Chase Doran Brownstein from the Department of Ecology and Evolutionary Biology at Yale University and the Stamford Museum and Nature Center has described two new dinosaurs — a herbivorous hadrosaur and a carnivorous tyrannosaur — that lived in the North American paleolandmass Appalachia during the Late Cretaceous epoch, some 85 million years ago.
Geographic setting of the Merchantville dinosaur fauna: (a) map of North American during the Campanian stage of the Late Cretaceous epoch, showing the location of New Jersey and Delaware; (b) map of New Jersey and Delaware showing the locations from which the described specimens were recovered; (c) diagram showing preserved bones (in white) and relative sizes of (from left to right) the tyrannosaur and the hadrosaurid (adult, juvenile). Image credit: Chase Doran Brownstein, doi: 10.1098/rsos.210127.
For most of the second half of the Cretaceous period, North America was divided into two land masses, Laramidia in the West and Appalachia in the East, with the Western Interior Seaway separating them.
While famous dinosaur species like Tyrannosaurus rex and Triceratops lived throughout Laramidia, much less is known about the animals that inhabited Appalachia.
“One reason is that Laramidia’s geographic conditions were more conducive to the formation of sediment-rich fossil beds than Appalachia’s,” said Brownstein, author of a paper published in the journal Royal Society Open Science.
The specimens he examined were collected in the 1970s from the Late Cretaceous Merchantville Formation in New Jersey and Delaware.
“These specimens illuminate certain mysteries in the fossil record of eastern North America and help us better understand how geographic isolation affected the evolution of dinosaurs,” Brownstein said.
The paleontologist examined a partial skeleton of a large predatory therapod, concluding that it is probably a tyrannosaur.
He noted that the fossil shares several features in its hind limbs with Dryptosaurus, a tyrannosaur that lived about 67 million years ago in what is now New Jersey.
The dinosaur had different hands and feet than Tyrannosaurus rex, including massive claws on its forelimbs, suggesting that it represents a distinct family of the predators that evolved solely in Appalachia.
“Many people believe that all tyrannosaurs must have evolved a specific set of features to become apex predators,” Brownstein said.
“Our fossil suggests they evolved into giant predators in a variety of ways as it lacks key foot or hand features that one would associate with western North American or Asian tyrannosaurs.”
“The partial skeleton of the hadrosaur provided important new information on the evolution of the shoulder girdle in that group of dinosaurs,” he added.
“The hadrosaur fossils also provide one of the best records of this group from east of the Mississippi and include some of the only infant/perinate dinosaur fossils found in this region.”