Mosasauroidea

Mosasauroidea is a superfamily of extinct marine reptiles that existed during the Late Cretaceous. Basal members of this group consist of small semiaquatic forms with terrestrial limbs ("plesiopedal"), while later members include larger fully aquatic paddle-limbed ("hydropedal") forms commonly known as mosasaurs. These were traditionally grouped within their own separate families, the Aigialosauridae and Mosasauridae respectively. However, phylogenetic studies have since found plesiopedal mosasauroids to be a non-monophyletic group, with some taxa nestled within the mosasaurids. Daniel Madzia

Vallecillosaurus is an extinct genus of mosasauroid from the Late Cretaceous period, that lived in Mexico, in the state of Nuevo León. It was a relatively small reptile measuring less than long.