Chapter 32 - Deuterostome Animals - 32.4 - Life on Land Contributed to Vertebrate Diversification - 32.4 Recap - Learning Outcomes - Page 707: 2

Modern mammals emerged after the extinction of non-avian mammals. The three major animal groups are the prototherians, the marsupials and the eutherians, totaling approximately 5700 identified species. The apparent diversity of mammals is the result of millions of years of evolution; since mammals are some of the most evolutionarily advanced animals, they have had the longest amount of time to diverge and improve themselves.

Modern mammals emerged after the extinction of non-avian mammals. The three major animal groups are the prototherians, the marsupials and the eutherians, totaling approximately 5700 identified species. The apparent diversity of mammals is the result of millions of years of evolution; since mammals are some of the most evolutionarily advanced animals, they have had the longest amount of time to diverge and improve themselves.