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Re: Dinosaurs with Pygostyles
At 05:33 AM 16/01/2000 -0800, Jaime A. Headden wrote:
Barsbold R.; Currie, P.J.; Myhrvold, N.P.; Osmólska,
H.; Tsogtbaatar K.; and Watabe M. 2000. A pygostyle
from a non-avian theropod. Nature 403: ???-???.
You realize, of course, what this will lead to.
Last week, while in DC, I dropped in to see Storrs Olson (on a
non-bird-origins matter!). He very kindly gave me a copy of a new
publication he has edited:
Olson, Storrs ed. 1999. Avian Paleontology at the close of the 20th
century: Proceedings of the 4th International Meeting of the Society of
Avian Paleontology and Evolution, Washington, DC, 4-7 June
1996. Smithsonian Contr. Paleobiology 89. 344 pages.
Of course, given the date of the conference, these papers are reflective of
the pre-Sinosauropteryx etc. state of affairs. Nonetheless dinopersons
will probably want to read at least the concluding section on Mesozoic
Birds and Early Avian Evolution, consisting of seven papers and reports on
four roundtable discussions.
Anyway, one of these is a paper by Andrzej Elzanowski, "A comparison of the
jaw skeleton of theropods and birds, with a description of the palate in
the Oviraptoridae". The abstract reads:
"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
omithurine 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 Ichthyomithidae and
Hesperornithidae may be interpreted as synapomorphies supporting monophyly
of the Odontognathae."
Specifically, the author notes four characters shared by oviraptors and
ornithurines not found in Archaeopteryx: Articular with Iateral process;
Articular with medial process; Mandibular symphysis fused; Jugal bar
rod-shaped. He concludes that: "These suggest that the oviraptorosaurs
branched off after Archaeopteryx and thus represent the earliest known
flightless birds. Except for the elongate forelimbs (which become shortened
in all flightless forms), the postcranial skeleton of Archaeopteryx does
not have any avian traits that would be absent in the oviraptorids .
Therefore, if flightlessness had evolved at a stage of avian evolution
close to Archaeopteryx this would be extremely difficult to distinguish
from the primary flightlessness of the theropods."
The author certainly does not doubt that birds are derived from theropods -
he is not in the Olson-Feduccia-Martin camp. However, if he is right not
only can Greg Paul (and George Olshevsky - BTW, both their views get
mentioned in one of the round tables) rejoice, but Larry Martin will
certainly be able to say "I told you so" when he claims Caudipteryx (and, I
assume, the new "feathered" therizinosaurid whose name I am incapable of
spelling) are birds and thus are of no use in determining feather origins.
And to bring this back to the first point, a pygostyle in this group would
certainly be consistent with oviraptorids being derived birds.
Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2 mailto:email@example.com