Page:Popular Science Monthly Volume 53.djvu/229

Rh. It is expected that in the Fort Pierre formation of the Dakota region other species will be found, as it has been but imperfectly explored. Europe has about a dozen species, and New Zealand several more. Probably only about forty species of twice as many alleged to have been discovered in the world will stand the test of critical examination.

Of plesiosaurs, America has produced about ten and the Old World many more species that will stand. Many species of ichthyosaurs are recorded from Europe, India, Africa, Australia, New Zealand, and the arctic regions, and one or two in America, the toothless Baptanodon from the Jurassic of Wyoming being the type. All three groups had paddles with webbed digits, but none had claws. Williston thinks that the ancestors of the mosasaurs were land lizards. Dollo thinks that the ancestors were the peculiar group of lizards which appeared in the commencement of the Cretaceous known as Dolichosauria. Baur would derive the mosasaurs from even more specialized lizards, and believes that their relationship is very close to the monitors of the present day.

The ichthyosaurs are thought by Cope to be derived from Homœosaurus (beakless lizards) of the Jurassic; and these from the Palæohatteria (ancient hatteria), a rhynchocephalian (snout-head) which flourished as early as Permian times; and these from the Labitosaurus, an ancestor below the Carboniferous in the Palæozoic age; from which also sprang the lizardlike saurians, the dimetrodons (Otocœlius), which gave origin to the turtles (Testudinata). Some members of the group to which the plesiosaurs belong were land animals, and hence the origin of the whole group is clearly from land species. It is not now presumed that the marine saurians had much power of progression on land, but they may have climbed on to the beaches to lay their eggs. It is further presumed by Morris that in later times the eggs of saurians were devoured by other animals, contributing to the extinction of all saurians.

Three species of representative genera of Kansas mosasaurs have been restored by Williston from material in the University of Kansas.

Clidastes velox (Marsh) is a typical mosasaur, the perfected skeleton of which is twelve feet in lenthlength [sic]. Pumilus, of the same genus, is given as six feet in length, which would rank it as perhaps the smallest mosasaurian. The clidastes of Kansas had short, powerful propelling tails, which would indicate a lesser speed than that of their longer-tailed contemporaries. The clidastes had small hind limbs, showing further deficiency in speed. The animals were