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Re: Ceratopian jaws (my last bow)
Jon Woolf writes;
>I don't understand why anyone would think that the ceratopsid frill
>served to anchor jaw muscles at all. I recently read Peter Dodson's
>book THE HORNED DINOSAURS, in which he makes a convincing (to me, at
>least) case that the frill's primary function was display, possibly
>with a secondary protective function. Put together, these two reasons
>seem to more than adequately explain the frill. I don't see any need
>for the "jaw muscles" idea, and I don't see any good reason to accept
>it. I do see a lot of questions that it raises, though. For example:
The idea stems from observations of the evolution of the group. The first
ceratopian (note the missing "s"), 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. In the
protoceratopids, the fenestra pair seem to be a match with the openings on
the first simple frill. Therefore, one could conclude that the frill first
originated as a way to help the jaw muscles somehow (perhaps as a better
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.
> * No other type of dinosaur had enormous jaw muscles, not even
> the ceratopsids' own ancestors.
_Protoceratops_ has a well developed frill, and most likely needed it to go
after the available vegetation. I understand that desert plantlife is not
exactly chewer friendly.
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. This idea would allow several groups of
herbivores to live in the same area, with little interspecies competition
(the definition of ecological stratification). However, I have no idea if
the paleobotany backs up this statement.
> * Different ceratopsid genera had different frill sizes and
> shapes, and also different sizes, shapes, and placements of the
> frill openings. Why such a variety of forms to answer a single
> common requirement (jaw muscle anchorage)?
The idea of ecological stratification could explain this: different
species/genera going after differing vegetation, with differing degrees of
Since this is the last week in the semester, and will be un-subscribing
soon, I must cut out of the discussion. Next semester, I will be back at
my old college to pick up a few classes I missed my first time around, so
my address will be back to what it was last year.
Later all, [poof!]
Orphan Vertebrate Paleontologist
"Happy Christmas to all, and to all a good night!"