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

ABSTRACTThe 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 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. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at http://www.tandfonline.com/UJVP.

摘要
现生巨口鲨（Megachasma pelagios，鼠鲨目：巨口鲨科）是一种大型滤食性鱼类。本文基于美国加利福尼亚州与俄勒冈州晚渐新世-早中新世（晚恰特期-早阿基坦期）海相地层中分离出的孤立牙齿，描述了巨口鲨属一新种——阿普尔盖特巨口鲨（Megachasma applegatei, sp. nov.），该种被推测为现生巨口鲨（M. pelagios）的姊妹群物种。尽管阿普尔盖特巨口鲨（M. applegatei, sp. nov.）的牙齿仍保留巨口鲨科的牙齿构型，但其展现出宽泛的形态变异范围，且与具有显著异型齿特征的锥齿鲨科（Odontaspididae）鲨鱼牙齿极为相似。阿普尔盖特巨口鲨（M. applegatei, sp. nov.）的总长度通常约为6米，食性范围较广，可能涵盖小型鱼类与浮游无脊椎动物。化石记录表明，阿普尔盖特巨口鲨（M. applegatei, sp. nov.）要么具备宽泛的水深适应耐受能力，要么是一种可在深浅水栖息环境中活动的自游浮游性摄食者。
补充数据——本文的补充材料可通过http://www.tandfonline.com/UJVP免费获取。