ABSTRACT—The extant megamouth shark, Megachasma pelagios (Lamniformes: Megachasmidae), is a large filter-feeding
fish. We here describe a new species of Megachasma, M. applegatei, sp. nov., a putative sister species of the extant M. pelagios,
based on isolated teeth from late Oligocene–early Miocene (late Chattian–Aquitanian) marine deposits in California and
Oregon, U.S.A. Although showing a ... [Show full abstract] megachasmid tooth design, teeth of M. applegatei, sp. nov., exhibit a wide morphological
range and are reminiscent to those of odontaspidid sharks with strong heterodonty. Megachasma applegatei, sp. nov., could
have commonly measured approximately 6 m in total length and likely had a wide range of diet, possibly including small fishes
and planktonic invertebrates. The fossil record indicates that either M. applegatei, sp. nov., was broadly adapted to a wide
bathymetric tolerance or was a nektopelagic feeder over both deep and shallow water habitats.