Caudipteryx and the dark side

[Kendall Clements <k.clements@auckland.ac.nz>]

I enjoyed reading Jim Farlow's message from the dark side on September 
13, and finally had time to download the Jones et al. "Cursoriality in 
bipedal archosaurs" paper last week. Now that I've finished my first 
year teaching I have time for a postponed comment.

Tom Holtz (in a message on August 17) pointed out two methodological 
flaws with the above paper - (a) the use of restorations and 
reconstructions rather than fossils, and (b) exclusion of juveniles. I 
have a couple of more general comments relating directly to Jim's 
message, which I thought was a very honest and fair posting.

Jim wrote "The thoughts about the phylogenetic affinities of said beast 
are, in my opinion, a minor part of the paper." I can't agree. I think 
the paper adds little to the excellent work of Steve Gatesy, but what 
it does add uses a style of argument derived from a process-based 
evolutionary systematics viewpoint. This involves what Richard Dawkins 
calls "the argument from incredulity." In other words, if we can't see 
how something could have taken place, it can't have taken place. It 
hardly needs to be said that this is a highly subjective way of 
thinking, and this is one of the major reasons this sort of work has 
largely disappeared from the evolutionary literature. So while Jim 
could claim that the paper contains little direct phylogenetic comment, 
the whole package is highly tendentious. I'd guess that this is the 
reason one of Jim's colleagues described his (Jim's) choice of 
co-authors as "injudicious."

I take Tom's point that Caudipteryx requires more phylogenetic study, 
and suggest that this would have been far more productive than the 
approach taken by Jones et al. As with most of Ruben's work, it's not 
hard to find gaps in logic. First, Gatesy (1990) makes it quite clear 
that tail reduction preceded flight in theropod evolution, and 
consequently one could take issue with the idea that the shift in 
centre of mass in avians is to "provide stability during powered 
flight." To be fair, Jones et al. do consider alternative hypotheses, 
but the reader is left in little doubt where they should be looking for 
the answer, e.g. "We find it a striking coincidence that the only 
unambiguously feathered theropod was also the only known theropod 
likely to have utilized locomotory mechanisms identical to those of 
cursorial birds." Is Archaeopteryx not a theropod also?

I have real problems with (the latter part of) the statement "These 
observations might provide valuable clues about the lifestyle of 
Caudipteryx but they may also have implications for interpretation of 
its taxonomic affinities." This sort of thinking is about 20 years out 
of date. Apart from the subjective mode of evolutionary reasoning, 
there is also the problem of character independence. Jones et al. write 
"...none of these analyses has considered Caudipteryx's extensive suite 
of cursorial-bird-like locomotory characters." Functional complexes 
such as this may appear as a suite of characters, but they almost 
certainly are not. As Gatesy's work shows, tail reduction, development 
of the fourth trochanter, femur rotation and knee flexion are not 
independent.

In his posting Jim picked up on Tom's point about omitting juveniles: 
"Based on some work I did over the summer, however, I am not confident 
that S(inornithoides) and B(ambiraptor) can be disregarded in this kind 
of analysis, even if they are based on juveniles." Indeed, maybe what 
Ruben et al. see as a suite of bird-like characters are the correlated
consequences of paedomorphosis. Is there any evidence of this? Does the 
un-named oviraptosaur with a pygostyle show any changes in hindlimb 
dimensions relative to species with "normal" length tails?

I don't think Jim should feel too worried about the dark side. Remember 
how "The return of the Jedi" ended up!!

Kendall

----------------------
Kendall Clements
k.clements@auckland.ac.nz