Research the group sarcopterygii and explain why all terrestrial vertebrates from cows to humans are included in this group which describes fish?

Even though sarcopterygians are fishes, they are the common ancestor of all the tetrapodes (we humans included). Sarcopterygians have lobe-fins which are muscular fins with a single bone that articulates with the rest of the body. Lobe-fins are basically limb precursors. In fact, every vertebrate have lobe-limbs that originated from the lobe-fins of the sarcopterygians, so in a very real sense er and all the vertebrates alive are descendants of the sarcopterygians fishes that lived in the Devonian 419.2 million years ago.