Megamouth enters the LRT

Figure 1. The Megachasma skull is made of cartilage and several jaw elements are fused together, as in other higher sharks.

Figure 1. The Megachasma skull is made of cartilage and several jaw elements are fused together, as in other higher sharks. A gill bar was added here (in red) based on the appearance of the animal in vivo (Fig. 2), which a reader (TG) kindly indicated is wrong! So ignore the added graphics. 

The megamouth shark
Megachasma (Figs. 1, 2), just entered the large reptile tree (LRT, 1648+ taxa; subset Fig. 3) between the primitive sharks Cladoselache (Late Devonian) + Chalmydoselache (extant) and all higher sharks + rays.

Figure 1. Megachasma in vivo. Note the single cusp teeth.

Figure 1. Megachasma in vivo. Note the single cusp teeth and short rostrum.

Megachasma pelagios (Taylor, Compagno and Struhsaker 1983; up to 5m) is the extant megamouth shark, a deep water filter feeder. In the LRT Megachasma nests between Cladoselache and higher sharks (Fig. 3). It is the basalmost shark with single cusp teeth. The rostrum extends only slightly over the mouth with anteriorly-oriented nares, as in more primitive taxa.

Figure 3. The addition of Megachasma to the LRT provides a transitional taxon between primitive sharks and derived sharks + rays.

Figure 3. The addition of Megachasma to the LRT provides a transitional taxon between primitive sharks and derived sharks + rays.

References
Taylor LR, Compagno LJV and Struhsake PJ 1983. Megamouth – a new species, genus, and family of lamnoid shark (Megachasma pelagios, family Megachasmidae) from the Hawaiian Islands. Proceedings of the California Academy of Sciences. 43 (8): 87–110.

wiki/Megachasma
wiki/Megamouth_shark

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