Geoscience Reference
In-Depth Information
One of the early students of these dinosaur tracks was Roland T.
Bird, a preparator and collector at the American Museum of Natural
History. Additionally, Bird was one of the original "bikers." Through-
out the 1930s and 1940s, Bird thundered across the American West on
his Harley-Davidson motorcycle in search of dinosaur footprints.
Bird discovered numerous sites of dinosaur footprints throughout
the Southwest, and in 1937 while riding across New Mexico and Ari-
zona, he received a tip that gigantic fossil footprints had been found
along the Paluxy River in central Texas. Upon arriving in the town of
Glen Rose, he learned that the local inhabitants were well aware of the
fossils. Eventually, Bird discovered the trackway of a large theropod
dinosaur leading into the Paluxy River. With the help of a local work
crew, he diverted the water and exposed the riverbed. Imbedded in the
rock layer that formed the riverbed was an incredible sight. Fossil foot-
prints documented that at least twelve sauropods, probably bra-
chiosaurs, had walked in the same direction across a mudflat that
bordered the ancient Gulf of Mexico. More incredibly, they had been
followed at some later time by three large theropods. Analyses by Bird
and later workers, including the foremost modern expert on dinosaur
trackways, Martin Lockley from the University of Colorado near
Denver, have shown that the theropod tracks overlap and impinge
upon the sauropod tracks, documenting that the theropods passed
after the sauropods. The sauropod tracks also show that the animals
were walking side by side in the same direction at regularly spaced but
substantial intervals apart from one another. Bird interpreted these
trackways to mean that the theropods were stalking the sauropods and
that perhaps one of the meat-eaters had even attacked one of the
sauropods. In Lockley's analysis, however, no evidence in the theropod
tracks suggests that the meat-eaters sped up to catch the sauropods.
Nor does any evidence in the trackways suggest that the animals
turned to fight one another. In fact, it is not possible to determine the
time in between the passage of the two groups. It could have been
moments, or even hours. The theropods may have been hunting the
sauropods, but there is no evidence of an attack. Nonetheless, the evi-
dence that the Paluxy sauropods were traveling in a herd seems con-
vincing.
Bird discovered more compelling evidence of sauropod herding at
the nearby Davenport Ranch in 1941. There, he discovered an outcrop
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