Geoscience Reference
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turn against one another and, like their ceratopsian cousins, hit each other, whether
for mates, establishing territory, or both?
The consensus is that pachycephalosaurs' thick skulls were most likely used
for violent confrontations with one another. But figuring out why or how they used
their heads is worth lots of discussion. Fortunately, explanations for their skulls can
bereduced tojusttwo.Oneisthat pachycephalosaurs werehead-bangers, knocking
into each other directly with skull-to-skull contact. The other is that pachycephalo-
saurs went for softer targets, such as torsos, because breaking ribs might have been
less risky for an attacking pachycephalosaur than taking on a skull like its own.
Let's think ichnologically, then, about what trace fossil evidence would be
needed to figure out which of the two scenarios actually happened. Ideally, two
pachycephalosaurtrackwaysmadeatthesametimewoulddothetrick.Forhead-to-
head combat, each trackway would have long stride lengths (running at high speed)
and along the same line, but directly opposed (pachycephalosaurs ran toward each
other), and abruptly ending, with one or perhaps both trackways connecting with
much shorter and irregular steps off to the side of the previous trackways (stag-
gering away dizzily). For flank-butting combat, the trackways would be nearly the
same except one of them might be at right angles to the other, ending where they
intersect. However, as mentioned before, not one pachycephalosaur track has been
identified, let alone a trackway, let alone two trackways, let alone two intersecting
trackways made at the same time. So as much as this ichnologist hates to admit it,
we must rely on bones to resolve this problem.
In 2011, two paleontologists, Eric Snively and Jessica Theodor, had head-but-
ting in mind when they looked at skulls of
Stegoceras
and
Prenocephale
, both Late
Cretaceous pachycephalosaurs from North America. Using a combination of CT
(computer tomography) scans and computer modeling of stresses and strains that
would have been transmitted to the head and neck by this behavior, they tested
whether the additive impacts of two pachycephalosaurs were feasible or not. After
all, any such behavior, if performed regularly, might have resulted in permanent
