New papers (relevant to bird origins)

["Tim Williams" <twilliams_alpha@hotmail.com>]

Two recent papers caught my interest, neither of which I have read (beyond 
the abstract anyway).  My apologies if these have been mentioned before....

The first is by DML listmember, Renesto Silvio.  It has some interesting 
thoughts on the identity of the skull of _Protoavis_.

Silvio, R. (2000).  Bird-like head on a chameleon body: New specimens of the 
enigmatic diapsid reptile Megalancosaurus from the Late Triassic of Northern 
Italy.  Rivista Italiana di Paleontologia e Stratigrafia. 106 (2): 157-180.

Abstract reads:  Two new Megalancosaurus specimens collected from the Norian 
(Late Triassic) Calcare di Zorzino (Zorzino Limestone) Formation (Bergamo, 
Lombardy, Northern Italy), and from the coeval Dolomia di Forni (Forni 
Dolostone) Formation (Udine, Friuli, North-eastern Italy) improve our 
knowledge of skeletal anatomy and mode of life of this genus. Morphology of 
observable skull elements and cervical vertebrae in one of the new specimens 
shows some resemblance to the possible Triassic bird Protoavis, while the 
postcranial skeleton of Megalancosaurus is completely non-avian. This may 
suggest that either Megalancosaurus and Protoavis developed a similar neck 
structure as a response to the same functional requirement, or that part of 
the disarticulated material ascribed to Protoavis may indeed belong to a 
Megalancosaurus-like reptile. Megalancosaurus shows a very high adaptation 
to arboreal life and a peculiar feeding strategy. Recent suggestions that 
Megalancosaurus may have been a glider and a possible model for bird 
ancestry are discussed. Some skeletal features of Megalancosaurus may indeed 
be interpreted as gliding adaptation, but evidence is weak, and if this 
reptile was a glider, however, its gliding bauplan should have been 
completely different from the one usually accepted for bird ancestors, 
showing instead more morphological similarities with gliding squirrels, 
phalangeriids and putative ancestors of bats and pterosaurs (according to a 
non cursorial model for these latter).


The second paper concerns Andrezj Elzanowski's view on the close 
relationship between ornithurine birds and oviraptorosaurs.  Andrezj has 
being pushing the idea that oviraptorosaurs are flightless birds (and closer 
to ornithurines than _Archaeopteryx_ is) for a while now. I wonder if the 
discovery of feathers in one oviraptorosaur (_Caudipteryx_) and a pygostyle 
in another (_Nomingia_) puts a new spin on this idea.  I'll try to track 
down the paper this afternoon.  From the abstract (and I could be wrong), 
the implication is that _Archaeopteryx_ is being pushed further down the 
theropod tree by Andrezj, outside of a clade that includes 
Ornithomimosauria, Therizinosauria, Oviraptorosauria and Ornithurae.

Elzanowski, A. (2000).  A comparison of the jaw skeleton in theropods and 
birds, with a description of the palate in the Oviraptoridae.  Smithsonian 
Contributions to Paleobiology. 1999 (89): 311-323.

Abstract: Similarities to birds in the structure of the jaws and palate 
suggest that oviraptorosaurs (oviraptorids and caenagnathids), 
therizinosauroids, and ornithomimosaurs are the closest theropodan relatives 
of birds, which is in conflict with recent phylogenetic reconstructions 
based on postcranial evidence. No specific avian similarities could be found 
in the jaws and palate of dromaeosaurids. The ectopterygoid of the 
oviraptorids connects the lacrimal to the palatine, as does the avian 
uncinate (lacrimopalatine). This and other cranial similarities between the 
oviraptorosaurs and ornithurine birds raise the possibility that 
oviraptorosaurs are the earliest known flightless birds. With Archaeopteryx 
and the theropods providing evidence of plesiomorphic conditions, 
similarities in the mandibles, teeth, and tooth implantation in the 
Ichthyornithidae and Hesperornithidae may be interpreted as synapomorphies 
supporting monophyly of the Odontognathae.

Have a great Christmas everyone!


Tim

------------------------------------------------------------

Dr Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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