Ancient Species -
Rayfinned Fish

The creatures we normally think of as "fish" are known as ray-finned fish because their fins are webs of skin supported by bony spines. The fins of more ancient fish, including sharks and rays, are lobes supported by cartilage.

Ray-finned fish of several types appeared in the Devonian Period (408 to 354 million years ago). By the late Permian Period (about 250 million years ago), fish were by far the dominant aquatic vertebrates.

From the Carboniferous to the Triassic Period (354 to 213 million years ago), the dominant were belonged to a group known as paleoniscoids. These were generally small fish covered in scales which superficially resembled the bony fish of today. The paleonicoids were extinct by the end of the Cretaceous Period (144 to 66.4 million years ago). 

Paleonicoids were replaced by a diverse group of bony fish  known as holosteans. The sole survivor of this group is the bowfin. They were dominant during the Jurassic Period (213 to 155 million years ago).

Teleosts, which are now the dominant type of  fish, first appeared late in the Triassic Period (about 215 million years ago). They became dominant by the late Cretaceous Period (144 to 66.4 million years ago). They are distinguished by a moveable upper jaw and fully symmetrical fins.
 



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