Geoscience Reference
In-Depth Information
Sowhydidthesetracefossilsgetreversedinimportancebythepaleontologists
who studied them? Probably because dinosaur skin impressions are rare, evidence
of wounded skin is rarer, and evidence of healed skin is exceptional. Hence it was
the skin that justifiably became the focus of the study, whereas the multiple tooth-
marks in the bone below it became additional information, shuffled to the back-
ground because they seemed so ordinary—which they most assuredly are not.
Old Ailments, Traces, and False Traces
The discernment of dinosaur disorders falls under the category of
paleopathology
,
which isthe studyofancient ailments. Although notall ofpaleopathology concerns
itself with dinosaurs—much of it centers on evidence for diseases in pre-historic
human remains—this science is being applied enthusiastically to dinosaurs. In
the practice of paleopathology, physicians and veterinarians sometimes collaborate
with paleontologists in a neat mix of old and new.
Still, we must always return to basic principles of ichnology before allowing
ourselves to be dazzled by other sciences. For any paleopathologic evidence in
fossilbones,skin,orteethtoqualifyasadinosaurtracefossil,itmusthavebehavior
behind it. This criterion is necessary regardless of whether a trace fossil was made
by the dinosaur with the injury, from another dinosaur, or from a non-dinosaur an-
imal.
For example, one specimen of
Psittacosaurus
from Early Cretaceous rocks of
China also, like the
Edmontosaurus
, has a skin impression associated with its body,
andtheskinimpression hastwoapparent puncturemarks.Butthesemarksshowno
signofhealing.Accordingly,paleontologistswouldsimplysaythesetracesarefrom
predation or scavenging by another animal that intended to eat this already-dead
Psittacosaurus
. Possibly the tracemaker was a theropod, or maybe it was another
animal that also had pointed teeth, such as a lizard or crocodilian. So rather than
showing how this dinosaur escaped an attack, with its punctured skin later closing
up and leaving a noticeable scar, this was evidence that its inert body was included
on some animal's meal plan.
