Cenozoic migration of a desert plant lineage across the North Atlantic

Previous paleobotanical work concluded that Paleogene elements of the sclerophyllous subhumid vegetation of western Eurasia and western North America were endemic to these disjunct regions, suggesting that the southern areas of the Holarctic flora were isolated at that time. Consequently, molecular studies invoked either parallel adaptation to dry climates from related ancestors, or long-distance dispersal in explaining disjunctions between the two regions, dismissing the contemporaneous migration of dry-adapted lineages via land bridges as unlikely.We report Vauquelinia (Rosaceae), currently endemic to western North America, in Cenozoic strata of western Eurasia. Revision of North American fossils previously assigned to Vauquelinia confirmed a single fossil-species of Vauquelinia and one of its close relative Kageneckia.We established taxonomic relationships of fossil-taxa using diagnostic character combinations shared with modern species and constructed a time-calibrated phylogeny.The fossil record suggests that Vauquelinia, currently endemic to arid and subdesert environments, originated under seasonally arid climates in the Eocene of western North America and subsequently crossed the Paleogene North Atlantic land bridge (NALB) to Europe. This pattern is replicated by other sclerophyllous, dry-adapted and warmth-loving plants, suggesting that several of these taxa potentially crossed the North Atlantic via the NALB during Eocene times.

Automated summary

Previous research suggested that the sclerophyllous subhumid vegetation in western Eurasia and western North America during the Paleogene period was endemic to these disjunct regions, implying isolation between the southern areas of the Holarctic flora. However, a recent study discovered the presence of Vauquelinia, which is currently endemic to western North America, in Cenozoic strata of western Eurasia. The fossil record suggests that Vauquelinia and other dry-adapted plants potentially migrated across the Paleogene North Atlantic land bridge during the Eocene.