Leptolepis: an early teleost from Jurassic seas

Leptolepis is a genus of small ray-finned fishes best known from Jurassic marine deposits in Europe. Its articulated fossils preserve the light scales, skull and tail of an early teleost lineage, while successive revisions have removed many unrelated fishes once placed under the same name. The dense “herring” slabs from Solnhofen often invoked as Leptolepis shoals are generally assigned to Leptolepides. These distinctions make the genus a useful case in the ancient fish catalogue.

Quick facts

A name that once gathered many small fishes

Louis Agassiz established Leptolepis in 1832. The type species, L. coryphaenoides, was described earlier by Heinrich Georg Bronn as Cyprinus coryphaenoides. During the nineteenth and twentieth centuries, paleontologists used Leptolepis broadly for small, streamlined Mesozoic fishes with a superficially similar appearance. Later comparative work showed that this broad usage combined distinct genera and lineages.

That history affects how range and ecology should be reported. A fossil labelled Leptolepis in an old collection may not belong to the modern, narrower concept of the genus. The type species and well-described related forms provide the safer basis for discussing the animal. The name is a taxonomic hypothesis tied to diagnostic anatomy, not a label for every small fish that resembles it.

What the German Toarcian fossils preserve

Material from the late Early Jurassic fossil sites of Grimmen and Dobbertin in Mecklenburg–Western Pomerania includes Leptolepis coryphaenoides, L. normandica, L. jaegeri, a possible Proleptolepis and other specimens left in open nomenclature. The fish come from the “Green Series,” in the lower part of the early Toarcian Harpoceras falciferum ammonite zone.

Complete skeletons are uncommon in the sample, but many fossils preserve articulated skulls with little compression; some are close to three-dimensional. Researchers can examine the premaxilla, maxilla and dentary, the preoperculum, sensory canals and tooth arrangement. These structures give a firmer basis for comparison than body outline alone. The northeastern German occurrences also extend the known distribution of several species across the Central European epicontinental sea during the early Toarcian.

A light-bodied early teleost

Well-preserved specimens show an elongate, streamlined fish with cycloid scales and a forked tail whose external outline appears nearly symmetrical. The tail's internal skeleton retains features that matter to the evolutionary interpretation, so its silhouette should not be confused with a modern teleost tail built in exactly the same way. The skull and jaws also show a suite of characters used to place leptolepids among early teleosts.

These fossils help document early teleost diversity, but they do not establish that Leptolepis was the direct ancestor of all living bony fishes or of modern herrings. Phylogenetic analyses place it among stem teleost lineages alongside other early forms. Similar body shapes may reflect efficient swimming in open water rather than close relationship.

Size, food and the shoaling question

Many specimens are around 10–20 centimetres long, though the value depends on species and growth stage. A small mouth and slender body are consistent with taking small aquatic prey, perhaps planktonic or nektonic animals. The cited fossils do not preserve a secure stomach meal that would specify a regular diet. Food claims should therefore remain at the level of functional inference.

Schooling is plausible for a small pelagic fish, and artists often show leptolepids in groups. Yet the famous slabs from the Solnhofen Limestone that were long described as masses of Leptolepis sprattiformis largely belong to Leptolepides sprattiformis, a genus separated in later work. Dense fossil accumulation can result from transport, trapping, or repeated deposition and does not by itself prove that the fish swam in a coordinated school.

Preservation is not a colour photograph

Early Jurassic Posidonia Shale deposits formed in a marine setting where bottom waters could become oxygen-poor. Fine sediment and limited disturbance helped preserve compressed fish skeletons. Even a striking slab records mineralised anatomy after decay, burial and compaction; bones may shift, and soft tissues usually disappear.

A dark back and pale underside are common camouflage in modern open-water fishes, but no preserved pigment pattern cited for Leptolepis demonstrates that colour scheme. The genus is significant because its skeletons preserve early teleost anatomy, not because every aspect of its life is known. Keeping articulated evidence separate from ecological analogy makes its place among Jurassic fishes clearer.

Explore related evidence in the ancient fish catalogue.