RE: TRICERATOPS AND PSITTACOSAURUS ARE NOT OVERSPLIT

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> -----Original Message-----
> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> T. Mike Keesey
> Sent: Thursday, March 08, 2001 9:14 PM
> To: -Dinosaur Mailing List-
> Subject: Re: TRICERATOPS AND PSITTACOSAURUS ARE NOT OVERSPLIT
>
>
> Six species for one genus is not that odd. _Equus_ has 6. _Canis_ has
> about 6. In some schemes, _Ursus_ has 6. _Felis_ has well over 6. I could
> go on for hours.

Furthermore, those are numbers for the Holocene: if you add in just the last
million years or so you can increase those numbers.

Compare this to the probably stratigraphic range for the _Psittacosaurus_
specimens in general (Barremian through Albian, but some possibly earlier)
and you have a LOT of time for speciation.

> It *is* a bit odd for a Mesozoic dinosaur genus (most of which have one
> valid species, if that), true.
>
But by the same token as above, almost all dinosaur "genera" are known from
a single formation (or, let's face it, from a single quarry...).

Had all _Psittacosaurus_ specimens been found from the same unit from a
limited horizon, I'd suspect that most or all the variation was normal
population variation.  However, since these specimens are scattered in time
and space, I suspect that at least some is actual taxonomic variation.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796