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North American Dinosaurs: What Do Fossils Say About Massive Ostrich-Like Dinosaurs?

The incredible fossil finds of two species of ornithomimosaur detail the diversity of North American dinosaurs in Appalachia.

By Sam Walters
Oct 21, 2022 7:20 PMJul 27, 2023 1:11 PM
Deinocheirus, genus of large ornithomimosaur
The Deinocheirus depicted here has sparse feathering, likely on account of its gargantuan size. (Credit: Mark Witton/Creative Commons)


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The North America of the Cretaceous Period approximately 100 to 66 million years ago was a far cry from the North America of today. Not only was the continent split into two separate landmasses, Laramidia in the west and Appalachia in the east; it was also dominated by a variety of dinosaur species, some of which bared a striking resemblance to the modern ostrich.

According to a paper published in PLOS ONE, the analysis of fossils from an ancient formation of rock in northern Mississippi has now revealed two new species of these ostrich-like dinosaurs, one of which was among the largest in the world. The analysis has also advanced scientists' understandings of dinosaur diversity in the Appalachian section of Cretaceous North America.

Appalachian Dinosaurs in North America

Ornithomimosaur that lived during the Late Cretaceous (YuRi Photolife/Shutterstock)

The fossil record of the Cretaceous landmass of Laramidia features an abundance of dinosaur specimens and a diversity of dinosaur species. But fossils from Appalachia are relatively rare in comparison, meaning that the degree of dinosaur diversity in this landmass has remained mysterious.

To uncover this mystery, researchers investigated a handful of 85-million-year-old fossils from northern Mississippi and identified two new species of ornithomimosaur. Looking like all other previously described "bird-mimic" dinosaurs, these two new species had ostrich-shaped torsos, small heads, and powerful, long legs.

Taken from one medium-sized and one large-sized ornithomimosaur, these fossils provide new insights into the amount and variety of dinosaurs in Appalachia's enigmatic past.

"The co-existence of medium- and large-bodied ornithomimosaur taxa during the Late Cretaceous," the study authors say, according to a press release, "does not only provide key information on the diversity and distribution of North American ornithomimosaurs from the Appalachian landmass, but it also suggests broader evidence of multiple cohabiting species of ornithomimosaurian dinosaurs in Late Cretaceous ecosystems."

Read More: Did All Dinosaurs Have Feathers?

Different Ornithomimosaurs Species

The Deinocheirus depicted here has sparse feathering, likely on account of its gargantuan size. (Credit: Mark Witton/Creative Commons)

Found in the Mississippian region of the Eutaw rock formation, the fossils’ proportions and patterns of growth helped the authors conclude that the fossils came from two different-sized ornithomimosaur species.

The larger of the two species probably weighed around 1,700 pounds, though the particular specimens assessed by the authors were from a juvenile individual that was likely still in the process of growing. This undoubtedly makes the larger of the two species one of the most massive ornithomimosaurs to ever exist.

According to the authors, several species of ornithomimosaur roamed the Appalachian landmass at once and some of these species reached massive sizes. Which means, these facts are part and parcel of two general patterns identified among other dinosaur groups from North America and Asia. That said, future research can only explain the reason why these two patterns were so widespread across the two continents.

Read More: The Time of Giants: How Did Dinosaurs Get So Big?

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