Bony fishes have internal skeletons that are mostly made from bone. They first appeared 419 million years ago and are the largest taxonomic group of vertebrates in the world. Bony fish are divided into the lobe-finned fishes (Class Sarcopterygii) and the ray-finned fishes (Class Actinopterygii).
Ray-finned fishes have dorsal (back) fins with numerous skin-covered bony rays supported at their base by parallel rows of radial bones. Most of these fish have scales that grow from their skin, but their structure varies by group.
Ray-finned fish are divided into the Polypterimformes (bichirs), Chondrostei (sturgeon, paddlefish), Holostei (gars and bowfin) and Teleostei (Teleosts; 99% of the world’s bony fish).
The name amphibian is derived from the Greek amphi meaning double and bios meaning life. This refers to the life history of most amphibians which begin life as aquatic larvae, hatching from eggs laid in water, before developing into the terrestrial adult.
Modern amphibians evolved from the (now extinct) temnospondyli in the Early Permian (290 million years ago); the earliest known frog (Genus Triadobatrachus) was alive in the early Triassic, 250 million years ago. Living amphibians have small lungs and most species exchange gases through their skins. Some salamanders in the Family Plethodontidae are entirely lungless, relying purely on their skin for respiration, thereby limiting it to moist habitats. Amphibian skin is unscaled and protected with mucus. The skin glands can also produce alkaloid toxins which can be lethal if ingested.