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Page:Popular Science Monthly Volume 72.djvu/563

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559
THE DAWN OF QUADRUPEDS

and relationships of animals farther and farther back into geological time. There was a time, not many decades ago, when people knew nothing of the animals of the ancient days. During the life of Cuvier the knowledge of extinct animals had not progressed much farther back into geological time than the Cretaceous or Jurassic. It was just four years before his death that Jaeger made his important contribution to the Triassic fauna of Europe by the description of the remains of Mastodonsaurus, which he had in 1824 described as Ichthyosauri. Subsequent researches by a host of observers have carried our knowledge of animals into an antiquity which had not been expected.

The animals which it is our purpose to treat here are the ancestors of the modern Amphibia. There are few groups of vertebrates whose phylogeny is more obscure than that of our common toads, frogs and salamanders. It is the popular idea that these animals are unknown back in geological time, but that they are of a rather recent origin. As a matter of fact the present-day amphibians are the descendants of the oldest group of vertebrated animals with the exception of the fishes. Our knowledge of the fishes begins near the dawn of animal life on earth, and their remains are preserved in the rocks of the Ordovician age, just west of CaƱon City, Colorado, and in the Big Horn Mountains, Wyoming. Our knowledge of the amphibians begins just two ages later, and in the Devonian rocks of Pennsylvania are found the earliest traces of quadrupeds on earth. These evidences consist in footprints found by Isaac Lea in 1849 and the announcement of his discovery was given to the British Association for the Advancement of Science by Buckland in that year. These footprints represent a rather large animal which may have attained a length of several feet. The footprints were found impressed in the "Old Red Sandstone" of Pennsylvania which forms a part of the Catskill formation of that state. Marsh, forty-seven years later, announced the discovery of similar footprints from the same horizon and near the same locality but does not mention the discoveries of Lea. From these tracks in the Devonian to the deposits in the Allegheny series of the Pennsylvanian our knowledge of the Amphibia is a blank. There is not a trace recorded of any amphibians in the rocks of the Mississippian or in the Pottsville of the Pennsylvanian.

In the Allegheny series, there are several deposits in the United States, and probably one in Canada, which have produced remains of the early quadrupeds. The principal localities are in Illinois, Pennsylvania and Ohio. From the last named state great numbers of these paleontological treasures have been recovered and are preserved in the museums of the east. The most interesting place which has kept for us a record of the amphibian life of this far-off time is a deposit of coal in the eastern part of Ohio in the northern part of Jefferson county.