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RE: The Back-up New Papers

Jerry Harris wrote-

> Vickaryous, M.K., and Hall, B.K. 2010. Comparative development of the
> crocodylian interclavicle and avian furcula, with comments on the homology
> of dermal elements in the pectoral apparatus. Journal of Experimental
> Zoology 314B:196-207. doi: 10.1002/jez.b.21326.
> ABSTRACT: The pectoral apparatus (shoulder girdle plus sternum) of amniotes
> plesiomorphically includes an unpaired element of dermal origin. In
> crocodylians, lepidosaurs, and nontherian synapsids (monotremes and their
> ancestors) this element is identified as the interclavicle, in Testudines
> (turtles and tortoises) as the entoplastron, and in Aves as the furcula. We
> investigated embryonic development of the interclavicle in Alligator
> mississippiensis (American alligator) and of the furcula in Gallus gallus
> (domestic chicken). The interclavicle and furcula are among the first
> skeletal elements to ossify, beginning at Ferguson stage 19 (Alligator) and
> Hamburger and Hamilton stage 33 (Gallus). Both elements: occupy a similar
> mid-ventral position within the pectoral apparatus; develop from paired
> (bilateral) cell condensations; never coexist at anytime during ontogeny or
> in the adult; and undergo intramembranous (i.e., direct) ossification. For
> both the interclavicle and the furcula, the initial onset of ossification is
> concomitant with mineralization of elements of the dermatocranium, and
> occurs in advance of mineralization of the replacement bones (e.g., scapula,
> metacoracoid) of the pectoral apparatus. Shortly after the initiation of
> ossification the paired condensations of both elements fuse. For each of
> Alligator and Gallus, only one pair of skeletogenic condensations is present
> during embryonic development. Based on these data and a review of the
> evolution and development of dermal elements in the pectoral apparatus, we
> conclude that the interclavicle is equally parsimonious as a homolog of the
> furcula.

Er... I haven't read the paper yet, and development is not my forte, but 
theropod outgroups like Massospondylus clearly show a furcula homolog that is 
unfused clavicles (Yates and Vasconcelos, 2005), while the basal archosaurian 
interclavicle (e.g. Erpetosuchus) is an unpaired xiphoid element.  Also, unlike 
modern crocodilians, basal crurotarsans have both clavicles and an 
interclavicle.  Clavicles are THE first elements to ossify in the pectoral 
girdle in squamates, have a more similar position to the furcula, also develop 
from paired condensations, also never coexist with furculae, and also undergo 
intramembraneous ossification.  Is it just me, or does this hypothesis ignore 
paleontological evidence as much as the recent "theropods have manual digits 
II-III-IV" paper did?
Mickey Mortimer
The Theropod Database Blog- http://theropoddatabase.blogspot.com/