Currently, about 50,000 vertebrate species are known. These species vary in size, shape, habits and live in diverse habitats ranging from the bottom of the oceans to the tops of the mountains. This extraordinary diversity is the product of hundreds of millions of years of evolution.
Vertebrates are animals of the phylum of chordates that have spine. We humans also belong to the string of the animal kingdom.
According to current scientific knowledge, the oldest vertebrates were closely related lamprey aquatic animals. They had no jaws (structure that articulates in the mouth and allows chewing movement) and had a heavy bone carapace that completely covered them.
Today, the most likely hypothesis states that the current bony fish originated from jawless fish. It is also believed that amphibians originated from bony fish, and from these came reptiles. Reptiles in turn gave birth to birds and mammals.
In the evolutionary history of vertebrates, the effective occupation of the terrestrial environment came to occur with reptiles, thanks to some characteristics of these animals, such as the shell egg (which protects the embryo from dehydration), dry skin and more efficient lungs.