The evolution and diversification of ancient megathermal angiosperm lineages with Africa-India origins in Asian tropical forests is poorly understood because of the lack of reliable fossils. Our palaeobiogeographical analysis of pollen fossils from Africa and India combined with molecular data and fossil amber records suggest a tropical-African origin of Dipterocarpaceae during the mid-Cretaceous and its dispersal to India during the Late Maastrichtian and Paleocene, leading to range expansion of aseasonal dipterocarps on the Indian Plate. The India-Asia collision further facilitated the dispersal of dipterocarps from India to similar climatic zones in Southeast Asia, which supports their out-of-India migration. The dispersal pathway suggested for Dipterocarpaceae may provide a framework for an alternative biogeographic hypothesis for several megathermal angiosperm families that are presently widely distributed in Southeast Asia.
Many plant families lack substantive fossil records, limiting our understanding of their origin and evolution. The abundance and preservation potential of pollen through geological time have helped to overcome such limitations and have provided reliable fossils for reconstructing biogeographical history and character evolution in many angiosperm families. Here, using scanning electron microscopy, we identified six Ebenaceae-type fossil pollen grains from early Palaeogene sediments of western India. Phenetic and phylogenetic analyses using pollen characters of fossil and extant taxa reavealed affinities of these fossils to three genera of Ebenaceae (Euclea, Royena and Diospyros). Furthermore, our divergence dating analysis using these fossils as priors suggested a Gondwanan origin for the family during the mid-Cretaceous [c. 107 Mya, 95% highest posterior density (HPD): 100–112 Mya] and supports the boreotropical and ‘out of India’ dispersal hypotheses as the most probable explanations for the present global distribution of the family. The study also supports the dispersal of the family into India, from Africa, through the Kohistan–Ladakh Arc during the Palaeocene. Finally, comparative phylogenetic analyses suggest significant synapomorphic and phylogenetic signals for a few selected pollen characters in Ebenaceae. Our findings have important implications for understanding the biogeography and evolution of the highly diverse and ecologically and economically important family Ebenaceae.
Euphorbiaceae Juss. is a globally distributed angiosperm family with considerable diversity. It is divided into five subfamilies, each of which possesses pollen of distinct morphology. The subfamily Crotonoideae, occurring in evergreen, moist deciduous as well as dry deciduous forests of the world, shows a disjunct distribution pattern in Gondwana and Southeast Asia. This subfamily underwent multiple speciation and extinction events during the northward voyage of the Indian Plate during the Late Cretaceous-early Paleogene. We studied Crotonoideae fossil pollen from the Late Cretaceous Deccan Intertrappeans (Central India) and early Paleogene sediments from the western Indian lignite mines, and as a result, report 10 pollen fossils showing similarity with the extant genera Blachia, Croton, Endospermum, Jatropha, Klaineanthus, and Tetrorchidium, representing 4 tribes of Crotonoideae viz. Adenoclineae, Codiaeae, Crotoneae, and Jatropheae. Fossil evidences from the present study suggest a Gondwanan origin for Crotonoideae. Based on the extant and fossil species, Africa could be the place of origin for most of the Crotonoideae lineages that later dispersed to India via the Kohistan-Ladakh Island Arc during the late Maastrichtian-Paleocene time. The former distribution of Crotonoideae in mid-high latitudinal regions is due to the dispersal of the subfamily from Africa to mid latitudinal regions of northern hemisphere during the early Paleogene via the boreotropical dispersal route. This study also corroborates the "Out of India" hypothesis for the dispersal of Crotonoideae from India to Southeast Asia. The present deep-time fossil records from India discussed in this study substantiate the evolutionary and biogeographic history of subfamily Crotonoideae.
The Dipterocarpaceae plant family, that shows a disjunct distribution in Gondwanan continents and Southeast Asia, is a dominant constituent of the tropical rain forests of Southeast Asia. The high species diversity of Dipterocarpaceae in SE Asian rain forests suggests its origin from SE Asia. However, its fossil history is much younger, from Oligocene, from the region. Based on the pollen fossil records from the late Cretaceous-early Paleogene sedimentary sequences of Indian subcontinent and the contemporaneous distribution of its extant taxa, evolutionary history of Dipterocarpaceae has been traced. The study suggests a West Gondwanan origin for this family. Present study also provides first evidence of Dipterocarpaceae genus Vateriopsis (endemic in Seychelles) type fossil pollen record from the late Cretaceous and early Palaeogene sedimentary sequences of western Indian margin.
<p>Around 37% of the Mediterranean territory is covered with polyploid angiosperms, of which the genus <em>Linum</em> occupies a considerable region. <em>Linum </em>is the most diversified genus of the plant family Linaceae that comprises a &#8220;family pair&#8221; of Hugonioideae distributed in tropical regions and Linoideae mainly distributed in temperate to subtropical regions. We provide the oldest fossils of Linaceae, comparable to the living genera <em>Linum </em>and <em>Reinwardtia</em>, from the Late Cretaceous Infratrappean Deccan volcano sedimentary sequences of Maharashtra, India. The phylogenetic analysis conducted by combining the morphological characters of the pollen fossils recovered and the pollen morphological as well as molecular characters of extant species of Linaceae reveals that the family originated in the wet and warm tropical zones of South America in the Late Cretaceous. Thereafter, the family dispersed to Africa giving rise to the lineage of Linoideae that further diverged into two main clades, one of which evolved either on seasonally wet areas of Kohistan-Ladakh Island arc (KLIA) or on the Indian Plate in Maastrichtian-Paleocene. The second clade encompassing the genus <em>Linum </em>originated on seasonally wet areas of Africa and later dispersed to Mediterranean region via Boreotropical route in Paleocene where it adapted to seasonally dry climatic conditions that prevailed during late Eocene. The family further expanded its geographical range and spread to Eurasia, and to North America via Bering land bridge. We also propose the dual colonization of Linaceae<em> </em>in India. The seasonally wet lineages dispersed from Africa to India via KLIA in the Maastrichtian-Paleocene. Whereas, the seasonally dry lineages of <em>Linum </em>migrated from Eurasia into India probably during the Oligocene when the climatic conditions were dry and warm arid. The decline in global temperature towards the end of Eocene escalated the diversification rates within Linaceae that is currently found in the regions of meso- and microthermal climate. The next major shift in diversification rate was detected on the crown node of North American Linaceae during the Middle Miocene Climate Transition.</p>
Angiosperm evolved and diversified during Cretaceous. During this course of evolution and radiation, various pollen of uncertain origin had evolved. Aquilapollenites represents the early stock of angiosperms attaining its acme with respect to diversity and dominance during Campanian and Maastrichtian age. It was globally present (except Antarctica) however more dominant in northern hemisphere (Canada, North America, Sakhlain Oblast and China). In India, the Aquilapollenites sp. is present in Maastrichtian aged deposits. The pollen affinity has been associated with Loranthaceae and Santalaceae plant families. Here, a comparative description of all the Aquilapollenites sp. comprising a wide range of morphological diversity has been discussed. The wider morphological diversity and ecological adaptability of Aquilapollenites sp. infer that it is globally significant and warrants a more detailed study.
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