Myrsine fossil pollen from the Oligocene of Iberia provides evidence for early Eurasian dispersal

Abstract

The Cenozoic fossil record of Myrsine (Primulaceae) in Europe is largely based on leaf macroremains of uncertain taxonomical attribution and consequently remains poorly understood. In this study, we report the first well-documented European fossil pollen record attributable to early representatives of Myrsine based on exceptionally preserved palynological assemblages from the As Pontes and Laracha basins (northwestern Spain). The studied material, assigned to Eucommiopsispollenites compactus , was analyzed using light microscopy, scanning electron microscopy, and confocal laser scanning microscopy. The pollen grains exhibit a distinctive combination of characters that allow confident attribution to extant Myrsine , including tetra- to pentacolporate apertures, short colpi, thick exine, and weakly scabrate ornamentation. The occurrence of Myrsine in Rupelian deposits dated to approximately 30 Ma demonstrates that the lineage had already reached the westernmost margins of Eurasia by the early Oligocene, shortly after the estimated origin of the crown-group in the Indo-Malayan region. This finding predates the timing proposed by current molecular biogeographic models for the colonization of the Palearctic. A reassessment of the fossil record indicates that most previous Eurasian reports of Myrsine are based on generalized laurophyllous leaf morphologies lacking unequivocal diagnostic features, whereas fossil pollen provides more reliable evidence for tracing the history of the genus. The Iberian record further supports the persistence of humid evergreen and thermophilous forests in southwestern Europe during the Oligocene and suggests that warm palaeotropical vegetation corridors across Eurasia may have facilitated the rapid dispersal of Myrsine and other palaeotropical taxa during the Palaeogene. These findings provide a calibration point for future molecular phylogenetic and biogeographic analyses of pantropical Primulaceae.