Geoscience Reference
In-Depth Information
The most recently discovered dinosaur-resting trace, and probably the best, is
a spectacular one. Reported in 2009 in southwestern Utah, this Early Jurassic trace
fossil not only shows where a theropod approached a sitting spot and sat down, but
also got up and walked a ways afterwards. Just like how we would adjust our sit-
ting position to a more comfortable one, this dinosaur shuffled forward twice after
lowering itself to the ground, evidenced by repeated prints of the same feet. It also
includes impressions of its metatarsals, ischial callosity, and two thin slices left by
its tail.
An even more remarkable aspect of this sitting trace, though, is that the thero-
pod put its hands down in front of it and left impressions of these. The traces
showedthepositionsofthetheropod'shandswithits“palms”turnedinwardtoward
the center of the body, almost as if it were measuring the width of the trackway.
For too many years, paleontologists have cringed at reconstructions of theropods
walking around limp-wristed, palms down: a posture sometimes derisively labeled
as “bunny hands.” In fact, skeletal evidence indicates this was anatomically im-
possible, and that the hands must have been held with the palms turned inward,
not downward. Thus these two handprints vindicated critics' previous assertions of
theropodhandpositions.Thiscombinedrestingtraceandtrackway,alongwithhun-
dredsofotherdinosaurtracks,warrantedenoughimportancetohaveabuildingcon-
structed around them for protection (the St. George Dinosaur Discovery Center),
ably providing public education about the tracks in St. George, Utah.
Nevertheless, as wonderful as this trace fossil might be, my favorite dinosaur-
resting trace is one made by an Early Jurassic theropod in what we now call Mas-
sachusetts. On display at the Beneski Museum of Natural History at Amherst Col-
lege, this specimen, designated specimen AC 1/7 by paleontologist Edward Hitch-
cock in the 1850s, is a near-perfect record of where a human-sized theropod sat
down on a muddy lakeshore just a little less than 200 million years ago. Unlike the
St. George example, this trace fossil is quite limited in its area, preserved in an isol-
ated slab of rock about the size of a coffee table. At some point after its discovery
