Paleonisciformes is an extinct group of fish that lived during the Paleozoic and Mesozoic eras, approximately 400 to 100 million years ago. They are characterized by their streamlined bodies, ganoid scales, and a unique jaw structure. These fish were primarily freshwater dwellers and are considered ancestors of modern bony fish. The group includes several families, such as Paleoniscidae and Lepidotes, which showcase a variety of sizes and adaptations. Fossils of Paleonisciformes have been found in various locations worldwide, providing valuable insights into the evolution of early fish and aquatic ecosystems.