Sarcopterygii is a class of fish known as lobe-finned fish, characterized by their fleshy, lobed fins that are supported by bone structures. This group includes both extant species, like coelacanths and lungfish, and extinct species that are important for understanding the evolution of vertebrates. Sarcopterygii are significant because they are believed to be the ancestors of all land vertebrates, including amphibians, reptiles, birds, and mammals. Their unique fin structure is thought to have played a crucial role in the transition from water to land, making them a key focus in evolutionary biology.