LEPTOLEPIS

genus of marine fish thought to represent the ancestral form that gave rise to the teleosts, the dominant group of fishes in the world today. Leptolepis was abundant between 208 million and 144 million years ago in the world's Jurassic seas and was herringlike in size and appearance. Fragmentary remains from earlier and later rocks may indicate an earlier origin and longer persistence for the genus than the Jurassic period dates indicate. In many anatomical details, Leptolepis is intermediate between the more primitive holosteans and the more advanced teleost fish.