Again, certain huge fishes, whose remains are found in the Devonian of Ohio,[39] had jaws on the same plan with those of Lepidosiren, but of enormous size and strength (Figs. [113], [114], [115]), so that in this and some other points of structure they may be regarded as colossal Mud-fishes, and they must have had the same destructive powers, but on a far grander scale. They were besides clothed with heavy armour of bony scales, having some resemblance to that of those mailed fishes of smaller size already referred to, and indicating that, huge though they were, and formidable in destructive power, they also had enemies to be dreaded. These plates serve to ally them with the Ganoids, as their jaws do with Lepidosiren.
Fig. 114.—Lower Jaw of Dinichthys Hertzeri. One-sixth natural size.
Fig. 115.—Jaws of Lepidosiren. Natural size.—After Newberry.
We are thus enabled to see in the streams, lakes, and bays of the Palæozoic, harmless fishes, of the type of Ceratodus, feeding on plants, and huge precursors of the Mud-fishes darting from the depths, and provided with a dental apparatus more formidable than that of any modern fish, sufficient to pierce the strongest armour of the Ganoids, and to destroy and devour the largest aquatic animals. These huge fishes, armed with shears two or three feet in length, and capable of cutting asunder scale, flesh, and bone, are the beau idéal of destructive monsters of the deep, far surpassing our modern Sharks; and if, by means of supplementary lungs, they could breathe in air as well as in water, they would on that account be all the more vigorous and voracious.
Newberry has well remarked that while in the Devonian the Ganoids and Dipnoi were the real tyrants of the sea, as well as of the streams, in the Carboniferous they already diminish in size, though still abundant as to numbers, and are more limited to estuaries and fresh waters. Thus their departure from power had already begun, and went on until in modern times the proportion of Ganoids to ordinary fishes is, according to Günther, nine out of 9,000. The Carboniferous, indeed, very specially abounds in small Ganoids, though there are many large and formidable species. One of these smaller species, a very beautiful little fish, of fresh-water ponds and streams in the older part of the Carboniferous age, is represented of the natural size in [Fig. 116], and is not a restoration, being found preserved entire, though flattened, in a fine bituminous shale, which has perfectly preserved even the most delicate sculpturing of its bony scales.