See text. The Pleistocene ('plaɪstəsin is the epoch from 18 million to 10000 years BP covering the world's recent period Chordates ( Phylum Chordata) are a group of Animals that includes the Vertebrates together with several closely related Invertebrates Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands See also Evolution of mammals Eutheria ("true beast" are a group of Mammals consisting of Placental mammals plus all extinct Mammals The Euarchontoglires (synonymous with Supraprimates) are a Mammalian superorder based on molecular genetic sequence analyses and Retrotransposon presence/absence Rodentia is an order of Mammals also known as rodents, characterised by two continuously-growing incisors in the upper and lower jaws which must Suborder Myomorpha contains 1137 species of mouse-like Rodents nearly a quarter of all Mammal species Muroidea is a large Superfamily of Rodents It includes Hamsters Gerbils true mice and Rats and many other relatives Muridae is the largest family of Mammals It contains over 600 species found naturally throughout Eurasia Africa and Australia The Old World rats and mice, part of the Subfamily Murinae in the family Muridae, comprise at least 519 species In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank.