[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
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!
Dr Timothy J. Williams
Iowa State University
Ames IA 50014
Phone: 515 294 9233
Fax: 515 294 3163
Get your FREE download of MSN Explorer at http://explorer.msn.com