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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 coelurosaurs;>>

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 siphonium.)

      <<(2) the lack of clear evidence of a fenestra rotundum in coelurosaurs;>>

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 flight;>>


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 think).

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 this argument.

Difference does not indicate non-relationship.

Matt Troutman
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