Mosasaurinae · Latest Cretaceous
Mosasaurus hoffmannii
/MOH·zuh·sor·us/ · "Meuse lizard", for the river near its discovery
The giant that gave the whole group its name — the apex predator of the last seas of the Cretaceous, and a fossil that helped prove extinction was real.
illustration plate — swimming pose, deep tail-fluke. Drop your reconstruction here.
Mosasaurus is the namesake of the entire family — the animal every other mosasaur is measured against. The largest specimens of M. hoffmannii reached perhaps seventeen metres, putting it in the size class of a modern sperm whale and at the very top of the marine food web in the final few million years of the Cretaceous.
Its story is also the story of palaeontology itself. In the 1760s, quarry workers in a chalk mine near Maastricht, in the Netherlands, struck an enormous fossil jaw. Naturalists argued over it for decades — was it a whale, a crocodile, a giant fish? In the early 1800s the French anatomist Georges Cuvier studied it and concluded it was a giant marine lizard belonging to no living group. That conclusion was revolutionary: it was powerful early evidence that whole kinds of animals could be lost forever — that extinction was real.
The Maastricht jaw gave its name not only to the animal but to the very last age of the Cretaceous: the Maastrichtian.
Mosasaurus had a deep, powerful skull, conical recurved teeth for gripping struggling prey, and the family's signature second set of teeth on the roof of the mouth. Its tail ended in a downturned fin that drove it through the water with shark-like efficiency. It ate almost anything it could catch — fish, sea turtles, ammonites, seabirds, smaller mosasaurs. Stomach contents and bite-marked bones show it was an opportunist with few, if any, rivals.
Mosasaurus lived to the very end of the Cretaceous. Like the giant pterosaurs in the air above, it was cut down at its peak by the asteroid impact 66 million years ago — the last and largest of a dynasty that had ruled the seas for barely 34 million years.