[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Diceratops and Torosaurus (was: Aquatic Dinosaurs)
From: "Tim Williams" <T.Williams@cclru.randwick.unsw.edu.au>
> From Stan Friesen
> > This produces a fairly interesting chain:
> > basal Torosaurus => Diceratops => T. horridus => T. prorsus
> Except that Torosaurus has an extraordinarily long frill, and
> Diceratops and Triceratops both have short frills. Is it possible
> that Torosaurus and Diceratops both evolved from a common ancestor
> which had a medium-length frill - Arrhinoceratops maybe.
It is a fairly complex issue. Diceratops shares a short frill with
Triceratops and a couple of other skull apomorphies with Torosaurus.
Either there is a reversal in there somewhere, or at least one feature
evolved twice. By raw count (strict parsimony) the choice would be
two origins of a short frill - which would make Diceratops derived
from Torosaurus directly. However, with just three characters involved
I do not think parsimony is very useful. Besides I suspect the "two"
Diceratops-Torosaurus shared features may be functionally linked, and
thus constitute only one "effective" character" (they are certainly
similar in nature). This changes the parsimony count to a three-way tie.
Under the circumstances I am more inclined to believe reversal of the
minor Torosaurus features than multiple origins of a short frill in
an otherwise medium-to-long frilled group like the chasmosaurines.
The peace of God be with you.