ABSTRACT
Chondrichthyan shes (sharks, rays, and ratshes) comprise one of only two surviving lineages of jawed vertebrates, or gnathostomes (Carroll, 1988). Their sister group, Osteichthyes, includes ray-nned shes and tetrapods and encompasses the vast majority of vertebrate species. Despite the important outgroup perspective that chondrichthyans lend to higher level studies of osteichthyans, little attention has yet been paid to chondrichthyan interrelationships; that is, although these shes are employed as proxies for ancestral jawed vertebrates, there is no well-supported framework for interpreting the polarity of character state changes within the group. This is particularly the case for skates, rays, and their allies (Batoidea, hereafter “batoids”), which comprise the majority of chondrichthyan species diversity (≈630 of ≈1170 species) and morphological disparity, including departures from a shark-like ancestral body
plan (Compagno, 1999, 2005). The spectrum of batoid body plans rivals that of many other vertebrate groups and includes such disparate forms as sawshes with elongate rostral saws, 7-meter-wide planktivorous mantas, and benthic, saucer-shaped torpedo rays capable of generating powerful electric discharges from modied branchial muscles (Davy, 1829; Stiassny et al., 2004).
