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From: email@example.com (Steve Jackson)
> Stan Friesen wrote:
> > I do not think this is conclusive, at least if _T. horridus_ is
> > the female morph. In an animal with a harem type herding system
> > females may well be substantially more common than males.
> True as far as it goes, but is there any evidence of Triceratops being a
> herd animal?
I would say yes, though it is mostly circumstantial:
- Many ceratopsians are known from mass death sites under circumstances
that strongly suggest herding.
- The structure of Triceratops fill and horns stongly suggests
intense intraspecific competition, which is usually found in forms
with a harem structure: one dominant male with several females,
as in living wild horses.
> I know it gets illustrated that way, but I was under the impression
> that there are no known Triceratops bonebeds; finds have been
> single. Is this so?
Yes, but most finds of ALL ceratopsians are single. Bone beds are
the exception for all of them.
Now for some added comments. I have now read Forster's article.
She did something I would not have beleived possible, she convinced
me that Diceratops is indeed distinct from Triceratops. (If it were
nmot for its short frill I would transfer it to Torosaurus, however).
Now, as for the two species of Triceratops, the evidence is still
a little ambiguous, but I would say it tends to favor separation
at the species level.
First, one of the anatomical differences she describes is in fact
potentially sufficient to allow ecological differentiation even though
she does not seem to realize this (or at least in the one point where
she mentions the possibility of ecological difference she fails to
cite her own descriptions).
She states (and her data backs her up on this) that T. prorsus has
a shorter, narrower, deeper beak than T. horridus. The diferences are
(just barely) large enough to support a difference in feeding
preferences. This data suggest that T. prorsus was slightly more
selective a feeder than T. horridus - perhaps specializing in younger,
more nutritious shoots, or perhaps in fruits.
This factor is only "permissive", as sexes in dimorphic species
are often ecologically distinct in just this manner. (Check out
house sparrows in the USA for an example).
The second factor that militates against a single species is the
fact that the rarer morph - T. prorsus - consists entirely of specimens
previous suggested as *females*, while T. horridus includes specimens
previously identified as both genders. [In the paper in the symposium
on Dinosaur Systematics from a few years ago describing the mass death
site for a species of Chasmosaurus from Texas]
If Forster's T. prorsus had corresponded to the males of the prior
analysis I would have leaned towards a single species. As it is I
am now slightly favoring two species.
The peace of God be with you.