Re: Taxonomic Status

["Andy Farke" <andyfarke@hotmail.com>]

> In a message dated 12/9/01 8:46:52 AM Pacific Standard Time,
> j_mallon@hotmail.com writes:
 > << To paraphrase,
> there are three specimens from western Canada (one of which is just a
> "posterior parietal bar") that show _C. irvinensis_ as having had an oddly
> "squared off" frill and comparatively smaller parietal fenestrae than
other
> members of its genus.  I'm sure there are more distinctions that can be
> made, but that's as far as I'm willing to go without having seen the
paper. >>
>
>
>        If I remember correctly, I believe _C. irvinensis_ is also younger
> stratigraphically. DV

The abstract (available at
http://www.nrc.ca/cgi-bin/cisti/journals/rp/rp2_abst_e?cjes_e01-036_38_ns_nf
_cjes10-01) says the following:

"Chasmosaurus irvinensis (sp. nov.) is distinguished from other species of
this genus by the possession of a broad snout, absence of a brow horn (the
position of which is occupied by a pit or rugosities suggestive of bone
resorption), broadly rounded and open jugal notch, subrectangular squamosal,
straight posterior parietal bar bearing 10 epoccipitals, eight of which are
flattened, strongly curved anterodorsally, and nearly indistinguishably
coossified to their neighbours, and small, transversely oriented parietal
fenestrae restricted to the posterior portion of the frill."

A very cool-looking ceratopsian. I'd been hearing about it for the last few
years, in which it was referred to as the "potato-chip chasmosaurine,"
because the frill's caudal border is sorta curled up like a potato chip.

I'm not sure if I like absence of brow horns as a specific character. . .my
suspicion is that they were small but present in young adults, and got
resorbed with age--the authors acknowledge this in the paper, too.
Postorbital horn resorption is common in many centrosaurines--Ryan et al.
nicely outline this in their paper on the Centrosaurus bonebed (Palaios,
2001, v. 16, p. 482-506).

Best,

Andy
_______________________________
Andrew A. Farke
South Dakota School of Mines and Technology, Box P404
501 East St. Joseph Street
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