These deposits are in the form of a thick bed of coal which has been opened up by modern industry which has cast aside as useless the blocks on which are preserved the priceless relics of the creatures of this bygone time. There have been great numbers of these blocks of coal collected by geologists, but in all probability the greater part of the animal remains preserved in the coal has gone to furnish heat for the people of the region.
The animals, which have been obtained from the old Diamond mine near the village of Linton, Ohio, are imbedded in the coal which formed from the vegetation growing on the shores of the lake in which the coal accumulated. This old lake was probably of but limited extent and may not have measured more than six miles in its greatest diameter. In this lake lived and died for ages the animals whose remains represent the first recorded appearance of quadrupeds on the earth. There are, to be sure, deposits in Illinois which are of contemporaneous age, but so far only five specimens of amphibia have been discovered in these deposits, so they are hardly to be taken into account when compared to the hundreds of specimens obtained by Dr. J. S. Newberry from the Linton locality. The animals which disported themselves in this old lake, at their death fell to the bottom and their remains, what was left of them after their former companions had feasted on their bodies, were covered with the mud and vegetation which drifted in upon them. Thus they are preserved to us.
The student of these remains finds them greatly different from the amphibians of to-day. There were some forms which were large, but the majority of them were small. Some may have reached a length of ten feet while a great many did not exceed six inches and a few were less than five in extent. There is one little form from Illinois, to be described further on, which barely attained a length of two inches in the adult state. Some of the Amphibia from the Linton mines represent snake-like forms with the proportions of the modern whip snake of the western plains, though not with its dimensions. Others more nearly resembled the modern lizards and this resemblance was carried to the extent of the possession of strong teeth and clawed digits. There was no osseous carpus and tarsus, however, so that they are distinct from the lizards structurally. Still other of these early quadrupeds must have resembled the modern crocodiles in appearance and a few may have attained nearly the dimensions of these forms. There were forms which were partially protected by hard dermal plates, at least on some parts of the body. Some, like the fishes, had rounded scales which covered the entire body, while a few appear to have been entirely naked. All the forms appear to have possessed the ventral armor of dermosseous rods or scutes which protected the abdomen much as the abdomen of the Sphenodon of New Zealand is protected to-day.
- Newberry, J. S., 1889, Monograph U. S. G. S., Vol. XVI., p. 211.