Tylosaurus proriger after Osborn, 1899. See Credits below.


Copyright 2000-2009  by Mike Everhart

Last updated: 03/26/2009

Naming the first mosasaur from Kansas  

As a bit of historical background, the type specimen of Tylosaurus proriger (MCZ 4374) was discovered near Monument Rocks in Gove County by "Col. Connyngham and Mr. Minor,"and was obtained by Professor Louis Agassiz during his 1868 visit to western Kansas. It was the first mosasaur to be described from Kansas and was originally named “Macrosaurus” proriger by E. D. Cope. The description of the new species by Cope (1869) in the minutes of the Academy of Natural Sciences of Philadelphia meeting of June 1, 1869 was brief by modern standards:

He [Cope] made some remarks on a fine fragment of the muzzle of a large Mosasauroid, which pertained to a cranium of near five feet in length. The pterygoid bones were separated from each other, and support nine teeth. A peculiarity of physiognomy was produced by the cylindric prolongation of the premaxillary bone beyond the teeth, and a similar flat prolongation of the extremity of the dentary. He referred the species to Macrosaurus Owen, under the name M. proriger.”

The following year, Cope (1870, pl. 12, figs 22, 23) described the same specimen more completely, figured it and, with little explanation, referred it to another European genus, Liodon Owen. Two years later, O.C. Marsh, apparently recognising significant differences between the American and European mosasaurs, proposed a new genus (Rhinosaurus: meaning nose-lizard) from a more complete specimen (YPM 1268 - Rhinosaurus micromus) he had collected ‘on the south side of the Smoky Hill River’ in 1871. However, that name was preoccupied and Cope (1872) proposed the genus name Rhamphosaurus. In a brief note, Marsh (1872b, p. 147) wrote that:

“As this name [Rhinosaurus] proves to be preoccupied, it may be replaced with Tylosaurus. The name Rhamphosaurus, since suggested by Prof. Cope, cannot be retained, as it was given to a genus of lizards in 1843 by Fitzinger.” Leidy (1873, p. 274) was the first to placeMacrosaurus’ proriger Cope, 1869 into Tylosaurus Marsh.

Figure 1: A lateral view of the skull of Tylosaurus proriger; About 4 feet (1.2 meters).

Figure 2: A dorsal view of the skull of Tylosaurus proriger.

Figure 3: A ventral view of the skull of Tylosaurus proriger.

Tylosaurus proriger; modified from a very large drawing in Part IV, Osborn, H.F. 1899. A complete mosasaur skeleton, osseous and cartilaginous. Memoirs of the American Museum of Natural History 1(4):167-188.