The genus Mahonia in the Miocene of Turkey: Taxonomy and biogeographic implications

The genus Mahonia has a disjunct modern distribution with the New World Group Occidentales in northwestern North America and Central America and the mostly Old World Group Orientales in Central and Southeast Asia. Group Orientales has one species in North America. Morphologically, the two groups can be distinguished by two main patterns of leaf venation. Leaflets in the Group Orientales have a palmate-festooned brochidodromous venation and those of Group Occidentales usually have a pinnate-brochidodromous to (semi)craspedodromous venation, with some intermediate forms. In North America both Orientales and Occidentales can be traced from Eocene to Miocene strata. No unequivocal records of Mahonia are known from East Asia. A few Oligocene to Pleistocene fossils from Europe can be assigned to Group Orientales and to the section Horridae Fedde of Group Occidentales. Here we report two new species of Mahonia from the Miocene of Turkey, which clearly fall within the morphological range of the Group Orientales. One species, also found in the Oligocene–Miocene of western North America, is quite similar to Himalayan and East and Southeast Asian modern species. The other resembles the single modern North American member of Group Orientales. The high diversity of Mahonia in Europe and Asia Minor from the Oligocene onwards includes members of at least four lineages. The close relationships of these fossils with contemporary North American species suggest that the genus had reached western Eurasia from North America via the North Atlantic during or prior to the Oligocene. Colonization of Central and East Asia may have occurred from western Eurasia or North America, or from both directions.

► Two new species of Mahonia described are from Turkey.
► Two of the three major lineages of Mahonia were present in western Eurasia.
► Modern E. Asian species possibly migrated from Asia Minor via the Himalayan corridor.
► Fossil taxa resembling modern dry-adapted species thrived in humid temperate climate.
► Evidence for ancient western Eurasian–western North American biogeographic links.