An article published in the “Journal of Paleontology” describes a research on the theropod dinosaurs whose fossils date back to the Late Cretaceous and were found at the site of Ellisdale, in New Jersey, USA. Chase Brownstein of the Stamford Museum and Nature Center studied fossils belonging to various families: adrosauroids (Hadrosauroidea), tyrannosaurids (Tyrannosauridae), dromaeosaurids (Dromaeosauridae) and ornithomimosaurs (Ornithomimosauria). The Ellisdale site is sometimes overlooked but these findings can provide information on the diversification of theropods throughout North America.
The Ellisdale site was discovered in 1980 and the first fossils found brought it to the attention of paleontologists. Over the subsequent years on the site fossils were found of animals of very diverse animals, from dinosaurs to crocodiles, from turtles to fish. On the east coast of North America only scattered bones and at best incomplete skeletons are generally found, the fossils found at Ellisdale have the advantage of fully representing the terrestrial animals that lived in that area. Despite that, there were delays in the study of the dinosaurs discovered.
These fossils date back to about 75 million years ago, during the Campanian, one of those that in jargon are defined ages, subdivisions of the Cretaceous period. From 2014 Chase Brownstein has been cataloging and studying them with the result of showing the diversity of the theropod dinosaurs that lived at the time not only in that site but throughout the Atlantic Coastal Plain (ACP), the region that from New Jersey goes along the Atlantic coasts to Mexico.
The image (Courtesy Chase D. Brownstein) shows the foot bone of a tyrannosaurus (A), the tooth of a giant dromaeosaurid (B), tyrannosaurus teeth (C), the limb bone of a theropod (D), a fragment of a small dromaeosaurid tooth (E) and the foot bone of an ornithomimosaurus of the group nicknamed ostrich dinosaurs (F). These are examples of the variety but also of the fragmentary nature of the fossils found in the Ellisdale site and sometimes this makes their identification difficult.
Tyrannosaurus fossils, relatives of the famous T.rex, suggest that there were two species of these large carnivores in that ecosystem. Other teeth discovered in the past and attributed to species of the same family actually belong to large-sized dromaeosaurids, the family of the dinosaurs commonly called raptors. Other teeth belong instead to smaller species of raptors.
Chase Brownstein explained that these teeth and bones are isolated and fragmented pieces and yet they can give a big hand to understand aspects of the biology of dinosaurs such as their global diversity, distribution and evolution. As an example Brownstein mentioned the fact that the fossils discovered at Ellisdale are the only ones in the Northeast of America that show an overlap in age with sites from both the south-east of the USA and in the west of North America. This makes it possible to better compare dinosaur populations throughout the continent.
In essence, the problem is that in the Ellisdale and other similar sites on the east coast of North America the fossils discovered are fragmentary so there are paleontologists who prefer to study the ones found at other sites where the skeletons were preserved with a greater completeness. Studying isolated bones or even fragments can be much more difficult and some of the ones found in Ellisdale have yet to be identified but that’s still an important job. In an area where there’s a poor fossil conservation, any fragment is useful to understand the history of the animals that lived there, in this case the theropod dinosaurs in the Late Cretaceous.