Leptolepis

Leptolepis ("delicate scale") is an extinct genus of teleost fish that lived in freshwater and marine environments from the Middle Triassic period until the Early Cretaceous. The genus is one of the earliest recognized teleost genera.
Fossil record.
As mentioned earlier, fossils of "Leptolepis" are found in freshwater and marine strata from the Middle Triassic until the Cretaceous (age range: from 242.0 to 112.6 million years ago.). Fossils are known from several localities in Eurasia, North America, Africa and Australia.
Appearance.
An average individual of "Leptolepis" was about long, and superficially resembled the unrelated modern herring. It was the first true bony fish to really live up to the name, possessing a skeleton completely made of bone; some previous genera such as "Pholidophorus" had skeletons composed of bone and cartilage. Another modern development in "Leptolepis" were its scales, which lacked the covering still present in previous genera. These two developments made swimming easier, as the bony spine was now more resistant to the pressure caused by the S movements made while swimming.
Mass graves of "Leptolepis" have indicated that species probably lived in schools which would provide some protection from predators while the creatures fed on surface plankton. "Pelagosaurus" was a known predator of "Leptolepis", as a "Pelagosaurus" fossil was found with "Leptolepis" remains in its stomach.
The Morrison cf. "Leptolepis".
Known only from a single nearly complete skeleton found at Rabbit Valley, Colorado. A fish that was deeper bodied than its co-occurring contemporaries "Morrolepis" and "Hulettia". The Morrison cf. "Leptolepis" probably had a live mass of about . It is the only teleost fish known from the formation and was morphologically more highly derived than other Morrison fish. A specific example of apomorphy in cf. "Leptolepis" is its "more modern tail structure" compared to "Morrolepis". It is believed to have fed on fish and small invertebrates.