Fossils illuminate dinosaur Tyrannosaurus rex evolution in eastern North America

Tyrannosaurus rex, the fearsome predator that when roamed what’s now western North America, appears to possess had an East Coast cousin. a replacement study describes two dinosaurs that inhabited Appalachia — a once isolated land mass that today composes much of the eastern us — about 85 million years ago: an herbivorous duck-billed hadrosaur and a carnivorous tyrannosaur

A new study by Yale undergraduate Chase Doran Brownstein describes two dinosaurs that inhabited Appalachia — a once isolated land mass that today composes much of the eastern us — about 85 million years ago: an herbivorous duck-billed hadrosaur and a carnivorous tyrannosaur. The findings were published Aug. 25 within the journal Royal Society Open Science.

The two dinosaurs, which Brownstein described from specimens housed at Yale’s Peabody Museum of explanation , help fill a serious gap within the North American fossil record from the Late Cretaceous and supply evidence that dinosaurs within the eastern portion of the continent evolved distinctly from their counterparts in western North America and Asia, Brownstein said.

“These specimens illuminate certain mysteries within the fossil record of eastern North America and help us better understand how geographic isolation — large water bodies separated Appalachia from other landmasses — affected the evolution of dinosaurs,” said Brownstein, who is entering his junior year at Yale College. “They’re also an honest reminder that while the western us has long been the source of exciting fossil discoveries, the eastern a part of the country contains its share of treasures.”

For most of the last half of the Cretaceous, which ended 66 million years ago, North America was divided into two land masses, Laramidia within the West and Appalachia within the East, with the Western Interior Seaway separating them. While famous dinosaur species like T. rex and Triceratops lived throughout Laramidia, much less is understood 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, Brownstein explained.

The specimens of Tyrannosaurus described within the new study were discovered largely during the 1970s at the Merchantville Formation in present day New Jersey and Delaware. They constitute one among the sole known dinosaur assemblages from the late Santonian to early Campanian stages of the Late Cretaceous in North America. This fossil record period, dating from about 85 to 72 million years ago, is restricted , Brownstein noted.

Brownstein examined a partial skeleton of an outsized predatory therapod, concluding that it’s 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’s now New Jersey. The dinosaur has different hands and feet than T. rex, including massive claws on its forelimbs, suggesting that it represents a definite family of the predators that evolved solely in Appalachia.

“Many people believe that each one tyrannosaurs must have evolved a selected set of features to become apex predators,” Brownstein said. “Our fossil suggests they evolved into giant predators during a sort of ways because it lacks key foot or hand features that one would accompany western North American or Asian tyrannosaurs.”

The partial skeleton of the Tyrannosaurus provided important new information on the evolution of the pectoral arch therein group of dinosaurs, Brownstein found. The hadrosaur fossils also provide one among the simplest records of this group from east of the Mississippi and include a number of the sole infant/perinate (very young) dinosaur fossils found during this region