What are the reasons for the diversity of the modern animal world on our planet?

The variety of animals on our planet is due to a long history of evolution, the influence of the environment, the ability of animals to adapt to new conditions, etc. This can be understood by the example of representatives of the same family, like canines (relatives of a dog). So, for example, living in the northern plains and forests, wolves have become quite tall and heavy, which allows them to hunt big game. And there are dogs that live in water almost all their lives and have membranes between their toes (in South America).