon, a prehistoric mammal of Idaho. Wikimedia Commons

During the Pleistocene epoch, from about two million to 10,000 years ago, the state of Idaho was pretty much as high and dry as it is today--and like pretty much every other region of North America, it was traversed by all sorts of megafauna mammals, including Columbian and Imperial (but not Woolly) Mammoths and American Mastodons. This state was also home to Saber-Toothed Tigers and Giant Short-Faced Bears, although the fossil evidence for these mammals is much more fragmentary. Suffice it to say that if you hopped into a time machine and journeyed back to the Pleistocene, you may want to equip yourself with suitable clothing.

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Your Citation
Strauss, Bob. "The Dinosaurs and Prehistoric Animals of Idaho." ThoughtCo, Aug. 25, 2020, Strauss, Bob. (2020, August 25). The Dinosaurs and Prehistoric Animals of Idaho. Retrieved from Strauss, Bob. "The Dinosaurs and Prehistoric Animals of Idaho." ThoughtCo. (accessed June 8, 2023).