[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Tarsitano's challenges
<<"The following morphological problems involving the theropod
ancestry of birds must be addressed by those who favor a
coelurosaurian ancestry or sister-group position for birds:
(1) the absence of a siphonium and pneumatic quadrate in all
Found in carcharodontosaurs, tyrannosaurs (coelurosaurs, not carnosaurs
according to Tarsitano), and oviraptors. (If memory serves, some recent
troodontids and velociraptorines have been found with a quadrate-articular
<<(2) the lack of clear evidence of a fenestra rotundum in
Tarsitano has his own definition of the fenestra pseudorotunda (which he
calls the fenestra rotunda for a stupid reason), which not surprisingly
excludes theropods. The fenestra pseudorotunda appears to be at least a
basal maniraptoran feature, if not a basal theropod feature.
<<(3) nonavian tooth morphology in coelurosaurs;>>
By this he means teeth that are not triangular, peg-like, and have
replacement pits, like that of _Archaeopteryx_ and crocodylomorphs.
Juvenile theropods have birdlike teeth, sans the replacement pits.
<<(4) reduced coracoids in all coelurosaurs;>>
A lie. Coelurosaurs, even tyrannosaurs, have deep, birdlike coracoids with
prominent biceps tubercles (acrocoracoids of birds) swept back caudally.
<<(5) the presence of a massive and specialized pelvis and
hindlimbs that, biomechanically, seem to argue against the devlopment of
Need we mention velociraptorines?
<<(6) the presence of the middle temporal arch in coelurosaurs, but
its absence in birds;>>
This is my favorite. Using this criteria, all archosaurs, archosauromorphs,
most neodiapsids (including lepidosaurmorphs) would be excluded from a
relationship with birds. Besides, _Archaeopteryx_, Confuciusornis_, and the
enantiornithines have a middle temporal arch.
<<(7) the presence of lateral basicranial sinus openings in
coelurosaurs, but their absence in birds.>>
Dubious. This is based on the lateral concavity on the braincase of
_Troodon_, which is only seen in some oviraptors, and therizinosaurs (I
The list above is basically a continuation of the birds-can't-be-dinosaurs
camp's tactic of assuming difference in anatomy indicates non-relationship.
Some examples, such as the propubic pelvis and the middle temporal arch, are
just silly as they are being very myopic by not acknowledging that at some
point in bird evolution, birds would have sister-groups with a propubic
pelvis or a middle temporal arch (basically a postorbital-squamosal
articulation). Basically, because birds differ from theropods some details
(these themselves are debateable), they cannot be related to them.
Tarsitano and Hecht (1980), Hecht and Tarsitano (1982), Hecht (1985),
Tarsitano (1985a,b), Tarsitano (1991), and Hecht and Hecht (1994) all show
Difference does not indicate non-relationship.
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com