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Steadman's review of Mesozoic Birds



Published in the most recent issue of The Auk is a review of Mesozoic Birds:
Above the Heads of Dinosaurs. It's by David Steadman, who seems to be
slightly ABSRD (perhaps due to influence by Olson?), but as a neornithine
expert, does not actively work on Mesozoic fossils. I wanted to bash this
review, as it is such an entertaining activity, but David does a decent job.
Not great, but not a catastrophe of Feduccian proportions either. Still, I
have some complaints-

"There is much to recommend the theropod-to-bird (TB) hypothesis, as well as
considerable unresolved problems (see Feduccia 2002, Olson 2002)."
Apparently Witmer's opening chapter explaining the true status of these
"problems" wasn't effective enough. Indeed, Steadman later says of Witmer,
"He also attempts to refute some of the snags in the TB hypothesis that have
been raised by NTAB [non-theropod-archosaur-to-bird] researchers. I am not
sure, however, that his arguments will convince doubters, in part because of
a lack of photographs or illustrations, which would have helped a skeptical
reader to evaluate, for example, his assessment of what may or may not be
feathers in Cretaceous nonavian theropods." That's what the bibliography is
for, is it not?

"Either way, claims that that the TB hypothesis is "the only game in town"
(Lawrence Witmer, p. 19) or that the debate is waning (Livezey 2003) are not
accurate and therefore do little to further the TB cause."
Hehe, we'll see. Have there been any ABSRD papers since Prum (2003)
questioned the scientific status of Feduccia's arguments in Auk?

"(Recent assignment of the Early Cretaceous four-winged bird called
"Microraptor" to the Dromaeosauridae [Xu et al. 2003] is not substantiated
osteologically.)"
Though technically I agree (due to the PT definition of Dromaeosauridae, and
Microraptor/Cryptovolans oftentimes being avialan in my trees), I doubt I
would find any evidence Steadman uses for this statement compelling.

"In the next two chapters, Luis Chiappe, Mark Norell, and James Clark ("The
Cretaceous, Short-armed Alvarezsauride") and Fernando Novas and Diego Pol
("Alvarezsaurid Relationships Reconsidered") admit that alvarezsaurids
(Mononykus, Shuvuuia, Patagonykus, Alvarezsaurus, etc.), previously regarded
by TB researchers as birds, are reptiles. That determination had been made
already by Zhonghe (1995) and other authors."
lol "admit". Even ignoring that- First, some BAD proponents regarded
alvarezsaurids as non-avian from the beginning (eg. Ostrom, Sereno). Second,
I bet most of those BAD authors Steadman cited always believed
alvarezsaurids were reptiles (PT definitions again). Finally, though Zhou,
Martin, Sereno and such may have "determined" alvarezsaurids to be non-avian
prior to 2002, none had shown compelling reason this was a better hypothesis
(though Sereno 2001 made a good start).

"First, glancing at Chiappe and Walker's 20 "unambiguous synapomorphies" of
the extinct "Euenantiornithes" (p. 244), I noticed at least six characters
that can be found as well in some living species of birds.'
And I bet those living birds are separated from enantiornithines by at least
two other taxa without the characters, thus making them unambiguous
synapomorphies. Steadman seemingly doesn't understand unambiguous does not
mean un-paralleled, it means "can only most parsimoniously be applied to one
place in the cladogram".

"Part IV features a careful study by Anusuya Chinsamy, who documents a
fundamental difference in bone histology between ornithurine birds (rapid,
sustained rate of bone deposition) and nonornithurine birds (cycles of rapid
and then slow bone growth).  This information suggests that ornithurines,
which includes all living birds, as well as certain advanced Cretaceous taxa
such as Ambiortus, Hesperornis, and Ichthyornis, were endothermic but that
nonornithurines were not."
Oh, the simplicity. LAG's are found in neornithines too, and some non-avian
theropods lack them (Ricqles et al., 2001). It's going to take more than
LAG's to determine an organism's metabolism.

"Placing the late Cretaceous flightless South American Patagopteryx several
nodes within Aves might be controversial.  Lacking a reversed hallux (see
figure 13.25 C, E), Patagopteryx (covered by Chiappe in detail in Chapter
13) looks like a nonavian theropod to my Cenozoically biased eye."
Well, that's a new one. One would think the numerous derived characters and
widespread reasoning reversed halluces could disappear in terrestrial taxa
would be sufficient to place Patagopteryx securely in Aves. Interestingly,
I've found a few characters that would suggest Patagopteryx is
non-ornithothoracine (such as the significant portion of the coracoid still
present proximal to the acromion), though it's always closer to ornithurines
than enant-grade birds in my trees.

Finally, Steadman complains about the lack of abstracts and conclusion
sections, but mostly (half a page) about the preponderance of generic
abbreviations in the book. I never noticed this before, and had no problem
identifying which genus A. dementjevi or C. beishanensis were, but I suppose
I'm more familiar with these taxa than most readers would be. He says, "Most
genera of Mesozoic reptiles and birds are monotypic, so using an abbreviated
generic name with a species name, rather than just spelling out the genus,
not only saves no space (on average) but also conveys no more information."
True for the most part, but ironically, four of the six examples he uses are
polytypic in at least some of the authors' opinions (Archaeopteryx,
Confuciusornis, "Cathayornis", Anas).

Steadman does end on a positive note regarding the future of the BAD-ABSRD
debate, though I see it as more of a slow pathetic death of ABSRD
transforming to MANIAC transforming to BAD once prior ABSRDists sort out
their imagined chaos.

In conclusion, Steadman gets points for not sinking to the lows Olson (2002)
did in his cited review of the Ostrom Symposium volume. However, his review
also shows a lack of knowledge in Mesozoic taxa and cladistics (which might
be partially expected in a Cenozoic paleornithologist), and an undeserved
optimism towards ABSRD. One wonders what he thinks of the recent
backpeddling to MANIAC by Martin, Feduccia and others. In any case, I highly
recommend Mesozoic Birds to anyone interested in the dinosaur-bird debate,
coelurosaurs or uh... Mesozoic birds.

Reference- The Auk 120(4):1206-1208, 2003.

Mickey Mortimer