It had protective bony rings surrounding its eye sockets, indicating it lived in deep water. Its teeth are similar to those of some Triassic placodonts, so it may have lived a similar lifestyle, feeding on shellfish, large fish, and sea turtles.
A very large specimen found in Israel was for some time referred to as Oronosaurus, but is now regarded as a species of Prognathodon, P. currii. The recent discovery of 2 nearly complete fossils (one which included flippers) in Alberta, Canada have given scientists new data as previous fossils only contained the remains of the skull. One fossil included stomach contents, consisting of elements pertaining to a sea turtle, tarpon-size and trout-size fishes, and a possible cephalopod.
A new fossil found in 2008 and described in 2013 belonging to a 1.8 m juvenile Prognathodon was found in Jordan's Harrana Site. The fossil was remarkable in that it preserved the outline of the mosasaur's tail fins, revealing that Prognathodon, like Platecarpus and later mosasaurs also had a bilobed tail fluke resembling a downturned shark's tail, the shape of which may have aided the creature in surfacing, as well as attacking prey. The discovery also lends evidence to the theory that later mosasaurs were even more well-adapted to the lifestyle first occupied by the ichthyosaurs.
^Konishi, T., D. Brinkman, J. A. Massare, and M. W. Caldwell. 2011. New exceptional specimens of Prognathodon overtoni (Squamata, Mosasauridae) from the upper Campanian of Alberta, Canada, and the systematics and ecology of the genus.
^Lindgren, J.; Kaddumi, H. F.; Polcyn, M. J. (2013). "Soft tissue preservation in a fossil marine lizard with a bilobed tail fin". Nature Communications4. doi:10.1038/ncomms3423.
^Aaron R. H. Leblanc, Michael W. Caldwell and Nathalie Bardet (2012). "A new mosasaurine from the Maastrichtian (Upper Cretaceous) phosphates of Morocco and its implications for mosasaurine systematics". Journal of Vertebrate Paleontology32 (1): 82–104. doi:10.1080/02724634.2012.624145.
^Strganac, C., Jacobs L., Polcyn M., Mateus O., Myers T., Araújo R., Fergunson K. M., Gonçalves A. O., Morais M. L., Schulp A. S., da Tavares T. S., & Salminen J. (2014). Geological Setting and Paleoecology of the Upper Cretaceous Bench 19 Marine Vertebrate Bonebed at Bentiaba, Angola. Netherlands Journal of Geosciences. 1-16.