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Since the subject of sexual dimorphism and detecting species ahas
popped up a couple time recently, I want some thoughts on species
resolution/ sexual dimorphism in _Triceratops_. Ostrom and Wellnhofer
showed pretty convincingly that most of the Tricertatops "species" can be
lumped into one, but Catherine Forster's paper in JVP last year seemed to
show pretty convincingly (at least, it seemed that way to me) there are
two distinct morphs.
However, Forster considered them to represent different species
rather then sexes for a couple of reasons I recall 1) they have the same
basal skull length, and 2) they are disproportionate in number. The first
seems dubious to me; could someone cite me specific examples of cases
where the males and females are about the same size? Moreover, and this
applies also to her second point, the sample size she used in her study
dopesn't seem large enough to give these arguments much weight, though she
may also be referring to more speciemns she didn't use in her study.
It was also recently pointed out to me that modern ungulates may
travel in same sex herds, or have differential mortality rates between
males and females, something that could be reflected in the fossil record.
I have been refereed to a book called "African Ungulates" by Walter
Leuthold, and articles in the African Journal of Wildlife.
Incidently, the "males" and "females" Lehman's paper in Dinosaur
Systematics identified for _Triceratops_ do not match up with Forster's
morphs; he identified them on the basis on the orientation of the horns,
something Forster found to be highly variable. Her morphs have different
horn LENGTHS, and she divied up her specimens differently.
"'Agnostic' is just 'Athiest' writ respectible".