Developmental basis of limb homology in Pleurodiran turtles and the identity of the hooked element in the chelonian tarsus

M. FABREZI, A. MANZANO, V. ABDALA AND H. ZAHER

ZOOLOGICAL JOURNAL OF THE LINNEAN SOCIETY

Blackwell Publishing

Lugar: London; Año: 2009 vol. 155 p. 845 - 866

0024-4082

 Although Pleurodiran represent an important component of extant turtle radiation, our knowledge of development and homology of limb bones in turtles rests mostly upon observations made on derived members of the Cryptodiran clade. Herein, we describe limb development in three pleurodirans: Podocnemis unifilis, P. sextuberculata and Phrynops hilarii, as an effort to contribute in filling this anatomical gap. At earlier stages of limb development, we described the Y-shaped condensation that gives rise to the zeugopodial cartilages, and differentiation of the primary axis/digital arch that reveals the invariant pattern common to tetrapods. There are up to four central cartilaginous foci in the carpus, and the proximal tarsale is formed by the fusion of the fibulare, intermedium and Centrale 4. Digital development is similar for the five digits. Changes in Toe V occur predominantly in the Distal Tarsale 5.Ontogenetic reduction of phalanxes is observed in Toe V of Podocnemis. Based on these results, we suggest that the hooked element present in the chelonian tarsus, and traditionally recognized as a modified fifth metatarsale, is actually the fifth distal tarsale. Additionally, our data on limb development of pleurodiran turtles supply more taxonomically comprehensive information to interpret limb configuration within the chelonian clade.