Science - USA (2022-01-28)

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Asia

Africa

India

Kohistan-Ladakh

Island Arc (KLIA)

Antarctica

South

America

Australia

Madagascar

Late Cretaceous

~90 million years ago

Asia

Africa

India

Madagascar

KLIA

Late-Cretaceous–Paleogene

66 million years ago

Asia

Africa India

KLIA

Madagascar

Eocene

50 million years ago

However, one of the greatest challenges in

the field of paleobiogeography is the lack of

taxonomic resolution—in other words, the

precision of the fossil’s exact position on the

evolutionary tree. Recent developments in

optical techniques and machine learning ( 8 )

and the wider application of confocal laser

scanning microscopes, such as in the study

by Bansal et al., are overcoming this prob-

lem. With dipterocarps fossils classified into

clades, thanks to high-resolution microscopy,

the way is paved for more-refined biogeo-

graphic models for Dipterocarpaceae at large.

The closest sisters to the Asian diptero-

carps are the monotoid dipterocarps, belong-

ing to the subfamily Monotoideae, which are

distributed across South America, Africa,

and Madagascar. Going back a little more

on the family tree, one would find the fam-

ily Sarcolaenaceae, which is closely related

to all dipterocarps and is endemic to Mada-

gascar ( 4 ). Because of the apparent shared

genetic heritage among these tree species, an

African origin of the Asian dipterocarps has

been hypothesized before ( 1 , 7 ), but fossil evi-

dence for dipterocarps from Africa from the

Late Cretaceous to early Paleogene has been

scant. Most of the global dipterocarp record

in India and Africa is comparatively young,

but the newly discovered pollen fossils in In-

dia and Africa of various Asian dipterocarp

clades, together with the recent discovery of

Dipterocarpus leaves from India ( 9 ), push

back the age of the dipterocarps in India to

the Late Cretaceous.

The spatiotemporal context of these fos-

sils has biogeographic implications. One

hundred million years ago—when the dip-

terocarps originated—India would have

been too far south and too dry for diptero-

carps. However, 30 million years later, In-

dia advanced far enough north to host a

more tropical climate and more suitable

conditions for successful dipterocarp colo-

nization. Dispersal to India may have also

been promoted by the presence of island

arcs created by the subduction of the In-

dian tectonic plate under the Asian plate,

although the size and configuration of

these islands is still an open question.

Bansal et al. highlight the importance of

changes in climatic and geographic con-

nectivities for explaining biogeographic

distributions and diversity patterns today.

Had such paleogeographical and climatic

opportunities not presented themselves,

the flora of tropical Asia may well now

be quite different. Biotic invasions, such

as the Africa-to-Asia connection via India

( 10 ) or other continental landmasses, are a

recurring phenomenon in life’s history on

this planet. A similar example of intercon-

tinental dispersal was the Panama Isthmus,

which 15 Ma reconnected the Americas af-

ter a separation of more than 150 million

years. This prompted the Great Biotic In-

terchange of terrestrial organisms ( 11 ). But,

like all interchanges between two previ-

ously isolated landmasses, such exchanges

are usually asymmetric. For example, the

intrinsic characteristics of interacting bio-

tas may determine which species success-

fully invade the other biota and which do

not. The ability of dipterocarps to success-

fully colonize and eventually dominate

Asian forests may have depended on their

symbiotic relationships with root-associ-

ated fungi, which may have offered them a

competitive edge over the Asian plants that

were there before them ( 12 ).

The diaspora of the dipterocarps is not

unique and is mirrored in the history of

the Mauritiiinae palms, another native of

Africa that is now extremely successful in

South America ( 13 ). It is a strange twist of

fate that the African tropics, which con-

tributed to the diversity of both the Asian

tropics and the Neotropics, are now depau-

perate, partly because of the climate-driven

extinctions in Africa ( 14 ). The legacy of Af-

rica lives on and is a testament to the dy-

namic biophysical theater in which all life

on earth takes place; a legacy that will be

lost forever if concerted action is not taken

to preserve it. j

REFERENCES AND NOTES

1. P. S. Ashton, in Flora Malesiana, series I, Spermatophyta,
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2. A. Shenkin et al., Front. For. Glob. Change 2 , 32 (2019).


3. M. Bansal et al., Science 375 , 455 (2022).


4. J. Heckenhauer et al., Bot. J. Linn. Soc. 185 , 1 (2017).


5. M. J. Benton, P. Wilf, H. Sauquet, New Phytol. 10.1111/
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6. R. M. Kooyman et al., Annu. Rev. Ecol. Evol. Syst. 50 , 119
   (2019).


7. S. Klaus et al., Nat. Commun. 7 , 12132 (2016).


8. I. C. Romero et al., Proc. Natl. Acad. Sci. U.S.A. 117 , 28496
   (2020).


9. M. A. Khan et al., Plant Syst. Evol. 306 , 90 (2020).


10. R. M. Morley, J. Trop. Ecol. 34 , 209 (2018).


11. J. D. Carrillo et al., Proc. Natl. Acad. Sci. U.S.A. 117 , 26281
    (2020).


12. P. S. Ashton, Annu. Rev. Ecol. Syst. 19 , 347 (1988).


13. J. Y. Lim et al., Glob. Ecol. Biogeogr. 10.1111/geb.13436
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14. T. L. P. Couvreur et al., Biol. Rev. 96 , 16 (2021).


15. S. Chatterjee, A. Goswami, C. R. Scotese, Gondwana Res.
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ACKNOWLEDGMENTS

We thank C. Cannon, P. van Welzen, P. Roperch, and G. Dupont-

Nivet for discussions on dipterocarps and plate boundaries.

10.1126/science.abn6191

The dispersal of dipterocarps

Africa and India were once together as the megacontinent Gondwana. This landmass broke apart well before the origin of the dipterocarps (shown in the photo),

with Africa and India drifting apart ~150 million years ago ( 15 ). dProposed geographic range of dipterocarps

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