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New papers (relevant to bird origins)




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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