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New interpretation of the hands of tetanurans and *Limusaurus*
/*Limusaurus/* is a remarkable herbivorous ceratosaur unique among
theropods in having digits II, III and IV, with only a small metacarpal
vestige of digit I. This raises interesting questions regarding the
controversial identity of avian wing digits. The early tetanuran
ancestors of birds had tridactyl hands with digital morphologies
corresponding to digits I, II & III of other dinosaurs. In bird embryos,
however, the pattern of cartilage formation indicates that their digits
develop from positions that become digits II, III, & IV in other
amniotes. */Limusaurus*/ has been argued to provide evidence that the
digits of tetanurans, currently considered to be I, II and III, may
actually be digits II, III, & IV, thus explaining the embryological
position of bird wing digits. However, morphology and gene expression of
the anterior bird wing digit specifically resemble digit I, not II, of
other amniotes. We argue that digit I loss in /*Limusaurus/* is derived
and thus irrelevant to understanding the development of the bird wing.
Haven't read the paper yet, will do so soon.
This is Nature Precedings. A longer paper is in the works, but won't be
published in Nature, which rejected the manuscript downloadable at the
link given above because it's allegedly not interesting enough.
Courtesy of comments 176 and 178 in this thread: