Comment on "Embryological evidence identifies wing digits in birds as digits 1, 2, and 3."

Xing Xu, Xing Xu, Jonah Choiniere, Corwin Sullivan, Fenglu Han
2011 Nature Precedings  
Tamura et al. (Science, 11 Febuary 2011, p. 753) claim that the three avian wing digits should be identified as digits I-III based on new embryological data and suggest that these identifications help to remove the conflict between the paleontological data and developmental data concerning the homology of the avian digits. However, their results are not novel, and the authors fail to address the critical problems relating to this interesting issue. Tamura et al. 1 provide embryological data on
more » ... igital development in living birds. They claim that the three avian wing digits should be developmentally identified as digits I-III and suggest that these identifications help to remove the conflict between the paleontological data and developmental data concerning the homology of the avian digits. While Tamura et al. present information of significance, their study fails to address larger questions of digit homology and the paleontological record. First, the authors state without discussion that paleontological data indicate the loss of digits IV and V in extinct and living tetanuran theropods, but they do not mention published evidence to the contrary. Previous studies have provided morphological evidence supporting a II-III-IV identification for the three manual digits of extinct tetanuran theropods 2 . Our recent study demonstrates a decoupling of morphological features in the hands of extinct tetanuran theropods (including the earliest known birds): most metacarpal features support a II-III-IV identification and most phalangeal features support a I-II-III identification 3 . The updated paleontological data thus clearly contain two contradictory signals relating to the identification of the tetanuran manual digits. The strikingly conservative phalangeal formula of 2-3-4 seen in tetrapods has been given primacy in identifying these digits as I-II-III, overshadowing other morphological features that favor the II-III-IV identification. The significance of the latter evidence for the problem of digital identification was only recognized following the recent discovery of the unusual theropod Limusaurus, which has a vestigial digit I 3 . Second, some important embryological data have not been fully appreciated by Tamura et al., which weakens the significance of their study. Given that several recent embryological studies also support the I-II-III hypothesis 4, 5 , the authors' identification of the avian wing digits as I-II-III is not novel. Furthermore, except the embryological evidence from the primary limb axis, there are other lines of evidence supporting a II-III-Nature Precedings :
doi:10.1038/npre.2011.6433.1 fatcat:7uriugcodrfmzagknbxvhwvloq