A Mexican Quaternary mammal database is presented with more than 15,000 records, representing 12 orders, 43 families, 146 genera, and 274 species, known from over 770 localities. One third of these taxa no longer occur in Mexico, either because they are extinct or because they occur in different areas. The order Notoungulata is extinct worldwide, while Proboscidea no longer occur in the Americas. Other families, such as Herpestidae and Equidae, also are no longer present. Three families have been extirpated from North America (Camelidae, Hydrochoeridae, and Megalonychidae) while five others are extinct (Gomphotheriidae, Mammutidae, Glyptodontidae, Megatheriidae, and Mylodontidae). Of the 146 genera, 29 are extinct (19.9 %) and nine are considered extirpated (5.5 %); and at the species level, 77 are extinct (28.1 %) and seven are extirpated from the country. Analysis of the data clearly indicates that the fossil record is biased toward the medium- and large-sized animals. In examining this bias, only the extinct species of the Artiodactyla, Notoungulata, Perissodactyla, and Proboscidea are considered as well as those of the Xenarthra and Carnivora that weighed more than 100 kg. Out of 61 of these species, 50 become extinct at the end of the Pleistocene. This group includes many megaherbivores together with the megacarnivores. Many species expand their distribution to different latitudes or higher or lower altitudes or moved further north or south during the Pleistocene. Tropical mammals tend to move like mammals of temperate climates. The current distribution pattern of several groups of species can be explained as a result of the effect of Pleistocene glaciations.