YSM Issue 94.3

FOCUS
Paleontology
and Dryptosaurus. The program
incorporated the skeletal features of
the two dinosaur species to determine
evolutionary relationships.
From this computational analysis,
Brownstein discovered that the
Merchantville tyrannosauroid and
Dryptosaurus evolved from a common
ancestor and are part of the same clade.
That clade, known as Dryptosauridae,
is a distinct group of tyrannosaurs
that existed solely in Appalachia. For
over a century, paleontologists have
hypothesized the existence of a distinct
set of tyrannosauroids native to the
once-isolated eastern North America.
With Brownstein’s research, we now have
evidence supporting that hypothesis.
Though factors such as poor fossil
records still constitute obstacles to
our knowledge of the dinosaurs that
inhabited the east, Brownstein’s research
underscores the rise of anatomical
differences in the dinosaurs of eastern
and western North America. In a broader
context, such discoveries highlight the
profound interplay between geographical
isolation and the evolution of species.
Searching for History
Evolutionary biologists and
paleontologists often develop “just-so
stories,” speculative explanations for the
origins of a biological trait. The term
comes from Rudyard Kipling’s 1902 “Just
So Stories for Little Children.” The book
includes a collection of animal tales such
as “How the Rhinoceros Got His Skin,”
in which the rhinoceros developed
wrinkles after rubbing against a tree. In
the context of dinosaurs, there are many
speculative hypotheses that tyrannosaurs
evolved a specialized skull, superior
sight, or other specific traits to achieve
supremacy. The T. rex—the “King of the
Dinosaurs” that lived in western North
America—boasted hallmark features of
dinosaur superiority, such as a gigantic
skull, forceful jaw, powerful hindlimbs,
and muscular physique. Yet, whether
those features are indeed necessary for
biological success remains up for debate.
The eastern North American
Dryptosaurus, for example, differed from
the T. rex and other tyrannosaurs: it
had larger hands, extensive claws, and a
distinctive unit of foot bones. “Eastern
North American tyrannosaurs were
really big, were probably predators,
and had a different set of features than
western North American tyrannosaurs,”
Brownstein said. “This may cause us to
rethink the hypothesis that there was
only one way that tyrannosaurs got so big
and successful.” In this way, Brownstein’s
discoveries point towards the possibility
that tyrannosaurs achieved success
through the evolution of differing features.
As Brownstein emphasized, his
research raises broader questions of
evolution that demand further research
and contemplation—the prevailing one
among them being: how many paths
could there be to evolutionary success?
To find out more about eastern North
American dinosaurs, the next step would
be to discover a more complete skeleton
of these species. Currently, research is
limited to the fossils that have already
been found, which do not include the body
part that paleontologists consider to be
the most informative: the skull. However,
looking at living things today could also
shed light on the nature of extinct species.
Analyzing the characteristics of dinosaur
descendants can sometimes help us learn
more about their ancestors.
Behind the Discoveries
Brownstein—who has an impressive
research history, having published about
twenty peer-reviewed articles in journals
including Royal Society Open Science,
the Journal of Paleontology, Scientific
Reports, and the Zoological Journal of the
Linnean Society—intends to go forward
ABOUT THE AUTHORS
with other research while he waits for
more fossil discoveries. He is currently
studying fishes with Yale Professor and
Chair of Ecology and Evolutionary
Biology Thomas Near.
Brownstein said that he was fortunate
to have access to fossil collections like
those at the Peabody Museum and
described his appreciation for those who
have provided support and advice in his
research endeavors. “I have been very
fortunate to have people who gave me a
chance,” Brownstein said.
Brownstein has a genuine passion
for the field of research. “I have always
been really fascinated with nature, time,
what lived before, and how we got here,”
he said. Research simply makes him
happy. “If I want to do something that
I enjoy, I will do research, write, and
study things,” he said. Based on this
passion, Brownstein described science
in the larger context of the human desire
for exploration. “It is a human thing to
constantly explore. The urge to discover
is a motivator in science, and it’s a
beautiful thing,” he said.
Just like we push the boundaries of
our universe with space travel, we are
now pushing the boundaries of time
by uncovering our planet’s incredible
history. In Brownstein’s case, we now
understand that the geographical
isolation of eastern North America over
the course of thirty million years likely
provided the means for the evolution of
distinct dinosaur species.
As we continue to uncover our planet’s
incredible history, what will we discover
next? ■
ELISA HOWARD AND ANAVI UPPAL
ELISA HOWARD is a sophomore neuroscience major in Berkeley College. In addition to writing for YSM,
she volunteers at CT Hospice and Yale Community Kitchen, constructs 3D-printed limb devices through
Yale e-ENABLE, and helps organize blood drives for the American Red Cross at Yale. During the summer,
she researches neural repair in the Strittmatter Lab at the Yale School of Medicine.
ANAVI UPPAL is a sophomore astrophysics major in Pierson College. In addition to writing for YSM, she
is one of Synapse’s outreach coordinators, and she teaches science to elementary schoolers through Yale
Demos. She’s also a fall social media intern at NASA Ames Research Center.
THE AUTHORS WOULD LIKE TO THANK Chase Brownstein for his time and enthusiasm about his
research.
FURTHER READING
Doran Brownstein, C. (2021). Dinosaurs from the Santonian–Campanian Atlantic coastline substantiate
phylogenetic signatures of vicariance in Cretaceous North America. Royal Society Open Science, 8(8),
210127. https://doi.org/10.1098/rsos.210127
Marsh, O. C. (1896). The Dinosaurs of North America. Govt. Print. Off.
18 Yale Scientific Magazine October 2021 www.yalescientific.org