Page:Popular Science Monthly Volume 53.djvu/237

Rh as a "lizardlike bird"; it was no more like a bird than is a bat; it was a birdlike reptile. These suggestions certainly point to the necessity of a revision of the text-books and charts in use in class rooms, which in many instances should become obsolete because of perfected restorations.

Specialists regard the marine saurians as having existed some millions of years ago. They conclude that these animals had at least a million years of existence in various forms. While it may be venturing



into the domain of the encyclopædia to state the causes of these conclusions, a word here may not be out of place. The Cretaceous formation, in which the marine saurians are found, is of chalk, green sands, etc., and ranges in thickness from ten thousand to twenty thousand feet or more. It existed in the last part of the Mesozoic realm. From the thickness and position in geological strata scientists deduce its age and place in Nature. As the remains of marine saurians are found only in the Cretaceous deposits, specialists speak of them as existing several million years ago. At that time were numerous fishes, birds, reptiles, and plants.

On previous pages some remarks have been passed in reference to origin and distribution of the sea saurians. It may not be out of place to exploit further the evolution and sequence of other saurians existing before and contemporaneously with the salt-water group. To do so in a brief way presupposes that the reader has some general knowledge of the times in which these remarkable animals existed. The evolution of animal life can only be discussed in general terms, as completer skeletons are needed to determine the whole subject.

The duration of saurians extended from the Carboniferous period of the Palæozoic realm through the entire Mesozoic realm which followed. The original saurian, so far as discovery to date shows, was a cotylosaur, found in the coal measures of Ohio by the late Professor Cope. This ancestor, Isodectes punctulatus (Cope), was eight