Simplification of the enameloid microstructure of large stingrays (Chondrichthyes: Myliobatiformes): a functional approach

Abstract

The microstructure of neoselachian teeth is characterized by a triple-layered enameloid, despite its purported absence in batoids since their appearance during the early Jurassic. This feature is thought to have been secondarily lost, as an adaptation to durophagy in batoids. The monophyletic Myliobatiformes are an ecologically diverse clade of batoids that includes very specialized taxa such as the filter-feeding mobulids and the durophagous myliobatids. Their diversity and recent evolutionary history (Palaeogene) make them an ideal model for assessing adaptive constraints that influence enameloid microstructure. This first study focusing only on batoid enameloid shows a very reduced single-layered enameloid in the derived filter feeders. However, most other taxa show a double-layered enameloid, which is probably plesiomorphic for batoids. It is concluded that the triple-layered enameloid is not a synapomorphy of the neoselachii as a whole, but of Selachimorpha only, and that diet specialization in derived myliobatoids indeeds impact their enameloid microctructure, which is confirmed by their fossil diversity. © 2013 The Linnean Society of London