New Mosasaur Fossils Discovered in Osaka, Japan
Researchers from Okayama University of Science, Tokyo City University, and the Natural History Museum in Kishiwada City, Osaka Prefecture, have identified four fossil bones that remained unrecognized for nearly 30 years. The bones were found within rock associated with mosasaur remains collected in Kishiwada City.
Among the newly identified fossils is the premaxilla, situated at the front of the upper jaw. This discovery marks the first confirmation of a premaxilla in a mosasaur fossil from Japan. Other distinctive anatomical features in the bones do not align with characteristics seen in previously described mosasaurs, indicating a potential new species.
History of the Fossils
The fossils were initially uncovered between 1990 and 1992 in Sobura, Kaizuka City, Osaka Prefecture, and were subsequently preserved at the Natural History Museum in Kishiwada City. Researchers recently revisited these specimens, finding four fossil bones still embedded in the surrounding rock.
The premaxilla stands out as one of the most significant findings, being the first confirmed example of this bone in a Japanese mosasaur. At the time of the original discovery, researchers had a limited number of mosasaur specimens for comparison, complicating the identification process. Advances in anatomical research and comparative fossils in the intervening decades enabled the team to pinpoint the bone as a premaxilla.
Potential New Species
In examining the basisphenoid, a bone near the braincase, the researchers identified several unique characteristics. The bone features short horn-like projections and does not have a ventral median groove, distinguishing it from known mosasaurs. This combination of traits raises the possibility that it may represent an undescribed species.
The findings also highlight the value of examining unprepared specimens kept in museums and research collections. Fossils that have been stored for extended periods may still harbor undiscovered important bones or evidence that was overlooked during their initial collection.
This discovery could also enhance scientists’ understanding of marine ecosystems in the northwestern Pacific during the Cretaceous Period. Additional studies will be necessary to confirm whether the specimen indeed represents a new mosasaur species.
Presentation of Findings
The research team presented their results at the 177th Annual Meeting of the Palaeontological Society of Japan, which was held at Osaka Metropolitan University on June 27, 2026. The team comprised various experts, including master’s students and professors from multiple universities alongside curators from the Natural History Museum.
