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Re: Scaly tyrannosaurs; fact or fiction?



Nick Pharris wrote-

> Um, a lot of these look size-related to me, kinda like the ones that used
to
> land the tyrannosaurs in the Carnosauria.

Well, let's see here.  It's hard to find small non-coelurosaurian theropods
to compare with, in order to test if a character's size-related or not.  I
think you'll agree Eoraptor (assuming it's theropod), coelophysoids and
noasaurids are good subjects for this analysis, as they are small and
outside the Coelurosauria.  If a feature is size-related, we would expect it
to be present in small taxa despite their classification.  So, character 1
(nasal subequal to frontal) is absent in both Eoraptor and coelophysoids.
This suggests the character is not size-related, but rather phylogenetically
useful.  Character 2 (orbit longer than antorbital fenestra) is present in
Eoraptor, but absent in coelophysoids.  As coelophysoids lack this
character, it doesn't seem to be size-related, but may need some working
out.  Character 3 (laterotemporal fenestra dorsoventrally shorter than
orbit) is lacking in both Eoraptor and coelophysoids, so it is not
size-related either.  Finally, character 4 (low cervical neural spines), is
present in Eoraptor, coelophysoids and Noasaurus.  While at first, this
looks suggestive of size-relatedness, remember large taxa (abelisaurids)
sometimes also exhibit this trait, while some small taxa (Ornitholestes,
small dromaeosaurids) lack it.  This would seem to indicate it is also
useful phylogenetically.

> Oh, and last time I looked, tyrannosaurs had ventrally-projecting pubic
> peduncles.

This is largely relative.  Tyrannosaurids obviously have more vertical pubic
peduncles than Allosaurus, but seem comparable to Piatnitzkysaurus to me.
On the other hand, Sinosauropteryx (see my photo on the Dinosauricon) has a
much more vertical peduncle.  Also, the fact Stokesosaurus comes out as a
basal tyrannosaur in my cladogram (and has an obviously anteroventrally
pointing pubic peduncle) may have influenced the coding.

Mickey Mortimer