Page:Popular Science Monthly Volume 27.djvu/631

Rh order, which occupied the earth at one (an early geological) period. As reptiles are inferior to mammals in the scale, so they are of earlier origin. The primitive reptilian order first appeared in force on the earth during the Permian epoch—that populous time which immediately followed the age of the true coal. If it existed during the coal measures proper, it has not yet been found in them in North America. This order has been named the Theromorpha. Its representatives have been found in Russia, Germany, South Africa, Illinois, Texas, and France. I give the names in the historic order of discovery. It embraced both carnivorous and herbivorous forms, and species of sizes from that of the Malayan tapir downward. Those with piercing teeth occur everywhere, and those with grinding teeth in North America only. South Africa furnishes us with genera with leaf-shaped teeth, and others with no teeth at all. This order represents the first air breathing land-population of vertebrates, and they evidently fulfilled most of the functions of the mammalia of to-day, though none of them were fliers, so far as known. Many of them had strange physiognomies, with blunt noses and large nostrils, and long teeth mingled with other smaller ones. Besides having given origin to most of the reptilia, this order presents many points of resemblance to the mammalia. Some of the bones resemble very closely those of the duck-bill or Platypus of Australia, and some of the bones of the skull are more mammalian than the corresponding parts of any other reptiles. It is probable that the lowest order of mammalia, which is to-day represented by the duck-bill (the Monotremata), were derived from the Theromorpha. (See "Proceedings" of the American Association for the Advancement of Science for 1884.)

The different lines of reptiles have been traced less completely than those of the mammalia, partly because their history is more ancient, and the formations where their remains are preserved have suffered greater disasters. The changes that have appeared with advancing time have been in the bones of the shoulder-girdle and pelvis, in the limbs, vertebræ, and skull. Certain changes in these parts resulted in the appearance, in the period immediately following the Permian (the Triassic), of the orders of the sea-saurians, the flying saurians, and the land-saurians or Dinosauria. In the next period, the Jurassic, we have the first certain knowledge of the tortoises and lizards; while, in the following ages of the Cretaceous, we get the pythonomorphs and the snakes. All of the existing orders were in the world by the beginning of Tertiary time, but the great monsters that characterized the middle period of the earth's history were only represented by the crocodile branch of the Dinosauria.

The changes of structure which these several lines underwent in the course of the ages were quite different from those which the history of the mammalia exhibits. Instead of becoming more perfect organs of locomotion, the limbs, if we except those of the flying