Fig. 309. Carboniferous Brachiopods
A, Productus; B, Spirifer, the right-hand figure showing the interior with the calcareous spires for the support of the arms
Fishes still held to the Devonian types, with the exception that the strange ostracoderms now had perished.
Amphibians. Footprints of amphibians are found in the Devonian. The earliest Carboniferous amphibians were small newtlike creatures possessing not only the typical amphibian double breathing system of gills and lungs but also a double locomotive apparatus of short, weak legs for crawling on land and a tail for propulsion in the water. They branched into a variety of types,—some large and crocodilian, some with well-developed legs for running, some with large heads like giant tadpoles, and some eel-like and limbless.
Fig. 310. A Carboniferous Dragon Fly
One tenth natural size
Fig. 311. A Carboniferous Amphibian
The earliest amphibians differ from those of to-day in a number of respects. They were connecting types linking together fishes, from which they were descended, with reptiles, of which they were the ancestors. They retained the evidence of their close relationship with the Devonian fishes in their cold blood, their gills and aquatic habit during their larval stage, their teeth with dentine infolded like those of the Devonian ganoids but still more intricately, and their biconcave vertebræ which never completely ossified. These, the highest vertebrates of the time, had not yet advanced beyond the embryonic stage of the more or less cartilaginous skeleton and the persistent notochord.