Patterns of carpal development among anuran amphibians

The unity and diversity of developmental processes in the vertebrate limb h ave singular importance in the interpretation of evolutionary hypotheses of tetrapod diversification. In anurans, the intraordinal diversity of foreli mbs seems to be related to the fusion of distal carpals, whereas proximal c arpals are invariable. However, there are different ontogenetic pathways in volved in the differentiation of proximal carpals. This study presents a co mparative analysis of early developmental features in one archeobatrachian and 23 neobatrachian species representing five families and explores the va riability in the differentiation of carpal cartilages. We found new evidenc e supporting the presence of an embryonic intermedium that incorporates wit h the ulnare. Difference between the pipid Xenopus and the neobatrachians i s interpreted as a change in the rate of differentiation of Distal Carpal 5 that does not affect the developmental pattern of digits. The developmenta l variability exhibited by the intermedium, radiale, and Element Y is combi ned in patterns that converge on the same adult carpal morphology among neo batrachians; these patterns appear to contain potentially useful phylogenet ic information. J. Morphol. 249:210-220, 2001. (C) 2001 Wiley-Liss. Inc.