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Re: Triceratops

Brian Choo (bchoo@cyllene.uwa.edu.au) responds to Steve
Brusatte, who wrote:

<<I find it hard to believe, in a strict biological sense, that
four different species of the same genera would inhabit the same
area. I do know that some of the Psittacosaurus species are from
different times, but this notion is still hard to believe. 
Dodson, in his book, repeats the fact that there is only one
species of giraffe, one species of hippo, and one species of
rhino in Africa today. If there were 8 or 10, then all of the
species would be competing for the same general foods and
something would go extinct.>>
<Well, such a high diversity of one species is unusual but far
from unprecedented. Using extant macropod marsupials as an
analogy, the following species of Macropus>

  [the list is snipped, sorry, Brian]

  The relative ecology of the psittacosaur species may also have
a strong reflection in their speciation; as Pete Buchholz wrote,
the jaws of psittacosaurs are varied slightly, and it is more
than likely that the most basal psittacosaur (stem psittacosaur)
bore premax teeth, lost on the psittacosaurid diversity we
recognize now. Beak shape, jaw form and also apparently position
of the adductors and depressors, vary, and tooth morphology has
also been used to separate some species, as does count. A wider
anterior half of the jaw with a deep profile will probably infer
a stronger hyomandibular and lingual musculature than other
species, and this, too, is important.

  Varied jaw actions and morphology may then corrolate to diet,
as is often inferred in pterosaurs and mosasaurs, and known in
varanids, carnivorans of similar mein (esp., canids and
pinnipeds [sensu lato]) etc.. Thus, each contemporaneous species
may have had a more specialized diet than another. It's the
generalists you have to e very careful about, as pure
generalists (omnivores, opportunists) tend not to overlap
ecologically (crows versus raccoons don't count, as one is
terrestrial and the other arboreal/aerial).

  Size also will be a factor: *Macropus* species, as Brian Choo
points out, tend to vary in size a great deal, some canids
(various vulpines and aureines [my word for jackals]) will
coexist and be size specialists as well as niche partitioning.
Vultures are another example of size and strict diet
specialists, where a single carcass can be visited by more than
one species, but not one overlapping the other's food of choice.

Jaime A. Headden

  Where the Wind Comes Sweeping Down the Pampas!!!!

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