The Tethysaurinae are a subfamily of mosasaurs, a diverse group of Late Cretaceous marine squamates. Members of the subfamily are informally and collectively known as "tethysaurines" and have been recovered from North America and Africa. Only two tethysaurine genera are known, Pannoniasaurus and Tethysaurus. The genera Yaguarasaurus and Russellosaurus were previously considered tethysaurines until they were grouped with Romeosaurus in the new subfamily Yaguarasaurinae. 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.