"Tylosaurus" was one of the largest mosasaurs of all time. The largest known specimen, a skeleton of "T. proriger" from the University of Kansas Natural History Museum nicknamed "Bunker" (KUVP 5033), has been estimated to measure between long. Some isolated fragments have been estimated to belong to individuals measuring or more. The genus exhibits Cope's rule, in which its body size has been observed to generally increase over geologic time. In North America, the earliest representatives of "Tylosaurus" during the Turonian and Coniacian (90-86 mya), which included early "T. nepaeolicus" and its precursors, typically measured long and weighed between . During the Santonian (86-83 mya), "T. nepaeolicus" and newly-appearing "T. proriger" were long and weighed around . By the Early Campanian, "T. proriger" attained lengths of .