Conflicts of interest: None.
Commentary and Perspective
Metapodial or Phalanx? An Evolutionary and Developmental Perspective on the Homology of the First Ray's Proximal Segment
Article first published online: 2 MAY 2013
Copyright © 2013 Wiley Periodicals, Inc.
Journal of Experimental Zoology Part B: Molecular and Developmental Evolution
Volume 320, Issue 5, pages 276–285, July 2013
How to Cite
2013. Metapodial or phalanx? An evolutionary and developmental perspective on the homology of the first ray's proximal segment. J. Exp. Zool. (Mol. Dev. Evol.) 320B:276–285., , .
- Issue published online: 10 JUN 2013
- Article first published online: 2 MAY 2013
- Manuscript Accepted: 1 APR 2013
- Manuscript Revised: 29 MAR 2013
- Manuscript Received: 20 FEB 2013
- National Science Foundation. Grant Number: 0311768
- National Institutes of Health. Grant Number: R01 AR 46426-02
The first mammalian metapodial (MP1) has periodically been argued to actually be a phalanx, because the first ray has one less element than the four posterior rays, and because the MP1 growth plate is proximal like those of all phalanges, rather than distal as in metapodials 2–5. However, growth plates are formed at both ends in non-therian tetrapod metapodials, and phylogenetic analysis demonstrates that growth plate loss is a therian synapomorphy that postdates the establishment of the mammalian phalangeal formula. These data, along with results of developmental and morphological studies, suggest that the MP1 is not a phalanx. The singular, proximal growth plates in MPs 2–5 are likely to be an adaptation to dynamic erect quadrupedal gait which was characterized by conversion of the posterior metapodials into rigid struts with the carpus/tarsus. While the adaptive significance of the reversed ossification of MP1 is less clear, we present three functional/developmental hypotheses. J. Exp. Zool. (Mol. Dev. Evol.) 320B:276–285, 2013. © 2013 Wiley Periodicals, Inc.