Laurasian legacies in the Gondwanan tree fern order Cyatheales

Abstract

AO_SCPLOWBSTRACTC_SCPLOWPresent-day geographic and phylogentic patterns often reflect the Gondwana-Laurasia separation and subsequent history of continental drift. However, some lineages show non-overlapping fossil distributions relative to extant species and in some cases extant Gondwanan lineages have Laurasian extinct relatives. Here, I combined distribution data for 101 fossils and 442 extant species of tree ferns (Cyatheales) to reconstruct their biogeographic history over the last 220 million years. The time calibrated tree showed most tree ferns families originating during the Jurassic and the onset of crown group diversification beginning during the Cretaceous; a major shift in diversification rates occurred in the largest tree fern family (Cyatheaceae) that comprises ~90% of extant diversity in the group. Biogeographical reconstructions based on extant distributions alone supported a Gondwanan origin for the group; the most probable ancestral range encompassed Australasia and South America. Alternatively, incorporating fossil distribution data into reconstructions showed a Laurasian origin and a most probable ancestral range in Eurasia. These results evince the Laurasian legacies of the Cyatheales spanning the Triassic-Cretaceous, which otherwise remain hidden from biogeographic inferences. These results show that extant-only biogeographic analyses are limited when fossils distribution are more wide spread than in the present-day, highlighting the need to directly incorporate fossils into biogeographical analyses and improve the reliability of ancestral geographic range estimation.