United States or Yemen ? Vote for the TOP Country of the Week !
They gradually approach the familiar types of Teleosts, so that we may say that before the end of the Cretaceous the waters swarmed with primitive and patriarchal cod, salmon, herring, perch, pike, bream, eels, and other fishes. Some of them grew to an enormous size.
TELEOSTS. The great group of fishes called the teleosts, or those with complete bony skeletons, to which most modern fishes belong, may be mentioned here, although in the Devonian they had not yet appeared. The teleosts are a highly specialized type, adapted most perfectly to their aquatic environment. Heavy armor has been discarded, and reliance is placed instead on swiftness.
None of the Teleosts had appeared until the end of the Jurassic. They now, like the flowering plants on land, not only herald the new age, but rapidly oust the other fishes, except the unconquerable shark.
It is interesting to note that the modern teleosts in their embryological growth pass through the stages which characterized the maturity of their Devonian ancestors; their skeleton is cartilaginous and their tail fin vertebrated. The Carboniferous system is so named from the large amount of coal which it contains.
Even in the Eocene, about five per cent of marine shells were of species still living, and in the Pliocene the proportion had risen to more than one half. Fishes were of modern types. Teleosts were now abundant.
The vertebrae were not ossified, for no trace of them has been found. DEVONIAN FISHES. The TRUE FISHES of the Devonian can best be understood by reference to their descendants now living. Modern fishes are divided into several groups: SHARKS and their allies; DIPNOANS; GANOIDS, such as the sturgeon and gar; and TELEOSTS, most common fishes, such as the perch and cod.
In the Cretaceous the teleosts, or bony fishes, made their appearance, while ganoids declined toward their present subordinate place. The amphibians culminated in the Triassic, some being formidable creatures as large as alligators. They were still of the primitive Paleozoic types.
Word Of The Day