Fossils illuminate dinosaur evolution in eastern North America

Date:
August 25, 2021
Source:
Yale University
Summary:
Tyrannosaurus rex, the fearsome predator that once roamed
what is now western North America, appears to have had an East
Coast cousin. A new study describes two dinosaurs that inhabited
Appalachia -- a once isolated land mass that today composes much
of the eastern United States -- about 85 million years ago: an
herbivorous duck-billed hadrosaur and a carnivorous tyrannosaur.



FULL STORY ========================================================================== Tyrannosaurus rex, the fearsome predator that once roamed what is now
western North America, appears to have had an East Coast cousin.


==========================================================================
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 United States -- about 85 million
years ago: an herbivorous duck-billed hadrosaur and a carnivorous
tyrannosaur. The findings were published Aug. 25 in the journal Royal
Society Open Science.

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

"These specimens illuminate certain mysteries in 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 a good
reminder that while the western United States has long been the source
of exciting fossil discoveries, the eastern part of the country contains
its share of treasures." For most of the second half of the Cretaceous,
which ended 66 million years ago, 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 T. rexand 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, Brownstein explained.

The specimens described in the new study were discovered largely during
the 1970s at the Merchantville Formation in present day New Jersey
and Delaware.

They constitute one of the only 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 limited, Brownstein noted.



========================================================================== Brownstein 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 has different hands and feet than T. 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, Brownstein found.

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
(very young) dinosaur fossils found in this region.

Brownstein, who works as a research associate at the Stamford Museum
and Nature Center in Stamford, Connecticut, has previously published his paleontological research in several peer-journals, including Scientific Reports, the Journal of Paleontology, and the Zoological Journal of
the Linnaean Society. In addition to eastern North American fossils, he currently focuses his research on the evolution of fishes, lizards, and
birds. He is particularly interested in how geographic change and other
factors contribute to how fast different types of living things evolve.

He currently works in the lab of Thomas J. Near, curator of the Peabody Museum's ichthyology collections and professor and chair of the Department
of Ecology and Evolutionary Biology at Yale. Brownstein also collaborates
with Yale paleontologists Jacques Gauthier and Bhart-Anjan Bhullar in
the Department of Earth and Planetary Sciences.

While Brownstein is considering pursuing an academic career in
evolutionary biology, he says his research is driven by enjoyment.

"Doing research and thinking about these things makes me
happy," he said. "Like biking, it's something I love to do." ========================================================================== Story Source: Materials provided by Yale_University. Original written
by Mike Cummings. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Chase Doran Brownstein. Dinosaurs from the Santonian-Campanian
Atlantic
coastline substantiate phylogenetic signatures of vicariance in
Cretaceous North America. Royal Society Open Science, 2021; 8 (8):
210127 DOI: 10.1098/rsos.210127 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210825143032.htm

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