The Dinosaurs and Prehistoric Animals of Arkansas

of 06

Which Dinosaurs and Prehistoric Animals Lived in Arkansas?

Apatosaurus, a dinosaur of Arkansas. Flickr

For much of the last 500 million years, Arkansas alternated between extended dry spells and extended wet (meaning completely underwater) spells; unfortunately, most of the fossils discovered in this state, of small invertebrates, date from these submerged periods. Making matters worse, during the Mesozoic Era the geologic conditions in this portion of North America were unconducive to fossil formation, so we have very little evidence for dinosaurs. But don't despair: prehistoric Arkansas wasn't entirely devoid of prehistoric life, as you can learn by perusing the following slides. (See a list of dinosaurs and prehistoric animals discovered in each U.S. state.)


of 06


Ornithomimus, to which Arkansaurus was closely related. Julio Lacerda

The only dinosaur ever to be discovered in Arkansas, Arkansaurus was initially classified as a specimen of Ornithomimus, the classic "bird mimic" dinosaur that resembled an ostrich. The problem is that the sediments where Arkansaurus was unearthed (in 1972) predate the golden age of Ornithomimus by several million years; another possibility is that this dinosaur represents an entirely new genus of ornithomimid, or perhaps a species of the equally obscure Nedcolbertia.

of 06

Various Sauropod Footprints

sauropod footprint
A sauropod footprint.

The Nashville Sauropod Trackway, in a gypsum mine near Nashville, Arkansas, has yielded literally thousands of dinosaur footprints, most of them belonging to sauropods (the huge, four-footed plant eaters of the late Jurassic period, typified by Diplodocus and Apatosaurus). Clearly, herds of sauropods traversed this region of Arkansas during their periodic migrations, leaving footprints (possibly separated by millions of years of geologic time) up to two feet in diameter!

of 06


giant ground sloth
The Giant Ground Sloth, a prehistoric mammal of Arkansas. Wikimedia Commons

Just as Arkansaurus (see slide #2) is the most complete dinosaur ever to be discovered in Arkansas, so Megalonyx, also known as the Giant Ground Sloth, is the most complete prehistoric mammal. The claim to fame of this 500-pound beast of the late Pleistocene epoch is that its type fossil (discovered in West Virginia rather than Arkansas) was originally described by Thomas Jefferson, years before he became the third president of the United States.

of 06


The fossil of Ozarcus. American Museum of Natural History

Named after the Ozark Mountains, Ozarcus was a three-foot-long prehistoric shark of the middle Carboniferous period, about 325 million years ago. When it was announced to the world, in April 2015, Ozarcus was one of the most complete ancestral sharks ever identified in North America (cartilage doesn't preserve well in the fossil record, so most sharks are represented by their scattered teeth). What's more, Ozarcus appears to have been an important "missing link," adumbrating the evolution of sharks during the later Mesozoic and Cenozoic eras.

of 06

Mammoths and Mastodons

woolly mammoth
A herd of Woolly Mammoths. Heinrich Harder

Although Megalonyx (see slide #4) is Arkansas' best-known prehistoric mammal, this state was home to all kinds of gigantic fauna during the late Pleistocene epoch, about 50,000 years ago. No intact, headline-generating specimens have been discovered, but researchers have unearthed the scattered remains of Woolly Mammoths and American Mastodons, which were thick on the ground all across North America until they perished shortly after the last Ice Age.