Skeletal changes of vertebrates transitioning from water to land
As tetrapodomorph vertebrates began colonizing land during the Late Devonian and Early Carboniferous, their bodies began evolving anatomical traits better adapted for life away from water. Skeletal innovations conventionally associated with terrestrially first appeared in aquatic elpistostegalians such as Panderichthys rhombolepis, Elpistostege watsoni, and Tiktaalik roseae.
Source: Wikipedia — Skeletal changes of vertebrates transitioning from water to land (CC BY-SA 4.0)