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At 12:42 PM 1/31/97 -0600, you wrote:
>>From recent listmail I see that Gorgosaurus libratus seems to be preferred
>now to Albertosaurus libratus. How did this come about--I obviously missed
>it? A paragraph of enlightenment would be much appreciated.
I can give you both the cladist's and the gradist's answer to the question.
Cladist: With the possible exception of a few ectopterygoid characters,
every feature used by Russell, Carpenter, and Paul to unite Gorgosaurus and
Albertosaurus are *primitive* characters. However, primitive characters do
not indicate special affinities; they are simply those features inherited by
the common ancestor and not subsequently transformed. (For example,
possession of three horns does not especially unite Triceratops with
Torosaurus, since this characteristic is shared among all ceratopsines (and,
even more broadly, with Ceratopsidae in general)). Since there is no
compelling evidence that Gorgosaurus and Albertosaurus uniquely share a
common ancestor outside of all other tyrannosaurids, and given the disfavor
with which most cladists regard paraphyletic genera, the name "Gorgosaurus"
for the Judith River form is to be retained.
Gradist: Albertosaurus sarcophagus is quite a distinct form from
Gorgosaurus libratus. Unfortunately, there are few skulls of A. sarcophagus
on display (or even available in popular books), so the short-snouted,
bulldoggedness of A. sarcophagus is not well appreciated. Morphologically,
Gorgosaurus is at least as distinct from Albertosaurus as Daspletosaurus is
from Tyrannosaurus, so if both the latter two generic names are retained,
both the former two should be. (The alternative, which Greg Paul advocated
in Predatory Dinosaurs of the World, is to sink Gorgosaurus into
Albertosaurus AND to sink Daspletosaurus into Tyrannosaurus).
Note: neither of these arguements have been published yet, but are in
Thomas R. Holtz, Jr.
Vertebrate Paleontologist Webpage: http://www.geol.umd.edu
Dept. of Geology Email:email@example.com
University of Maryland Phone:301-405-4084
College Park, MD 20742 Fax: 301-314-9661
"To trace that life in its manifold changes through past ages to the present
is a ... difficult task, but one from which modern science does not shrink.
In this wide field, every earnest effort will meet with some degree of
success; every year will add new and important facts; and every generation
will bring to light some law, in accordance with which ancient life has been
changed into life as we see it around us to-day."
--O.C. Marsh, Vice Presidential Address, AAAS, August 30, 1877