A state-of-the-art review of the Cenozoic fossil recordfrom Western Amazonia is provided, based on literatureand new data (regarding Paleogene native ungulates). It allowssummarizing the evolution and dynamics of middleEocene–Holocene mammalian guilds, at the level of species,families, and orders. Major gaps in the Western Amazonianmammal record occur in the pre-Lutetian and early Mioceneintervals, and in the Pliocene epoch. Twenty-three orders, 89families, and 320 species are recognized in the fossil record,widely dominated by eutherians from the middle Eocene onward.Probable Allotheria (Gondwanatheria) occur only in theearliest interval, whereas Metatheria and Eutheria are conspicuouscomponents of any assemblage. Taxonomic diversitywas probably fairly constant at the ordinal level (~12–14 ordersin each time slice considered) and much more variable interms of family and species richness: if most intervals arecharacterized by 40–50 co-occurring species and 19–31 cooccurringfamilies, the early Miocene period illustrates a depauperatefauna (21 species, 17 families), strongly contrastingwith the late Miocene climactic guild (82 species, 38 families).Recent mammalian taxonomic diversity from WesternAmazonia (12 orders, 37 families, and 286 species) is at oddswith all past intervals, as it encompasses only three orders ofSouth American origin (Didelphimorphia, Cingulata, andPilosa) but four North American immigrant orders(Artiodactyla, Perissodactyla, Carnivora, and Lagomorpha).In terms of taxonomic diversity, recent mammalian guildsare fully dominated by small-sized taxa (Chiroptera,Rodentia, and Primates). This overview also confirms thescarcity of large mammalian flesh-eaters in ancientNeotropical mammalian assemblages. The pattern and thetiming of mammalian dispersals from northern landmassesinto Western Amazonia are not elucidated yet.