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.
Paleontologists have differing opinions on the classification of this group: some consider it a distinct evolutionary branch, while others see it as an intermediate stage within the basal mosasauroids. However, recent molecular and morphological studies indicate that they are the earliest known members of the lineage leading to modern mosasaurs.