Some species of ornithomimosaurs that lived in what is now Mississippi, the United States, some 85 million years ago were among the world’s largest at over 800 kg, according to new research.
“During the majority of the Late Cretaceous, the southern North American continent was divided into two landmasses by the expansion of the Western Interior Seaway, forming Laramidia to the west and Appalachia to the east,” said Dr. Chinzorig Tsogtbaatar from the North Carolina Museum of Natural Sciences and colleagues.
“The continental separation had appreciable consequences for the evolution of North American dinosaurs, with distinct lineages evolving in isolation on each landmass.”
“Although the vertebrate fossil record of Appalachia suggests a distinct and diverse fauna, the majority of this record is based on relatively poorly preserved, and often isolated specimens, when compared to the more extensive record of Laramidian species.”
“This is due, in part, to preservational and collection biases, as the vast majority of the exposed sedimentary units in Appalachia represent marine deposits and preserved fossils of terrestrial species are often fragmentary.”
“Thus, Appalachia’s dinosaur fossil record is poor compared to the extensive record of terrestrial and coastal plain deposits in Laramidia.”
In the new study, the researchers examined multiple specimens of ornithomimosaur dinosaurs from the Santonian Eutaw Formation of Mississippi.
“Ornithomimosaurs, the so-called bird-mimic dinosaurs, were superficially ostrich-shaped with small heads, long arms, and strong legs,” they explained.
“The new fossils, including foot bones, are around 85 million years old, making them a rare glimpse into a poorly known interval of North American dinosaur evolution.”
By comparing the proportions of these fossils and the patterns of growth within the bones, the paleontologists determined that the fossils likely represent two different species of ornithomimosaurs, one relatively small and one very large.
They estimate the larger species to have weighed over 800 kg, and the individual examined was likely still growing when it died. This makes it among the largest ornithomimosaurs known.
The fossils provide valuable insights into the otherwise poorly understood dinosaur ecosystems of Late Cretaceous eastern North America.
They also shed light on ornithomimosaur evolution; giant body sizes and multiple species living side-by-side are recurring trends for these dinosaurs across North America and Asia.
“The ornithomimosaur materials from the Eutaw Formation provide key information on the diversity and distribution of North American ornithomimosaurs and Appalachian dinosaurs and fit with broader evidence of multiple cohabiting species of ornithomimosaurian dinosaurs in Late Cretaceous ecosystems of Laurasia,” the researchers concluded.
Their findings will be published in the journal PLoS ONE.
C. Tsogtbaatar et al. 2022. Large-bodied ornithomimosaurs inhabited Appalachia during the Late Cretaceous of North America. PLoS ONE 17 (10)
Source link: https://www.sci.news/paleontology/eutaw-formation-ornithomimosaurs-11309.html