Feduccia on Prum and Cryptovolans (i.e., Microraptor)

[bh480@scn.org]

From: Ben Creisler bh480@scn.org

Alan Feduccia's commentary on Prum "Birds are Dinosaurs: 
Simple Answer to a Complex Problem." (The Auk: Vol. 119, 
No. 4, pp. 1187-1201 (2002))  restates a number of  
objections to the birds as derived theropods. He puts 
special emphasis again on teeth:
"Perhaps the most impressive difference between theropods 
and birds concerns the structure of teeth and the nature 
of their implantation . It is astounding that more 
attention has not been given to the dramatic differences 
between bird and theropod teeth (especially when one 
considers that the basis of mammal paleontology involves 
largely tooth morphology.) 
"To be brief, bird teeth ....are remarkably similar and 
are unlike those of theropods. Mesozoic bird teeth share 
numerous remarkable similarities with crocodilians, but 
not found in theropod dinosaurs. The typical bird and 
crocodilian tooth is characterized as having a flattened, 
unserrated crown that becomes constricted as it approaches 
the crown?root juncture. The tooth narrows at that point 
and then there is an expanded root crown with a cement-
covered root at least as broad as the crown, usually 
broader. Details of the differences in morphology, 
implantation, and replacement can be found in Martin et 
al. (1980) , and Martin and Stewart (1999) . It is 
noteworthy that the Upper Jurassic bird?dinosaur ?missing 
link? of 1991 was Lisboasaurus ,later shown to be a 
crocodilomorph (Feduccia 1999 )......"

However, the differences in size and diet  between early 
toothed birds and theropods are not addressed, nor the 
presence of conical unserrated teeth in some theropods  
(spinosaurs), probably a diet-related feature.

Perhaps the real news in his commentary is a serious 
consideration of the dromaeosaurs-as-birds hypothesis, 
which would seem to contradict his comments about teeth!

"There are also asymmetric flight feathers preserved on 
the wing and near the hind limbs of a dromaeosaurid 
(Norell et al. 2002 , Czerkas et al. 2002 ). Given the now 
substantial evidence that certain taxa once thought to be 
dinosaurs (e.g. Caudipteryx ,  Protarchaeopteryx >, and 
the Oviraptosauria; Maryanska et al. 2002 ) are most 
likely secondarily flightless birds, and the new 
hypothesis that certain dinosaurs were secondarily 
flightless descendants of Mesozoic birds (Paul 2002 ), we 
must now carefully consider the possibility that there may 
have been a number of radiations of secondarily flightless 
Mesozoic birds that evolved morphologies quite similar to 
theropod dinosaurs.
"This view is now endorsed by Czerkas et al. (2002) who 
describe the Chinese early Cretaceous Cryptovolans pauli , 
characterized by the presence of asymmetric, primary 
flight feathers, avian hand, and sternum, but with typical 
dromaeosaur-like teeth, a hypertrophied second sickle 
claw, and dromaeosaur-like stiffened tail. Such a 
specialized, derived tail is virtually the same in 
rhamphorhynchoid pterosaurs of the Jurassic.
"It has become clear that this problem is far more complex 
that those on either side of the debate had anticipated, 
and the real challenge now may be to separate out 
radiations of secondarily flightless birds from true 
theropods. And, if birds are, as Paul (2002) argues, 
derived from theropods and then gave rise to secondarily 
flightless theropods, the problem of convergence is simply 
transferred to dromaeosaurs and carnosaurs. Such a 
convergent pattern may be even more formidable than that 
proposed between flightless birds and theropods. Either 
way, if birds were initially derived from dromaeosaurs, 
then the required character transformations involved going 
from highly derived sickle second claw to primitive avian 
claw, highly derived stiffened tail to primitive 
Archaeopteryx-like tail, and highly derived theropod teeth 
to primitive bird teeth.......
"If, as proposed by Paul (2002) and Czerkas et al. 
(2002) , dromaeosaurs are actually birds, either 
flightless or becoming flightless, then the question of 
bird origins is again completely reopened. But aside from 
the obvious problems, that proposal has major implications 
because both camps in the debate would have portrayed 
dromaeosaurs incorrectly, and as Czerkas et al. 
(2002 :120) note, ?cladistics has presented a highly 
misleading interpretation of the evidence,? and (p. 
122) ?The origin of birds stems further back to a common 
ancestor of pre-theropod status.? If correct, whatever the 
case, the presence of Cryptovolans as a dromaeosaur with 
fully developed flight feathers, an avian style hand and 
sternum, dromaeosaur teeth, sickle claw, and a stiffened 
dromaeosaur (rhamphorhyncoid) tail, should send all those 
involved in the debate on bird origins back to the drawing 
board."

Added to Olson's use of the term "bird" (perhaps 
inadvertent) when referring to the feathered Microraptor 
gui specimens in an NPR interview last week, it is no 
longer clear exactly where Feduccia and Olson stand on 
dromaeosaurs. If they accept the presence of true feathers 
in dromaeosaurs, they apparently would consider them to be 
theropod-like birds, not derived from coelurosaur 
theropods but from some more distant pre-dinosaur 
ancestor.  Let the fossils keep coming!