Tethysaurinae

[2] A possible member of this clade (subfamily) is a mosasaur specimen known from a maxilla fragment, found in 1960 in the Czech Republic (then Czechoslovakia), in Dolní Újezd near Litomyšl.

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

[4] Makádi et al. (2012)[4] originally diagnosed the Tethysaurinae as all mosasaurs descended from the recentmost common ancestor of Tethysaurus nopscai and Russellosaurus coheni.

Unambiguous character states were listed as follows: "predental rostrum absent; premaxilla-maxilla suture ends anterior to or level with the midline of the fourth maxillary tooth; nearly straight frontoparietal suture; quadrate alar concavity shallow; elongated stapedial pit (at least three times longer than wide); quadrate distal condyle saddle-shaped, upward deflection of quadrate distal condyle absent; mandibular glenoid formed mainly by articular; cervical synapophyses extend below ventral border of centrum; dorsoventrally compressed centra in precaudal vertebrae; two sacrals with large ribs/transverse processes subcircular/oval in cross-section; facet for ilium on tip of sacral transverse processes; very elongated (two times longer than wide) pontosaur-like caudal centra; anteroposteriorly narrow scapula; ilium with posterior iliac process with compressed dorsal end bearing longitudinal grooves and ridges, and spoon-shaped preacetabular process overlapping the pubis".

The original definition of the Tethysaurinae was as all mosasaurs descended from the recentmost common ancestor of Tethysaurus nopscai and Russellosaurus coheni.

The known skeletal remains and a skeletal restoration of Pannoniasaurus .