[2] Like the closely related tethysaurines, all yaguarasaurines were plesiopedal (meaning primitive and not as well adapted to marine life as later mosasaurs).

They generally retained relatively small sizes compared to later giant mosasaurs, though Yaguarasaurus itself might have grown rather large.

They had a plesiopedal limb condition, meaning that they were not as well adapted to marine life as later mosasaurs and probably kept to shallow bodies of water.

Palci et al. (2013)[2] diagnosed the Yaguarasaurinae as the most recent common ancestor of Russellosaurus, Romeosaurus, and Yaguarasaurus, and all of its descendants.

Unambiguous character states were listed as follows: "frontals not invaded by posterior end of nares (i.e., lack of distinct narial emargination on frontals); jugal rami form a 90◦ angle and produce a distinct posteroventral process at their junction; quadrate ala forms a shallow concavity; medial parapet of dentary (dentary medial shelf) low, tooth roots largely exposed in medial view; dentary has a projection anterior to the first tooth (reversed in Russellosaurus)".