Leptolepiformes

Leptolepiformes is an extinct order of ray-finned fishes (Actinopterygii) that is traditionally regarded as among the early teleosts or as a paraphyletic assembly of stem-teleosts. The group is known from fossil assemblages dating mainly to the Late Triassic and Early Jurassic, with specimens found in Europe, North America, and Asia. Because the exact relationships of its constituent taxa are debated, Leptolepiformes has often been treated as a broad, somewhat contentious or transitional grouping within early actinopterygians.

Fossils attributed to Leptolepiformes depict small to moderately sized, streamlined fishes. They generally possess slender bodies and comparatively small or delicate scales, often of cycloid type. The anatomy of the skull and jaws shows adaptations for grasping small prey, and the fins, along with the tail, align with what is known for early teleosts. The morphological diversity within the group is notable, but many members share a general emphasis on a fast, active lifestyle in pelagic or nearshore environments.

Paleobiogeography indicates a largely European and North American distribution in the early part of their time range, with later records extending into other regions of the Northern Hemisphere. Leptolepiformes are important for understanding the early evolution and diversification of Teleostei, as they help illuminate the sequence of traits that characterize later, more derived teleost fishes. Their study contributes to broader discussions about the origin of key teleost features and the early radiation of modern-looking ray-finned fishes.

See also: Teleostei, Leptolepis, early actinopterygians.