New Jersey Fossils Shed Light on Theropod Dinosaurs of Eastern United States

Friday, August 31, 2018

North American dinosaurs. Image credit: Davide Bonadonna.

On the east coast of North America, dinosaur fossils are rare finds. Owing to several factors, such as the mass-urbanization of the eastern seaboard, fossils from these incredible creatures are few and far between. Even the most complete skeletons are incomplete, making nearly any stray chunk of bone from the area of scientific interest.

Discovered in the early 80s, the Ellisdale fossil site of New Jersey has become well-known for preserving an unusually complete record of terrestrial animals from the eastern coast of North America from 75 million years ago, when the continent was divided as two landmasses by a large interior sea. Yet, the dinosaur fossils of the site have never been formally described.

Since 2014, researcher Chase Brownstein of the Stamford Museum and Nature Center has been tracking down elusive eastern North American dinosaurs.

Recently, Brownstein has been working on describing the ample assemblage of bones from one group of dinosaurs, the theropods, from Ellisdale.

This group of dinosaurs, which includes giant carnivores like Tyrannosaurus, smaller predators like Velociraptor, herbivorous species like the long-necked, massive claw-bearing Therizinosaurus, is the lineage to which birds belong.

Ellisdale fossils: (A) foot bone of a tyrannosaur; (B) giant dromaeosaurid (raptor dinosaur) teeth; (C), tyrannosaur teeth; (D) limb bone of a theropod dinosaur; (E) partial tooth of a small dromaeosaurid (raptor dinosaur); (F) foot bone of an ornithomimosaur (ostrich dinosaur). Image credit: Chase D. Brownstein.

At Ellisdale, the diversity of this dinosaur group is evinced by the fossils. After viewing the theropod bones and teeth from Ellisdale stored at the New Jersey State Museum, Brownstein concluded that perhaps four different species are represented at the site, one of the most diverse faunas of these dinosaurs known from east of the Mississippi River.

Tyrannosaurs distantly related to T. rex are known from teeth and a single foot bone. The teeth recovered may indicate the presence of two types of these large carnivores in the ecosystem.

Another type of dinosaur that resembled an ostrich known as an ornithomimosaur is represented by a single foot bone.

One particularly interesting finding is that several teeth previously recognized as those of tyrannosaurs are in fact those of giant dromaeosaurid, or ‘raptor,’ dinosaurs potentially more than 13 feet (4 m) long.

Some of these teeth, although incomplete, are as large or larger than teeth from other giant raptor dinosaurs already known from western North America.

Finally, some teeth from smaller raptor dinosaurs are also known from Ellisdale. As small dinosaurs are very poorly known from eastern North America, these fossils are an important addition to the record of smaller dinosaur bones.

“These bones and teeth may not be more than a few isolated, fragmentary pieces,” said Brownstein, “but they can greatly help us in better grasping aspects of dinosaur biology like their global diversity, distribution, and evolution.”

“For one, the Ellisdale assemblage of theropod dinosaurs is the only one known from the northeast that overlaps in age with sites from both the southeastern U.S. and western North America, allowing us to better compare dinosaur faunas from across the entire continent.”

“Sites like Ellisdale, although they do not produce anything along the lines of the complete skeletons known from Asia and western North America, should not be overlooked. They are a great asset to the study of paleontology because of their ability to produce fossils at all in fossil-poor regions, allowing for glimpses at the places whose deep past has been so greatly obscured.”

The research was published in the Journal of Paleontology.

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Chase D. Brownstein. The distinctive theropod assemblage of the Ellisdale site of New Jersey and its implications for North American dinosaur ecology and evolution during the Cretaceous. Journal of Paleontology, published online August 20, 2018; doi: 10.1017/jpa.2018.42

Source: www.sci-news.com

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