Evolution is a theory that holds that all organisms living on earth today share a common ancestor. It is believed that over generations, specific changes or adaptations have been established in species in order to help them survive, reproduce, and raise their offspring. But how can we be sure these changes have happened? Today, there is an abundant amount of research evidence suggesting that anatomical and physiological alterations occurred in species that caused them to transition from being aquatic to terrestrial animals, thus allowing them to survive in different environmental conditions. Here are several progressive changes that an aquatic organism must undergo to move to dry land and adapt to its new terrestrial habitat: the circulatory and especially respiratory systems must be improved, structural adaptations must be modified, the development of a skeletal system to protect the body. the body and organs, as well as an adjustment of the senses must also occur. The evolution from water to land was a major event among vertebrates. The respiratory, circulatory and reproductive systems of species show how they have evolved and adapted to the environment. Vertebrates belonging to the phylum Chordata had at least at one point in their lives a dorsal hollow nerve cord, a notochord, pharyngeal pouches, and a tail that extends beyond the anus. It is said that fish were among the first vertebrates. The first fish to appear in the fossil record were jawless, covered in bony plates, gills, scales, but no fins. According to Arreola, they then evolved by adapting to their environment and began to form paired jaws and fins. Jaws were useful with their muscles and teeth, which helped them eat a wider variety of foods, and were even able to defend themselves using the middle of a paper......is a form of evidence that shows how life has changed over the years and how today's species are linked to a common ancestor. Paleontologists look for characteristics from one way of life to another. They create a tree of life that separates species according to their common structure. Fossils show how tetrapod legs evolved from fins, and genetic studies show how mutation and natural selection gave rise to the long limb bones of fins (Hoff). In this case, they discovered how a species that lives on water transitioned to a terrestrial lifestyle. Perhaps his descendants found the land as an abundant food source and refuge from competition. Over millions of years, through variation and selection, fins became legs, hind legs appeared, and bodies created fur and took on the familiar shape of the animals we have on earth . These species must have evolved and changed the way