Taxonomy - the study of classification - is a constantly-evolving field. Changes to species lists are regularly proposed as new physical and genetic evidence becomes available, and as different species concepts (which define what should be considered separate species) are explored. These changes regularly occur on a variety of taxonomic scales, but there is little standardization for their acceptance within the wider scientific community. This makes answering the question "How many ungulate species are there?" a challenge to answer, since there is no single response.

Four recent ungulate classifications are presented and compared below, with species grouped based on the most conservative taxonomy. The species lists range from approximately 250 species in conservative taxonomies such as Mammal Species of the World (Wilson & Reeder, 2005) and the IUCN Red List (2024) to over 450 species in Ungulate Taxonomy (Groves and Grubb, 2010). As of 2024, UltimateUngulate.com follows the taxonomy synthesized in the American Society of Mammalogist's online Mammal Diversity Database.