Regarded by some paleontologists as a distinct monophyletic group and by others as an adaptive grade within the basal mosasauroids, recent molecular and morphological data suggests that they are the oldest known members of the lineage leading to the mosasaurs.
The classification of this group is debated among paleontologists, with some seeing them as a distinct evolutionary branch and others viewing them as an intermediate stage within the basal mosasauroids. However, recent molecular and morphological studies suggest they are the earliest known members of the lineage leading to modern mosasaurs.