Researchers in Japan have identified four fossil bones that had gone unnoticed for about 30 years inside rock containing mosasaur remains, according to ScienceDaily.
The bones were originally found between 1990 and 1992 in Sobura, Kaizuka City, Osaka Prefecture, and later stored at the Natural History Museum in Kishiwada City. When the team revisited pieces of the rock that had not yet been fully prepared, they found additional bones still embedded in the material.
One of the most important discoveries was a premaxilla, the bone at the front of the upper jaw. Scientists said this is the first confirmed premaxilla from a mosasaur fossil discovered in Japan.
Researchers also studied the basisphenoid, a bone near the braincase, and found traits that do not match those seen in previously described mosasaurs. Those differences suggest the fossil could represent a species new to science, though further research will be needed to confirm that.
The findings were presented at the 177th Annual Meeting of the Palaeontological Society of Japan, held at Osaka Metropolitan University on June 27, 2026.
