CKing wrote:
>>...One of the most strongly held cladistic dogma is that birds are descendants of a bird-like, advanced theropod. John Ruben and his students ... have also shown that a baby theropod (Scipionyx) had a hepatic piston breathing system, but not the air sacs of birds, dealing a severe blow to the "birds are dinosaurs" dogmatists, since it is impossible to derive the air sac system from the hepatic piston system, given the fact that the intermediate animal would have a life threatening hernia or hole in its diaphragm. Birds, it would appear, could not have evolved from a theropod based on this fact alone.
>>

Me:
IF all the premisses are admitted, the conclusion is still fallacious. This argument could, at most, only show that birds were not descended from Scipionyx. CKing's argument, at least, does not even need refutation. (I haven't read all of Ruben yet, but there are, for example, numerous modern exceptions to the correlation of nasal turbinates and endothermy; e.g., Seymour et al's paper in the year-end issue of Physiological and Biochemical Zoology)

CKing:
>>Nevertheless, the cladists march on, oblivious to the accumulating evidence that their theory of the theropod origin of birds has been refuted. Then in 2000, one of Ruben's students published a startling discovery in the journal Science along with a long list of scientists. The fossil Longisquama was brought to the US from Russia for an exhibition for the first time, after the end of the cold war. With scientific equipment not available to most Russian scientists, Longisquama, a lizard-like creature found originally in Central Asia by an entomologist, was found to have feathers on its back. And the feathers share so many unmistakable anatomical and developmental details with bird feathers that it shocked the cladists, who scrambled to come up with all sorts of weird and scientifically untenable explanations to deny an obviously close relationship between Longisquama and birds. Even those cladists who are not actively doing research on the question of bird origin felt compelled to voice their opposition to the newly discovered evidence that birds are not descended from a two-legged theropod dinosaur, but from a small, 4-legged archosaurian reptile which has not evolved into a dinosaur. This discovery shows that cladistic analysis is flawed because time and again cladists have come up with the same erroneous answer that birds are descendants of an advanced theropod dinosaur when they are obviously not to anyone who is reasonable and rational.
>>

Me: reasonable and rational??? 'Fraid not, mate.
In palaeontology, we can get quite a lot of information on relationships from the skeleton of well-preserved fossil vertebrates; and this information has always supported descent of dinosaurs from birds (there was a period starting with Heilmann 1923, when most of the synapomorphy was attributed to convergence based on the supposed lack of furcula in dinsaurs, now known to be both illogical and factually wrong).
Arguments based on feathers, developmental dogma relating to homology of digits etc. have been regarded as conclusive refutations of the skeletal evidence, but not by anybody who actually performs any kind of analysis of the data, beyond hand-waving .
And IF Longisquama has feathers homologous to those of birds, it does not show that Longisquama is ancestral, but that feathers originated before dinosaurs; of course this is fully consistent with birds descending from theropods. CKIng seems to have totally missed the flight feathers (on arms, legs and tail) of the dromaeosaur Microraptor gui (Xu et al. 2003, Nature 421: 335-340) which actually make Longisquama irrelevant to bird ancestry (but still interesting for the evolution of feathers, which is a totally different question).
So, dromaeosaurs (Velociraptor and friends) had feathers on their hands, and small ones could at least glide (Xu et al.). Then, SO WHAT if Longisquama had a row of feathers down the middle of its back? - by position, they cannot be homologous to bird FLIGHT feathers, while those in Microraptor apparently are. And, oh yes, that just happens to coincide with what the skeletal evidence says: birds are theropods.


-----
John D. Scanlon
Riversleigh Fossil Centre
Outback at Isa
Mount Isa, Queensland, Australia
riversleigh@outbackatisa.com.au

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