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Re: Ceratopian jaws (my last bow)
From: Robert J Meyerson <firstname.lastname@example.org> (Rob Meyerson)
> The idea stems from observations of the evolution of the group. ...
> and the only bipedal member of the group, was _Psittacosaurus_.
> In this animal, the jaw muscles appear to attach to the fenestra
> pair located at the back/top of the head. ...
> An added benefit of a frill is that it is a free billboard for all
> kinds of advertisements. Not only is it helpful during a rut, but
> it also is a great species marker. However, I suggest that this
> is a secondary benefit to what frill provides to the jaw.
It could well be that the frill *originated* as jaw muscle attachment,
and then diversified and enlarged due to sexual selection of it as
Thus the large size and prominant shape variations would be due to the
display function, even though it was anatomically originally an
I would suggest that the largest a frill would get due purely to
use for muscle attachments is found in animals like _Protoceratops_,
and even there some secondary enlargement might be present in the males.
> I am of the opinion that North American ceratopians were going after
> vegetation that was considerably tougher than hadrosaur fare,
> resulting in a need for a good set of jaws.
The difficulty with this is that there is little evidence for abundant
high-fiber plant material in the Late Cretaceous of North America. In
fact the vegetation in question was dominated by varying mixtures of
sequoias, flowering trees, gingos, ferns, and "ur-sedges". Over much
of the area where _Triceratops_ is found even palms are rather rare.
> This idea would allow several groups of herbivores to live in the
> same area, with little interspecies > competition (the definition
> of ecological stratification). ...
I agree there has to have been ecological differentiation. But in
modern ecosystems terrestrial herbivore differentiation is often
One point that is of some significance is that _Edmontosaurus_
remains are mroe often associated with swamp deposits than are
_Triceratops_ remains. This alone may be sufficient ecological
differentiation for the Lancian exemplars Similar behavioral/
micro-habitat differentiation may have been involved during the
earlier times, when diversity in both groups was higher.
> However, I have no idea if the paleobotany backs up this statement.
I do not believe it does. If people wish I can post my raw data on
the plants of the Hell Creek and Lance Formations.
[I will reserve my more detailed analysis for later use].
> The idea of ecological stratification could explain this: different
> species/genera going after differing vegetation, with differing
> degrees of toughness.
The differences in shape do not, to my eye, really match with what
differences in mechanics would require. The differences are more
related to appearance (squared in _Chasmosaurus_, spikey in
_Styracosaurus_ and so on - even the forward facing spikes on
_Centrosaurus_ seem to me to be more visual than functional).
The peace of God be with you.