A new fossil megamouth shark (Lamniformes, Megachasmidae) from the Oligocene-Miocene of the western United States

<div><p>ABSTRACT</p><p>The extant megamouth shark, <i>Megachasma pelagios</i> (Lamniformes: Megachasmidae), is a large filter-feeding fish. We here describe a new species of <i>Megachasma</i>, <i>M. applegatei</i>, sp. nov., a putative sister species of the extant <i>M. pelagios</i>, based on isolated teeth from late Oligocene–early Miocene (late Chattian–Aquitanian) marine deposits in California and Oregon, U.S.A. Although showing a megachasmid tooth design, teeth of <i>M. applegatei</i>, sp. nov., exhibit a wide morphological range and are reminiscent to those of odontaspidid sharks with strong heterodonty. <i>Megachasma applegatei</i>, 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 <i>M. applegatei</i>, sp. nov., was broadly adapted to a wide bathymetric tolerance or was a nektopelagic feeder over both deep and shallow water habitats.</p> <p>SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at <a href="http://www.tandfonline.com/UJVP" target="_blank">http://www.tandfonline.com/UJVP</a>.</p> </div

A new clade of putative plankton-feeding sharks from the Upper Cretaceous of Russia and the United States

<div><p>ABSTRACT</p><p><i>Eorhincodon casei</i> from Russia and <i>Megachasma comanchensis</i> from the United States are two Cretaceous taxa initially described as putative planktivorous elasmobranchs, but the type specimens of these two taxa were subsequently reinterpreted to represent taphonomically abraded teeth of an odontaspidid, <i>Johnlongia</i> Siverson (Lamniformes: Odontaspididae). Here, we redescribe the type materials of ‘<i>E. casei</i>’ and ‘<i>M. comanchensis</i>’ and describe additional specimens of these species from other Late Cretaceous localities in Russia and the United States. These specimens demonstrate that (1) the two fossil taxa are valid species; (2) they warrant the establishment of a new genus of presumed planktivorous sharks, <i>Pseudomegachasma</i>, gen. nov., to accommodate the two species; and (3) the new genus is sister to <i>Johnlongia</i> and together constitute a new subfamily Johnlonginae, subfam. nov., tentatively placed in the family Odontaspididae sensu stricto. This taxonomic placement indicates that the putative planktivorous clade was derived from a presumed piscivorous form (<i>Johnlongia</i>), with an implication that <i>Pseudomegachasma</i>, gen. nov., evolved a plankton-eating habit independent of the four known planktivorous elasmobranch clades (Rhincodontidae, Megachasmidae, Cetorhinidae, and Mobulidae). It also indicates that planktivorous diets evolved independently at least three times in the order Lamniformes (i.e., Megachasmidae, Cetorhinidae, and Odontaspididae), and more significantly, <i>Pseudomegachasma</i>, gen. nov., would represent the oldest known plankton-feeding elasmobranch in the fossil record. The present fossil record suggests that <i>Pseudomegachasma</i>, gen. nov., evolved in a relatively shallow-water environment in Russia in the early Cenomanian or earlier and subsequently migrated to the North American Western Interior Seaway by the mid-Cenomanian.</p><p>http://zoobank.org/urn:lsid:zoobank.org:pub:D5D0400FD438-4A95-8301-DD47991572F6</p><p>SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP</p></div