Newly discovered fossil of hybodontiform shark found in Japan

Japanese paleontologists have described a new species of shark-like cartilaginous fish based on fossil teeth found in the Momonoki Formation of the Late Triassic Period.

Named Parvodus ominechonensis The newly identified shark species lived during the Late Triassic period, between 237 million and 227 million years ago.

it is Parvodas Small extinct genus Hybodontiform Shark It has been known since the Mesozoic era.

“Hybodontiforme is an extinct lineage of sharks that is generally considered to be the sister lineage of Neoselachia (i.e. rays, rays, and modern sharks) within the chondrichthyes Euselaciidae,” he said. Dr. Benjamin T. Breedon III Researchers from the National Museum of Nature and Science in Tsukuba and his colleagues.

“The oldest clearly hybodontiform fossils are from the Mississippian, but the discovery of isolated teeth has pushed the oldest record of this group back to the Late Devonian.”

“Hybodontiform fossils have been found primarily in coastal and lagoonal deposits throughout the Late Palaeozoic, suggesting a shallow-marine palaeoecology of the clade's ancestors.”

“However, some hybodontiforms appear to have become euryhaline early in the evolution of their lineage, and since the Mississippian, hybodontiforms have repeatedly invaded freshwater environments.”

“Hybodontis were the most abundant group of sharks among marine and non-marine vertebrate groups throughout the Early Mesozoic, but their diversity declined after the Early Jurassic until their extinction at or near the end of the Cretaceous.”

Ecological reconstruction of the hybodontiform shark Strophodus rebeccae Image credit: Jorge Blanco / CC BY 4.0.

Some isolated teeth Parvodus ominechonensis It was collected from the non-marine peach tree layer in Ominecho (romanized as Ominecho) in the western part of Mine City, Yamaguchi Prefecture.

“The diversity of Triassic hybodontids is known from Japan, among which Parvodus ominechonensis It is the only species known from non-marine sediments and the first reported occurrence of this family. Ronchididae” the paleontologist said.

According to the study: Parvodus ominechonensis Filling in gaps in the geological record Parvodas Between occurrences in Middle Triassic and Middle Jurassic strata.

“The Triassic Global Record Parvodas include Parvodus physodus From the Chinese Olenekians, Parvodas Chinese Anisian sp., and Parvodus ominechonensis The Carnian period in the Japanese Archipelago Parvodus ominechonensis and Parvodus physodus “It is also known from non-marine deposits,” the authors say.

“Since the Triassic Period, Parvodas It is known to have lived in marine and non-marine strata throughout Laurasia and South America until its extinction in the Early Cretaceous.

“this is, Parvodas They may have originated in freshwater habitats in the southern Chinese region of Pangaea after the end-Permian mass extinction, diversified throughout the Triassic in what is now East Asia, and achieved a global distribution during the late Mesozoic.”

Discovery Parvodus ominechonensis It has been reported paper In Journal of Vertebrate Paleontology.

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Benjamin T. Breedon III others2023. A new species of hybodontiform shark (Chondrichthyes, Elasmobranchia), a freshwater shark from the Upper Triassic Momonoki Formation of Yamaguchi Prefecture. Journal of Vertebrate Paleontology 43(5); doi:10.1080/02724634.2024.2322749