Copyright 1997-2009 by Mike Everhart


(ABOVE) A closer view of the mid-portion of the left side of the skull, showing the location of the sclerotic ring. The narrow finger of bone projecting forward over the sclerotic ring is the anterior extension of the postorbitalfrontal (POF). This is one of the key characteristics that makes this specimen a Tylosaurus proriger. In most mosasaurs, the POF barely contacts the prefrontal. In some genera, such as Clidastes, the POF and prefrontal are widely separated, and the frontal itself forms the bony ridge over the eye socket. In Tylosaurus proriger, the POF overlaps the prefrontal and may have provided additional strengthening of the skull

Also shown is the flexible joint in the middle of the lower jaw (dentary). This structure allowed the lower jaw to flex outward and enabled the animal to hold and swallow large prey in a manner similar to snakes..

(ABOVE) The business end of a mosasaur, showing the extension of the premaxilla over the most anterior teeth which is also typical of Tylosaurs. In some fossil remains, the premaxilla shows evidence of being used as a 'battering ram'. The joint between the premaxilla and maxilla is shown between the second and third teeth on the upper jaw. Pits shown in the upper and lower jaws are probably openings for blood vessels and nerves.

(ABOVE) Another shot of the anterior end of the skull, showing the left nasal opening (nares). In this specimen, the nares are located slightly forward of the location typical in later examples (and the type specimen) of Tylosaurus proriger. This may be an indication that this specimen has transitional characters linking it to an earlier species of Tylosaurus.

(ABOVE) The top of the skull, showing the location of the frontal and parietal bones. Apparently, after the animal died, the skull came to rest in an upright position on the sea floor. After some period of time (oysters had time enough to colonize what would become the lower side of the fossil!), the skull came apart and slumped over on it's left side where the top of the skull was preserved in the same plane as the left side.

(ABOVE) The back of the skull showing the connection of the quadrate (center) with the squamosal bone of the skull and the articular of the lower jaw. Small bone to the right of the quadrate is part of the atlas vertebra, most of which is located behind the squamosal. Small bones to the left of the quadrate are apparently from one of the front paddles.

(ABOVE) A close up of the quadrate showing evidence of soft tissue preservation (probably the tympanic membrane / ear drum). Although completely at home in the ocean, mosasaurs had evolved from terrestrial lizards and certainly had a sense of hearing.

Credits: The opening picture on this page is from a photograph of a nearly complete, 28 foot long Tylosaurus proriger specimen on display at the American Museum of Natural History. This specimen is about the same size as our material, but is probably somewhat younger.