Osteíctios

Osteíctios, or bony fishes, are a major lineage of jawed vertebrates distinguished by a skeleton reinforced with bone tissue, in contrast to the cartilaginous skeletons of sharks and rays. They constitute the largest group of fishes, including both ray-finned fishes and lobe-finned fishes, and account for the vast majority of described fish species.

Key anatomical features of osteíctios include a bony endoskeleton, dermal bone in the scales, and gills covered by an operculum. Many possess a swim bladder, a gas-filled organ derived from ancestral lungs, which aids buoyancy. The skin often bears bony scales, and most species have a lateral line system that detects water movements.

Taxonomically, osteíctios are divided into two major lineages: Actinopterygii (ray-finned fishes) and Sarcopterygii (lobe-finned fishes). The Sarcopterygii include coelacanths and lungfishes; the latter groups have lungs and can breathe air. Importantly, sarcopterygian fishes are the evolutionary ancestors of tetrapods (amphibians, reptiles, birds, and mammals), with some classifications placing Tetrapoda within Sarcopterygii and hence within Osteíctios.

Evolution and diversity: The earliest osteíctios appear in the Silurian period and underwent extensive diversification during the Devonian, a time often called the "Age of Fishes." Today, osteíctios are highly diverse, with the majority of fish species belonging to the ray-finned teleosts, occupying freshwater and marine habitats worldwide.

Ecology and significance: Bony fishes inhabit nearly every aquatic ecosystem, from abyssal oceans to alpine streams. They are a central resource for human food and play a crucial role in ecological studies, fisheries management, and evolutionary biology.