to the subfamily Mosasaurinae. The skull of Russelosaurus shows many characters diagnostic of the Plioplatecarpinae while retaining many plesiomorphic traits. Cladistic analysis indicates a close relationship between Russellosaurus and Yaguarasaurus columbianus, a primitive South American mosasaur from the Turonian of Colombia. Together with Tethysaurus nopcsai, another early mosasauroid from the Turonian of Morocco, these genera are believed to constitute a clade "basal to the divergence" of the subfamilies Plioplatecarpinae and Tylosaurinae. Based on the lack of fusion between elements of the basicarnium and a high degree of vascularization of the bone surface, which suggests the animal was undergoing a rapid growth stage when it died, the holotype skull of Russellosaurus coheni is believed to have come from a subadult individual. An even more primitive mosasaur, Dallasaurus turneri, was recovered from the same Cedar Hill locality as this specimen. References Sources Bell, G. L. Jr., 1997. A phylogenetic revision of North American and Adriatic Mosasauroidea. pp. 293–332 In Callaway J. M. and E. L Nicholls, (eds.), Ancient Marine Reptiles. Academic Press, 501 pp. Polcyn, M. J. and Bell, G. L., Jr. 2005. Russellosaurus coheni n. gen., n. sp., a 92 million-year-old mosasaur from Texas (USA), and the definition of the parafamily Russellosaurina. Netherlands Journal of Geosciences 84(3):321–333. Wright, K. R. and S. W. Shannon. 1988. Selmasaurus russelli, a new plioplatecarpine mosasaur (Squamata, Mosasauridae) from Alabama. Journal of Vertebrate Paleontology 8(1):102–107. Russellosaurins Mosasaurs of North America Fossil taxa described in 2005