Comparative anatomy of the superfamily Myliobatoidea (Chondrichthyes) with some comments on phylogeny.

The anatomy of species belonging to the superfamily Myliobatoidea was examined with the aim of better determining their phylogenetic relationships. A wide variation among genera was observed in skeletal anatomy, despite the fact that they all share a common morphological pattern. However, variation among species of the same genus was low, excepting Mobula. Dorsal musculature showed a substantial consistency, except for the epiaxialis muscle, which was larger in rhinopterids and mobulids. Variation in the ventral muscles was low among species of the same genus, but considerable among different genera. Mobulids have a reduction in ventral muscles, while rhinopterids and myliobatoids show an increase in muscular mass. A consensus tree shows a basal split into two groups. The first includes the family Gymnuridae with the genera Gymnura and Aetoplatea; this group is supported by seven synapomorphies, including: 27(1) ceratobranchialis fused proximally, 36(1) anterior lateral processes present in the synarcual, 52(0) quadratomandibularis internal muscle present. The second group is composed of the family Myliobatidae (Myliobatis, Aetomylaeus, Aetobatus, Rhinoptera, Mobula, and Manta), this group is supported by 11 synapomorphies, including: 5(1) first postorbital process fused with the second, 21(1) fused mandibular symphysis, 24(1) first hypobranchial cartilage absent, 48(2) epiaxialis muscle inserted in the cranial orbital region, 73(1) pectoral fins joined behind the orbital region. This study concluded that myliobatoids (Myliobatis, Aetomylaeus, and Aetobatus) integrate a monophyletic group which, unlike other phylogenies previously obtained, is the sister group of rhinopterids (Rhinoptera). Mobulids (Mobula and Manta) are the sister group of myliobatoids-rhinopterids. 2004 Wiley-Liss, Inc.