|
Tom Holtz wrote:
> B) Almost all recent studies ally troodontids with
dromaeosaurids and birds
> rather than with ornithomimosaurs, so the
arctometatarsus is clearly
> convergent between these
groups.
The arctometatarsus may have evolved at many as *six*
times in theropod evolution: ornithomimids, tyrannosaurids, mononykines,
elmisaurids, avimimids, and troodontids. However, it is probable that two
or more of these groups share a common ancestry for the arctomet foot
- elmisaurids (?=caenagnathids)+avimimids, and
ornithomimosaurs+tyrannosaurs, for example. Also, the arctomet foot
(or an incipient version of it) might have arisen deep in coelurosaur phylogeny
and was subsequently refined or lost in individual theropod
lineages. Possibilities abound.
>
> 4) Is Confuciusornis dui still considered a valid species of
Confuciusornis?
> I'll get out my
species-ometer and check. --whoop whoop
> whoop--, Ah, well, inconclusive... :-) Chiappe et al.'s (1999) species-meter came to the same
conclusion (or same lack of conclusion). They do not affirm or deny the
validity of _C. dui_ (i.e. whether or not it is a synonym of _C.
sanctus_). The most distinctive feature of _C. dui_ is (said to be) the
upturned Woody Woodpecker-like beak evident in the keratinous outline
(not the bone underneath, though). Reading between the lines: (a) the
shape of the beak (cornified rhamphotheca) may not be unique to the _C.
dui_ type specimen (IVPP V11553) and may be present in _C.
sanctus_ too; (b) the unusual postcranial features ascribed to IVPP V11553
may prove to be absorbed by the broad intraspecific variation
reported for _C. sanctus_.
References
Chiappe, L.M., Ji S.-A.; Ji Q., and
Norell, M.A. (1999). Anatomy and systematics of the Confuciusornithidae
(Theropoda: Aves) from the Late Mesozoic of Northeastern China. Bulletin
of the American Museum of Natural History 242: 89pp. (A good
read)
Tim
-------------------------------------------------------------------
Timothy J. Williams, Ph.D. USDA-ARS Researcher Agronomy Hall Iowa State University Ames IA 50014 Phone: 515 294 9233 Fax: 515 294 9359 |