The Dinosaurs and Prehistoric Animals of Wyoming

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Which Dinosaurs and Prehistoric Animals Lived in Wyoming?

Uintatherium, a prehistoric mammal of Wyoming. Nobu Tamura

As is the case with many states in the American west, the diversity of prehistoric life in Wyoming is inversely proportional to the number of human beings that live there today. Since its sediments were geologically active all through the Paleozoic, Mesozoic and Cenozoic eras, Wyoming literally teems with over 500 million years' worth of fossils, ranging from fish to dinosaurs to birds to megafauna mammals--all of which you can learn about by perusing the following slides. (See a list of dinosaurs and prehistoric animals discovered in each U.S. state.)

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Stegosaurus, a dinosaur of Wyoming. Munich Dinosaur Park

Of the three most prominent species of Stegosaurus discovered in Wyoming, two come with asterisks attached. Stegosaurus longispinus was equipped with four unusually long neural spines, a hint that it may actually have been a species of Kentrosaurus, and Stegosaurus ungulatus was probably a juvenile of a Stegosaurus species first discovered in Colorado. Luckily, the third species, Stegosaurus stenops, rests on firmer foundations, as it's represented by over 50 fossil specimens (not all of them from Wyoming).

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Deinonychus, a dinosaur of Wyoming. Wikimedia Commons

One of the many dinosaurs that Wyoming shares in common with neighboring Montana, Deinonychus was the model for the "Velociraptors" in Jurassic Park--a voracious, feathered, human-sized raptor that preyed on the plant-munching dinosaurs of the late Cretaceous period. This big-clawed theropod also inspired John Ostrom's theory that birds evolved from dinosaurs, controversial when it was first broached in the 1970's but broadly accepted today.

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Triceratops, a dinosaur of Wyoming. Wikimedia Commons

Although Triceratops is the official state dinosaur of Wyoming, the first known fossil of this horned, frilled dinosaur was actually discovered in nearby Colorado--and misinterpreted by the famous paleontologist Othniel C. Marsh as a species of bison. It was only when a near-complete skull was unearthed in Wyoming that scientists realized they were dealing with a late Cretaceous dinosaur rather than a megafauna mammal, and Triceratops was launched on the road to fame and fortune.

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Ankylosaurus, a dinosaur of Wyoming. Wikimedia Commons

Although Ankylosaurus was first discovered in neighboring Montana, a later find in Wyoming is even more intriguing. The famous fossil-hunter Barnum Brown unearthed the scattered "scutes" (armored plates) of this plant-eating dinosaur in association with some Tyrannosaurus Rex remains--a hint that Ankylosaurus was hunted (or at least scavenged) by meat-eating dinosaurs. Clearly, a hungry T. Rex would have had to flip this armored dinosaur onto its back and dig into its soft, unprotected belly.

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Various Sauropods

Camarasaurus, a dinosaur of Wyoming. Nobu Tamura

In the late 19th century, a huge number of sauropod remains were discovered in Wyoming, which figured prominently in the "Bone Wars" between the rival paleontologists Othniel C. Marsh and Edward Drinker Cope. Among the well-known genera that denuded this state of vegetation during the late Jurassic period were Diplodocus, Camarasaurus, Barosaurus, and Apatosaurus (the dinosaur formerly known as Brontosaurus).

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Various Theropods

Ornitholestes, a dinosaur of Wyoming. Royal Tyrrell Museum

Theropods--meat-eating dinosaurs, large and small--were a common sight in Mesozoic Wyoming. Fossils of the late Jurassic Allosaurus and the late Cretaceous Tyrannosaurus Rex have both been discovered in this state, which is also represented by such widely differing genera as Ornitholestes, Coelurus, Tanycolagreus and Troodon, not to mention Deinonychus (see slide #3). As a rule, when these carnivores weren't preying on each other, they targeted slow-witted hadrosaurs and the juveniles of Stegosaurus and Triceratops.

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Various Pachycephalosaurs

Stegoceras, a dinosaur of Wyoming. Sergey Krasovskiy

Pachycephalosaurs--Greek for "thick-headed lizards"--were small- to medium-sized plant-eating dinosaurs that head-butted each other with their extra-thick skulls for dominance in the herd (and, possibly, also butted away the flanks of approaching predators). Among the genera that prowled late Cretaceous Wyoming were Pachycephalosaurus, Stegoceras, and Stygimoloch, the last of which may turn out to be a "growth stage" of Pachycephalosaurus.

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Prehistoric Birds

Gastornis, a prehistoric bird of Wyoming. Wikimedia Commons

If you crossed a duck, a flamingo and a goose, you might wind up with something like Presbyornis, a prehistoric bird that has puzzled paleontologists ever since its discovery in Wyoming in the late 20th century. Currently, expert opinion tends toward Presbyornis having been a primitive duck, though that conclusion may change pending further fossil evidence. This state was also home to Gastornis, previously known as Diamytra, a dinosaur-sized bird that terrorized the wildlife of the early Eocene epoch.

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Prehistoric Bats

Icaronycteris, a prehistoric bat of Wyoming. Wikimedia Commons

During the early Eocene epoch--about 55 to 50 million years ago--the first prehistoric bats appeared on earth, the well-preserved fossils of which have been discovered in Wyoming. Icaronycteris was a tiny bat progenitor that already possessed the ability to echolocate, a quality lacking in its flying mammalian contemporary, Onychonycteris. (Why are bats important, you may ask, especially compared to the dinosaurs on this list? Well, they're the only mammals ever to have evolved powered flight!)

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Prehistoric Fish

Knightia, a prehistoric fish of Wyoming. Nobu Tamura

The official state fossil of Wyoming, Knightia was a prehistoric fish, closely related to the modern herring, that swam the shallow seas covering Wyoming during the Eocene epoch. Thousands of Knightia fossils have been discovered in Wyoming's Green River formation, along with specimens of other ancestral fish like Diplomystus and Mioplosus; some of these fossil fish are so common that you can buy your own specimen for a hundred bucks! 

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Various Megafauna Mammals

Uintatherium, a prehistoric mammal of Wyoming. Charles R. Knight

As with dinosaurs, it's impossible to list individually all the megafauna mammals that inhabited Wyoming during the Cenozoic Era. Suffice it to say that this state was well-stocked with ancestral horses, primates, elephants and camels, as well as bizarre "thunder beasts" like Uintatherium. Sadly, all of these animals went extinct either well before or right at the cusp of the modern era; even horses had to be reintroduced to North America, in historical times, by European settlers.

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Strauss, Bob. "The Dinosaurs and Prehistoric Animals of Wyoming." ThoughtCo, Feb. 16, 2021, Strauss, Bob. (2021, February 16). The Dinosaurs and Prehistoric Animals of Wyoming. Retrieved from Strauss, Bob. "The Dinosaurs and Prehistoric Animals of Wyoming." ThoughtCo. (accessed June 10, 2023).