Evolution of the odontophore and the origin of the neoasteroids

A small internal odontophore, positioned interradially between the inner surfaces of the paired oral ossicles, and separated from the inferomarginals by actinal ossicles is one of the defining characters of the post-Palaeozoic Neoasteroidea (Gale, 1987; 2011). Plesiomorphically, as in Paxillosida, the odontophore has a small external face. In Palaeozoic asteroids the homologue of the odontophore, sometimes called the axillary or axillary inferomarginal, is often a large ossicle, which proximally articulates with the interior of the paired oral ossicles, and distally with the two most proximal inferomarginals (e.g. Calliasterella Gale, 2011). This condition obtains also in the Permian Monaster canarvonensis Kesling, 1969 (Fig. 1E). In Permaster grandis Kesling, 1969, the external surface of the odontophore is reduced, but the plate remains in firm articulation with the first pair of inferomarginals (Fig. 1F).