Genus: Hydrargysaurus WICK & SHILLER II, 2020
Etymology: Greek, hydrargyros, "water silver" in reference to the many abandoned mercury mines near the type loclaity, and Greek, sauros, "lizard."

Species: gladius WICK & SHILLER II, 2020
Etymology: Latin, gladius, "sword." In reference to the resemblance of blade of an ancietn roman sword.

Holotype: TMM 45947-533

Locality: Lowerverse site (TMM 45947), approximately 15 km north of Terlingua, private land just west of Big Bend National Park, Brewster County, Texas.

Horizon: Middle of the lower Shale Member, Aguja Formation.

Biostratigraphy:

Age: Early Campanian Stage, Senonian Subepoch, Gulf Epoch, Late Cretaceous.

Material: Meidal left dentary fragment with teeth.

Referred material:

TMM 4597-534, 535, 536: Dentary and premaxillary fragments with teeth.