The Carpus of Land Tortoises (Testudininae)

Abstract

This study of the manus of 30 species of living and fossil tortoises shows their structure to be considerably more variable than formerly presumed. The carpal pattern of each of the species studied is described and most are illustrated diagrammatically. Certain basic structural patterns reflect both the phyletic relationships of these species and the kinetics of the foot and stresses placed on it during locomotion. The carpal architecture of tortoises is easily derived from that of a generalized amphibian or a primitive reptilian arrangement. Some species of tortoises possess a distinct proximal centrale, here reported for the first time in any reptile. Other dissimilarities between the carpus of the tortoises and those of other reptiles are probably due to simple loss and/or fusion of elements, fusion being apparently much more common than loss in tortoises. The probable homologies of tortoise carpal elements are discussed. Trends in morphological and functional evolution of the carpus are: (1) subradial and subulnar lateral migration of elements, (2) fusion of proximal subradial and subulnar elements, and (3) fusion of distal carpal elements.