30-Year-Old Japanese Mosasaur Fossils Yield First Premaxilla and Possible New Species Traits

Researchers at Okayama University of Science and partner institutions returned to matrix stored at the Natural History Museum, Kishiwada City, and extracted four additional bones. The premaxilla, previously undocumented in Japanese material, was identified through expanded comparative collections unavailable in the early 1990s. The basisphenoid displays short lateral projections and lacks a ventral median groove, a combination not recorded in any described mosasaur. The fossils originate from Late Cretaceous marine deposits in Osaka Prefecture and were first collected when fewer than a dozen well-preserved mosasaur skulls existed for reference. Three decades of global discoveries now allow these anatomical distinctions to be recognized. The work was reported at the 177th Annual Meeting of the Palaeontological Society of Japan. Museum re-preparation of long-stored specimens is proving disproportionately valuable for marine reptile systematics. The northwestern Pacific record remains sparse; a new local taxon would refine biogeographic models of mosasaur dispersal before the end-Cretaceous extinction. Additional mechanical preparation and CT scanning are required before formal taxonomic assessment. Next steps include phylogenetic analysis once the remaining matrix is removed and comparison with recently described Pacific mosasaurs. If diagnostic characters hold, formal description as a new species could occur within two years.