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Re: Triceratops Skull



Shara (sdhughes) wrote:

> I have recently attended a introductory University course on the evolution of
> Dinosaurs at the University of Alberta. The prof in this course told us that
> Paleontologists have relatively recently come up with theories about the
> Triceratops skull.

There have been many hypotheses about this.

> The theory is that the extended back ridge of the skull was
> actually used for attachment of muscles for the jaw.

This is one hypothesis.  And it is probably correct up to a point.  Robert 
Bakker
attributes the idea to John Ostrom (1963) in his (Bakker's) 1986 book, _The
Dinosaur Heresies_.  The hypothesis suggests that _Triceratops_ and similar 
horned
dinosaurs were adapted to produce great leverage and a more powerful bite by the
configuration and great mass of the jaw muscles, which extended nearly to the
trailing edge of the frill.  This hypothesis has been disputed on the basis that
the most posterior frill surfaces don't show muscle scarring.  And if I 
understand
correctly, very long muscles have a greater ability to stretch (and thus to open
the jaws wider, as in a saber tooth cat), but muscle length doesn't necessarily
provide greater power.  None the less, even with shorter jaw muscles,
_Triceratops_ is thought to have possessed formidable shearing jaws.  See 
Dodson's
_The Horned Dinosaurs_ for more discussion of this topic.  And follow up on the
footnotes and references for more.  It may well be that basal marginocephalians
(something similar to _Psittacosaurus_) originally developed a posterior shelf 
on
the skull to anchor the jaw muscles, and the neoceratopsians expanded the frill 
to
a remarkable degree for a combination of reasons.

> As well as this muscle
> they believe that there was a large muscle behind the ridge to aid in lifting
> their massive skulls. This gives the Triceratops a more bull-like appearance.
> Is this a common theory?

I don't know, but this hypothesis was proposed a long time ago, too.  See C. W.
Gilmore's diminutive model of _Torosaurus_ restored in just this way in Don 
Glut's
_The Dinosaur Dictionary_ (1972 -- page 291 in the first edition).  The book
credits this model to the Academy of Natural Sciences (Philadelphia).

The most obvious (though not necessarily the most favored) hypothetical use for
the large frill was defense (as a shield), but this certainly would probably not
explain the purpose of the frill for other ceratopsians, whose frills sported
gaping holes (fenestrae).

Display may be the most favored hypothesis today.  The frills may have 
advertised
an animal's sexual maturity, size, and power to mates, competitors, and (the
latter two conditions) to predators, especially if the frills were brightly
colored.

Thermoregulation has also recently been proposed as a possible function for the
_Triceratops_ frill.

And of course, the large frill over the neck would put the head's center of
balance over the foramen magnum (the hole in the skull where the neck bones
attach).  This may have facilitated forcefully swiveling the head, though at the
expense of a considerable mass of bone!

There are probably other hypotheses, but this is what I can remember at this
time.  You can find plenty on this in the archives, I'm sure, as the topic has
come up before.

I don't know if any of today's paleontologists are reviving the older hypotheses
that you mention.

-------Ralph W. Miller III
           ralph.miller@alumni.usc.edu