The Iberian fossil record of †Otodus megalodon rejects Mediterranean dwarfism and supports nursery use.

†Otodus megalodon, the largest known macropredatory shark, was globally distributed from the Miocene to Pliocene, yet most ecological and palaeobiological inferences rely heavily on American collections. This geographical bias limits understanding of its population structure and life-history strategies elsewhere. Two explanations have been proposed for its body-size patterns: a Bergmann-type cline, with larger individuals at higher, cooler latitudes and a related hypothesis of Mediterranean dwarfism; and the influence of localized nursery areas that generate assemblages dominated by small juveniles, as documented in several American sites and the Reverté quarries in the western Mediterranean. Here, we present the first extensive dataset outside the Americas designed to test these alternatives across two adjacent basins. Body-size estimates show no significant difference between Atlantic and non-Reverté Mediterranean populations, whereas the Reverté assemblage is smaller. This pattern contradicts basin-wide Mediterranean dwarfism and does not support a Bergmann-type size-latitude relationship. Instead, it strongly indicates a localized nursery at Reverté. More broadly, the results align with an emerging view of widespread nursery habitats in †O. megalodon, comparable to those of extant sharks. By filling a key regional gap, the Iberian record provides tests of competing hypotheses and refines understanding of †O. megalodon population structure and life history.