Geoscience Reference
In-Depth Information
nology of dinosaurs. In the late 19th century, Darwin was aware of the few Jurassic
and Cretaceous non-avian dinosaurs that had been discovered in the United King-
dom and elsewhere, as well as the Late Jurassic
Archaeopteryx
from Germany. But
he did not know, nor could he have suspected at the time, that birds are dinosaurs.
Interestingly,fossiltheropodandornithopodtrackswerealreadyknownduring
Darwin's lifetime, but their makers had been misidentified. For instance, in 1845
he corresponded with ichnologist Edward Hitchcock of Amherst College in Mas-
sachusetts, who surmised that Late Triassic and Early Jurassic dinosaur tracks from
the Connecticut River Valley were oversized bird tracks. In that letter to Hitchcock,
in which Darwin refers to these dinosaur tracks as “footsteps,” he mused about the
meaning of these tracks with relation to birds:
In my opinion these footsteps (with which subject your name is certain to
go down to long future posterity) make one of the most curious discover-
ies of the present century & highly important in its several bearings. How
sincerely I wish that you may live to discover some of the bones belonging
to these gigantic birds: how eminently interesting it would be (to) know
whether their structure branches off towards the Amphibia, as I am led to
imagine that you have sometimes suspected
.
Had both Hitchcock and Darwin lived to today, they would have been disap-
pointed tolearn that thiswistful hopeoffindingbonesofthose“gigantic birds” (di-
nosaurs, as it were) would have been largely unfulfilled. As of this writing, despite
continued discoveries of theropod and ornithopod tracks, almost no dinosaur bones
are known from the Connecticut River Valley. Furthermore, body fossils of birds
are unknown from rocks older than the Late Jurassic anywhere in the world.
Nonetheless, even though Darwin and Hitchcock missed the connection
betweendinosaurtracks,theevolutionofbirds,andbiogeography,theyeachintheir
own way linked these seemingly disparate subjects. What Hitchcock got right, but
without knowing it, was how the close resemblance of theropod tracks to those of
