Tylosaurinae · Late Cretaceous
Tylosaurus proriger
/TY·loh·sor·us/ · "knob lizard", for its bony snout
A fourteen-metre hunter built around a battering-ram snout — the dominant predator of the Western Interior Seaway, the same waters Pteranodon flew above.
illustration plate — elongated body, reinforced snout. Drop your reconstruction here.
Tylosaurus shared its world with Pteranodon — one ruling the surface of the Western Interior Seaway, the other the air above it. Reaching some fourteen metres, it was among the largest mosasaurs of its time and a true apex predator of the chalk seas that once covered the heart of North America.
Tylosaurus takes its name, "knob lizard", from its most distinctive feature: a stout, bony, toothless projection at the tip of the snout. Many palaeontologists think this reinforced rostrum was a weapon — used to ram and stun prey, or to fight rival Tylosaurus, much as some modern toothed whales use their heads. The very front of the jaw was built to take an impact.
We know what Tylosaurus ate because exceptional specimens preserve their last meals. Stomach contents have included fish, sharks, smaller mosasaurs, flightless diving birds like Hesperornis, and even — in one famous case — the remains of a plesiosaur. It was a generalist apex predator that took whatever it could overpower.
Its body was long and somewhat slender, with paddle-like limbs and a powerful, deep-finned tail — built for bursts of speed in open water.
Tylosaurus thrived for several million years during the Campanian age before giving way to other giant mosasaurs like Mosasaurus and Prognathodon as the Cretaceous drew to its close. It remains one of the best-known and most completely understood of all the great marine reptiles, thanks to the rich fossil beds of Kansas and the American Midwest.