A new freshwater lonchidiid hybodontiform shark (Chondrichthyes, Elasmobranchii) from the Upper Triassic Momonoki Formation in Yamaguchi, Japan

Abstract

ABSTRACT We describe an assemblage of isolated hybodontiform shark teeth from the nonmarine Upper Triassic (Carnian) Momonoki Formation in the town of Ominecho in Mine, Yamaguchi, Japan. These teeth were first reported in 1996 and tentatively referred to the genus Hybodus, but their taxonomy was not rigorously evaluated in an apomorphy-based context, and they have since been mostly overlooked. Herein, we assign them to a new species, Parvodus ominechonensis, based on a combination of synapomorphies of the lonchidiid genus Parvodus and autapomorphic character states. A diversity of Triassic hybodontiforms is known from Japan, but of these, Parvodus ominechonensis sp. nov. is the only taxon known from nonmarine deposits and the first reported occurrence of Lonchidiidae. Parvodus ominechonensis fills a gap in the stratigraphic record of Parvodus between occurrences in Middle Triassic (Anisian) and Middle Jurassic (Bajocian) strata. The global Triassic record of Parvodus comprises Parvodus huizodus from the Olenekian of China, Parvodus sp. from the Anisian of China, and Parvodus ominechonensis from the Carnian of Japan, of which Parvodus ominechonensis and Parvodus huizodus are known from nonmarine deposits. After the Triassic, Parvodus is known from marine and nonmarine strata across Laurasia and in South America until its extinction during the Early Cretaceous. This suggests that Parvodus may have originated in freshwater habitats in the South China region of Pangea following the end-Permian mass extinction and diversified throughout the Triassic in present day East Asia before attaining a global distribution later in the Mesozoic. http://zoobank.org/urn:lsid:zoobank.org:pub:42B4D1C1-F4BE-4296-896B-01B048BDE25F