Skeletal Anatomy of the Bigeye Sand Tiger Shark, Odontaspis noronhai (Lamniformes: Odontaspididae), and Its Implications for Lamniform Phylogeny, Taxonomy, and Conservation Biology

Abstract

Lamniformes (Chondrichthyes: Elasmobranchii) is a group of sharks that consists of 15 extant species with a wide range of morphological diversity. The most rarely captured lamniform is Odontaspis noronhai, and many aspects of its biology remain unknown to date. In this study, the skeletal anatomy of a previously described specimen of O. noronhai was examined using computed tomography. The new skeletal data were then added to a previously published morphology-based character matrix to conduct a new phylogenetic analysis of the Lamniformes. Our phylogenetic study strongly suggests non-monophyly of Odontaspididae, that traditionally consisted of Carcharias taurus, O. ferox, and O. noronhai. Thus, the family Carchariidae is formally resurrected for the genus Carcharias to separate it from the family Odontaspididae sensu stricto for Odontaspis. The overall topology of our phylogenetic trees is similar to that of previously published morphology-based trees and drastically different from the tree topology generally attained by molecular data that cluster Alopias, Megachasma, Odontaspis, and Pseudocarcharias together as a separate clade. The major topological discrepancy between molecular and morphological trees may be attributed to unconventionally asynchronous rates between morphological and molecular evolution, at least in certain species within the Lamniformes, along with likely manifestation of mosaic evolution. The recognition of the family Carchariidae is important to conservation biology, because the extinction of C. taurus would not only mean the elimination of the genus Carcharias, but also the entire family Carchariidae. Our study demonstrates the importance of the integration of both morphological and molecular information to understand organismal evolution.