Issingius

Issingius is a genus of extinct ray-finned fish that lived during the Triassic period. Fossil remains of Issingius have been found primarily in the Issing locality in Bavaria, Germany, which gives the genus its name. These fossils date back to the Middle Triassic, specifically the Anisian stage.

The fish were relatively small, with body lengths typically not exceeding 10 centimeters. They possessed a fusiform or somewhat elongated body shape, common among many early bony fishes. Key anatomical features of Issingius include a prominent dorsal fin and a caudal fin that appears to have been heterocercal, meaning the upper lobe was larger than the lower lobe, though this can vary in interpretation. The scales were cycloid or rhomboid, depending on the species and preservation. Its teeth were small and numerous, suggesting a diet of small invertebrates or planktonic organisms.

Issingius is considered part of the palaeonisciformes, an extinct order of ray-finned fishes that were widespread during the Paleozoic and Mesozoic eras. The discovery of Issingius has contributed to our understanding of early teleost evolution and the diversification of fish life following the Permian-Triassic extinction event. The fossils are often found in fine-grained sedimentary rocks, indicating deposition in calm, lacustrine or marine environments. Several species have been described, including Issingius pictus, which is often cited as the type species. The exact phylogenetic relationships of Issingius within the palaeonisciforms are still subject to ongoing research and debate among paleontologists.