The nature of these four groups and their interrelationships remains unusual, according to researchers, and a large body of research is currently being conducted.
The latest mosasaur specimen discovered in Mexico this week has small teeth and a long, slender jaw and belongs to the genus Plioplatecarpinae.
The newly discovered fossils come from limestone blocks known to be rich in well-preserved traces of fish and marine reptiles, largely because the area was formed under oxygen-deficient conditions.