While Aristotle has conventionally been perceived as a precursor for the taxonomy of modern biological systematics, such as that of Carolus Linnaeus, this essay investigates the relationship between Aristotelian metaphysics and natural history in order to demonstrate the problem of anomalies in any system of this kind. In particular, the problem involves the place that may be given to the unnatural (deviations form the norm of nature) in a system for nature – if there can be a taxonomy of anomalies (namely, a teratology), given the logic of Aristotelian philosophy.