Vertebrata - Sauropterygia - Polycotylidae

Synonyms: Ceraunosaurus brownorum Thurmond 1968, Dolichorhynchops willistoni Riggs 1944, Trinacromerum anonymum Williston 1903, Trinacromerum brownorum Thurmond 1968, Trinacromerum willistoni Riggs 1944

Belongs to Trinacromerum according to L. B. Albright et al. 2007

Sister taxa: Trinacromerum kirki, Trinacromerum lafquenianum

Type specimens:

• Trinacromerum bentonianum: USNM 10945. Its type locality is near Downs (USNM), which is in a Turonian marine limestone in the Carlile Shale Formation of Kansas.
• Ceraunosaurus brownorum: SM 3025, a skeleton (nearly complete skeleton). Its type locality is Lake Waco Dam, which is in a Cenomanian marine shale in the Lake Waco Formation of Texas.
• Trinacromerum anonymum: Its type locality is near Paradise Creek (KUVP), which is in a Turonian marine horizon in the Carlile Shale Formation of Kansas.
• Trinacromerum willistoni: KUVP 5070, a partial skeleton (Skull, 50 vertebrae, and most of the girdles). Its type locality is U.S. highway 81 roadcut, south of Concordia (FHSM 1331, T. willistoni type), which is in a Cenomanian marine horizon in the Greenhorn Limestone Formation of Kansas.

Ecology: aquatic carnivore