Hyperphalangy in a new sinemydid turtle from the Early Cretaceous Jehol Biota.

Shuai Shao,Chang-Fu Zhou,Lan Li,Yang Yang

doi:10.7717/peerj.5371

Abstract

Hyperphalangy is a rare condition in extant aquatic turtles, and mainly limited to soft-shelled turtles. Here we report a new freshwater turtle, Jeholochelys lingyuanensis gen. et sp. nov. from the Early Cretaceous Jehol Biota of western Liaoning, China. This new turtle is characterized by a hyperphalangy condition with one additional phalanx in pedal digit V, rather than the primitive condition (phalangeal formula: 2-3-3-3-3) of crown turtles. J. lingyuanensis is recovered with other coexisting turtles in the family Sinemydidae in the phylogenetic analysis. This discovery further confirms that hyperphalangy occurred multiple times in the early evolutionary history of the crown turtles. Hyperphalangy is possibly a homoplasy in Jeholochelys and the soft-shelled turtles to adapt to the aquatic environments.

Highlights

Extant turtles of terrestrial, semi-aquatic, and aquatic habitats have evolved diverse morphologic adaptations for these environments that involves the shell, limb proportions, and the phalangeal count (Joyce & Gauthier, 2004; Renous et al, 2008)
A new sinemydid turtle is described from the Early Cretaceous Jiufotang Formation of Sihedang, Lingyuan, western Liaoning, China. This turtle is characterized by a series of features including a phalangeal formula of 2-3-3-3-4 for the pes, as a contrast to the common condition of the 2-3-3-3-3 formula of crown turtles
Material The fossil specimens of the new taxon are recovered from the Early Cretaceous Jiufotang Formation of the Jehol Biota at a site (4054′46′′N; 11929′45′′E) near Liuligou, Sihedang Township, Lingyuan City, western Liaoning Province, China (Fig. 1)

Summary

INTRODUCTION

Semi-aquatic, and aquatic habitats have evolved diverse morphologic adaptations for these environments that involves the shell, limb proportions, and the phalangeal count (Joyce & Gauthier, 2004; Renous et al, 2008). Terrestrial turtles (e.g., testudinids) have relatively short manus and pedes with reduced phalangeal count (Crumly & Sánchez-Villagra, 2004; Joyce & Gauthier, 2004). Hyperphalangy in soft-shelled turtles does not contribute to the formation of longer flippers, the additional phalanges could help to enlarge the paddle surface to facilitate aquatic mobility (Delfino, Fritz & Sánchez-Villagra, 2010). A new sinemydid turtle is described from the Early Cretaceous Jiufotang Formation of Sihedang, Lingyuan, western Liaoning, China. This turtle is characterized by a series of features including a phalangeal formula of 2-3-3-3-4 for the pes, as a contrast to the common condition of the 2-3-3-3-3 formula of crown turtles. The new taxon shows hyperphalangy with one additional phalanx in pedal digit V provides an opportunity for investigating the evolution of hyperphalangy in turtles

MATERIALS AND METHODS

Findings

DISCUSSION