Gondwanan origin of the Dipterocarpaceae-Cistaceae-Bixaceae is supported by fossils, areocladograms, ecomorphological traits and tectonic-plate dynamics

Abstract

There is disparity between the estimated time of origin of the ‘superclade’ Dipterocarpaceae sensu lato, that includes Sarcolaenaceae, Cistaceae, Pakaraimaea, Bixaceae, Cochlospermaceae and Sphaerosepalaceae, as determined by recent molecular phylogenies (100−85 million years ago, Ma) and its strongly tropical, South American-African-Madagascan-SE Asian distribution that indicates an older Gondwanan origin (>110 Ma). We used several paleobiogeographic approaches, including recently reported fossil records, to explore the hypothesis that Dipterocarpaceae sl has a Gondwanan/early-Cretaceous origin.We created molecular phylogenies for this group, assigned each genus/family to the tectonic plate on which it is extant, and subjected the cladogram to areogram analysis. We also assessed ecological, mycotrophic and morphological traits, and global circulation patterns, as these might affect this group’s distribution.The initial analysis (omitting fossil evidence) showed that the crown of Dipterocarpaceae sl occurred concurrently on the South American and Madagascan plates. Including fossils from Africa and India changed this to a South American-African origin. Collectively, these origins represent NorthWest Gondwana with South America, Africa and Madagascar remaining conjoined until ≥105–115 Ma, setting the minimum age for this superclade with some evidence that it may be much older. We also show that the immediate ancestors of the three daughter lineages [Dipterocarpaceae- Sarcolaenaceae (in Africa/Madagascar, ≥115 Ma), Cistaceae- Pakaraimaea (South America/Africa/Eurasia, ≥105 Ma) and Bixaceae-Cochlospermum-Sphaerosepalaceae (South America/ Africa, ≥105 Ma)] also arose in NorthWest Gondwana.The immediate ancestors or basal species in Sarcolaenaceae, Sphaerosepalaceae, Dipterocarpaceae (both its subfamilies) and Bixaceae migrated from (South America)/Africa to Madagascar and we propose that the Dipterocarpoideae proceeded from Africa to India while still linked to Madagascar. In addition, much subsequent diversification of this superclade has occurred on the Eurasian, Indian, SE Asian (Sunda) and North American plates post-Gondwanan breakup.This long vicariant history is supported by fossil, ecological, mycotrophic and morphological traits, and global circulation patterns that show negligible propensity for transoceanic dispersal to explain this clade’s wide intercontinental distribution.We conclude that all these areocladogram/plate-breakup/ ecomorphological/circulation features are consistent with a Gondwanan/early-Cretaceous (>115 Ma) origin for the Dipterocarpaceae-Cistaceae-Bixaceae superclade plus its three daughter clades. Future analyses at the species level, exploring alternative diversification dates from both fossils and plate-tectonic dynamics, are needed to refine these findings.