Tylosaurus
Tylosaurus (from the ancient Greek τυλος (tylos) 'protuberance, knob' + Greek σαυρος (sauros) 'lizard') is a genus of mosasaur, a large, predatory marine reptile closely related to modern monitor lizards and to snakes, from the Late Cretaceous.
A distinguishing characteristic of Tylosaurus is the elongated conical rostrum that protrudes from its snout, from which the genus is named. Unlike typical mosasaurs, Tylosaurus did not have teeth up to the end of the snout nor on the bony protuberance that is the rostrum, and scientists believe that this feature was primarily used for combative purposes such as ramming.[8][9][10] This is supported with a uniquely broad and somewhat rectangular internarial bar (the extension of the premaxilla on the top of the skull that held together the nasal and upper jaws) that provided high cranial stability and resistance to stress forces.[9] In addition, the development of the elongated rostrum in infant Tylosaurus rules out the alternative explanation that it was developed as a function of sexual behavior.[10] Tylosaurus also had 24 to 26 teeth in the upper jaw, 20 to 22 teeth on the palate, 26 teeth on the lower jaw, 29 to 30 vertebrate between the skull and hip, 6 to 7 vertebrae in the hip, 33 to 34 vertebrae in the tail with chevrons, and a further 56 to 58 vertebrae making up the tip of the tail.[11]
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 previously been estimated to measure between 12–15.8 meters (39–52 ft) long,[12][13] but based on the fact that the material comes from the Early Campanian, it is more likely that the specimen (and T. proriger in general) attained maximum lengths of 13–14 meters (43–46 ft).[14][15] Some isolated fragments have been estimated to belong to individuals measuring 14 meters (46 ft) or more.[16] The genus exhibits Cope's rule, in which its body size has been observed to generally increase over geologic time.[12] In North America, the earliest representatives of Tylosaurus during the Turonian[17] and Coniacian (90-86 mya), which included early T. nepaeolicus and its precursors, typically measured 5–7 meters (16–23 ft) long[12] and weighed between 200–500 kilograms (440–1,100 lb).[18] During the Santonian (86-83 mya), T. nepaeolicus and newly-appearing T. proriger were 8–9 meters (26–30 ft) long[12] and weighed around 1,100 kilograms (2,400 lb).[19]
Commenting on the maximum sizes of large mosasaurs, paleontologist Mike Everhart, a leading expert on mosasaurs, speculated that it would be possible for some extremely old Tylosaurus individuals to reach 20 meters (66 ft) in absolute maximum length. However, this is with awareness that there is no fossil evidence suggesting such sizes and that the odds of preserving such a rare individual are "far too great."[20]
In 2014, the Guinness World Records awarded the Canadian Fossil Discovery Centre a record for "Largest mosasaur on display," specifically, a 13.05 m (42.8 ft) long skeleton of T. pembinensis nicknamed "Bruce."[21] However, the skeleton was assembled for display prior to a 2010 reassessment of the species that found its original number of vertebrae to be exaggerated, implying that the actual size of the animal was likely smaller.[22][23]
