Geoscience Reference
In-Depth Information
Pachycephalosaurs
—these dinosaurs, often nicknamed “bone-headed dino-
saurs”becauseoftheirthick,bonyskulls,shareacommonancestorwiththoseother
big-headed dinosaurs, ceratopsians. Yet we know nothing about their tracks, be-
causeweknownothingabouttheirfeet.Sofar,nopachycephalosaurfootpartshave
been discovered, meaning that we can only speculate about what their tracks look
like. Based on what we do know from their skeletal remains, we think they were
mostly bipedal, so their tracks mostly just show alternating right-left rear foot im-
pressions. Such tracks possibly might resemble those of their ceratopsian cousins,
which have four toes on the rear foot. If so, that difference would be helpful when
distinguishing their tracks from those of ornithopods or theropods.
So you might get the impression that, armed with digit numbers and know-
ledge of the basic groups of dinosaurs, identifying their tracks will be oh-so-easy, a
leisurely stroll in the park while also attended by servants providing tea, backrubs,
and answering your e-mail for you. Once you come back from your saunter down
a fantasyland version of how dinosaur ichnology is done (hey, I've been there, and
visititoften)andarereadytodoalittlemorethinking,hereiswhatelseyou'llneed
to know.
For instance, you've probably already noticed that most theropod and ornitho-
pod tracks are three-toed. Then how do we tell the difference between them, espe-
cially if they're preserved in rocks of the same age and place? This can get tricky,
especially if the tracks are poorly preserved. But the easiest way to tell the differ-
ence between a theropod track and an ornithopod track is to apply three criteria: (1)
look at the length of the foot versus its width; (2) check out the width of its toes;
and (3) see whether it has claws that end in points or if they're a little more blunt.
Theropods usually left tracks that are longer than they are wide, with thin toes and
sharp claws, whereas ornithopod tracks are typically wider than they are long, with
thicker toes and blunt tips. Again, there are exceptions to this generality, and even
dinosaur-track experts have doubts about the identity of some three-toed dinosaur
tracks, especially if a rival dinosaur-track expert identified them. But with applica-
