As a clade, the group includes all its descendants. This means it includes the Tetrapods, that is, all species of four-limbed vertebrates. The fin-limbs of sarcopterygiians are very similar to what people believe was the ancestral form of tetrapod limbs. The ancestors of tetrapods are to be found amongst the lobe-fins of the Devonian period. The term 'fishapod' is becoming used for this transitional group.