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Re: Pachycepholosaurs



>I've never accepted the intraspecific head butting hypotheses for pachy's.
>Intraspecific head butting (based on what we know from extant animals) is a
>territorial or display function.  "Cannon balls" are designed to kill; a
>result which such displays (for a number of reasons) tend to avoid.  The
>skulls of rams and other known intraspecific head butters, for example, are
>flattened in the area of impact. This has the effect of spreading the force
>of the impact over a larger area and allowing the participants to make a
lot
>of noise and appear heroic, but still walk away unharmed from the event.


    Yes, the fact that bighorns have a wider area of impact then in
pachycephalosaurs has been noted by others, though they were more concerned
with the difficulty of getting a perfect head-on impact between two "cannon
balls".   Flat headed pachycephalosaurs might have been more liekly to head
butt.
    Also, "cannon balls are designed to kill" only if they are impacting
hard enough to kill; otherwise they might just smart like crazy or crack
bones.  I wouldn't just assume that pachycephalosaurs were picking up the
speed of a cannon ball before ramming thier opponent; the "door crushing"
Pachycephalosaurus in Lost World notwithstanding.  I'd like to see a model
playing around with plausible impact speeds and the hardness of the domes
and ribcages of pachycephalosaurs before we start assuming that
pachycephalosaur impacts were frequently fatal.  Their ribcages were
extremely broad, and this has been offered as a possible way of protecting
the internal organs from impacts.
    If "cannon balls are designed to kill", then the same is certainly true
of theropod jaws, and we know that tyrannosaurs used thier teeth on each
other.  Also,  living carnivores like crocodilians and big cats, are
perfectly willing to use thier teeth and claws on members of thier own
species, with fatalities often resulting.
Intraspecific combat can be very dangerous, and accidental deaths do occur.

LNJ
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Jeffrey W. Martz
Graduate student, Department of Geosciences, Texas Tech University
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