In this paper, I argue that the species-as-individuals (SAI) thesis has broader and as yet unexamined metaphysical implications in that it entails a perdurantist view of biological ontology. Perdurantism holds that entities “perdure” over time by having both spatial and temporal parts and full spatiotemporal extension. Endurantism, by contrast, holds that entities “endure” over time by having only spatial parts and spatial extension, and existing wholly and completely every moment. The SAI thesis, as its principal supporters agree, is committed to perdurantism. It holds that species are “historical entities” that are “spatiotemporally localized” (Hull 1978). Spatiotemporal location is extension in both space and time, hence Hull's amplified claim that species are “spatiotemporally extended” (1989). Crane (2004) argues that if the SAI thesis is committed to a relational view of species as concrete ancestor-descendant lineages, then it has a four-dimensional view. This is in fact the predominant view of the SAI thesis (Horvath 1997). Because the parts of perduring entities must also perdure, the SAI thesis is committed to viewing organisms, as parts of species, as perduring entities. This implicit facet of SAI is reinforced by Hull's (1978) explicit reliance on Huxley's (1898) perdurantist view of biological entities. The SAI thesis thus extends perdurantism to the entirety of biological ontology. These implications should be carefully considered because the metaphysical issue of persistence is contentious and perdurantism is not universal in philosophy of biology.