Leptolepis

Leptolepis ("Delicate Scale") is an extinct genus of teleost fish that lived from the Middle Jurassic period until the Early Cretaceous. The genus is one of the earliest recognized teleost genera.

Appearance
Leptolepis was about 30 centimetres (12 in) long, and resembled a modern herring, although it was not a close relative of those fish. It was the first true bony fish to really live up to the name, possessing a skeleton completely made of bone[citation needed]; 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.[3]

Mass graves of Leptolepis have indicated that it 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 after 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.[4] A 13 centimetres (5 in) fish that was deeper bodied than its co-occurring contemporaries Morrolepis and Hulettia.[4] The Morrison cf. Leptolepis probably had a live mass of about 37 grams (1.3 oz).[4] It is the only teleost fish known from the formation and was morphologically more highly derived than other Morrison fish.[4] A specific example of apomorphy in cf. Leptolepis is its "more modern tail structure" compared to Morrolepis.[4] It is believed to have fed on contemporary fish and small invertebrates.