Dipterocarpus Gaertn. (Dipterocarpaceae) leaf from the Middle Siwalik of eastern Nepal and its phytogeographic and climatic significance

Srivastava, Gaurav; Adhikari, Purushottam; Mehrotra, R. C.; Paudel, Lalu Prasad; Uhl, Dieter; Paudayal, Khum N.

doi:10.3126/jngs.v53i0.23799

Cited by 10 publications

(10 citation statements)

References 14 publications

(17 reference statements)

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“…Dipterocarpus leaf fossils are most convincing when the typical architecture of straight, regular, robust secondaries and opposite percurrent tertiary veins (features found in several plant groups) are combined with the taxonomically restricted feature of visible plications, as seen in our fossils and several previous examples ( Kräusel, 1929a ; Srivastava et al, 2017 ). Khan et al (2020) recently assigned leaf fossils to Dipterocarpus from Deccan sediments, close to the Cretaceous-Paleogene boundary in Madhya Pradesh, central India, and considered these specimens as evidence for the popular out-of-India model for the introduction of Dipterocarpoideae into Asia ( e.g ., Dutta et al, 2011 ).…”

Section: Discussionsupporting

confidence: 70%

First fossil-leaf floras from Brunei Darussalam show dipterocarp dominance in Borneo by the Pliocene

Wilf

Zou

Donovan

et al. 2022

PeerJ

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The Malay Archipelago is one of the most biodiverse regions on Earth, but it suffers high extinction risks due to severe anthropogenic pressures. Paleobotanical knowledge provides baselines for the conservation of living analogs and improved understanding of vegetation, biogeography, and paleoenvironments through time. The Malesian bioregion is well studied palynologically, but there have been very few investigations of Cenozoic paleobotany (plant macrofossils) in a century or more. We report the first paleobotanical survey of Brunei Darussalam, a sultanate on the north coast of Borneo that still preserves the majority of its extraordinarily diverse, old-growth tropical rainforests. We discovered abundant compression floras dominated by angiosperm leaves at two sites of probable Pliocene age: Berakas Beach, in the Liang Formation, and Kampong Lugu, in an undescribed stratigraphic unit. Both sites also yielded rich palynofloral assemblages from the macrofossil-bearing beds, indicating lowland fern-dominated swamp (Berakas Beach) and mangrove swamp (Kampong Lugu) depositional environments. Fern spores from at least nine families dominate both palynological assemblages, along with abundant fungal and freshwater algal remains, rare marine microplankton, at least four mangrove genera, and a diverse rainforest tree and liana contribution (at least 19 families) with scarce pollen of Dipterocarpaceae, today’s dominant regional life form. Compressed leaves and rare reproductive material represent influx to the depocenters from the adjacent coastal rainforests. Although only about 40% of specimens preserve informative details, we can distinguish 23 leaf and two reproductive morphotypes among the two sites. Dipterocarps are by far the most abundant group in both compression assemblages, providing rare, localized evidence for dipterocarp-dominated lowland rainforests in the Malay Archipelago before the Pleistocene. The dipterocarp fossils include winged Shorea fruits, at least two species of plicate Dipterocarpus leaves, and very common Dryobalanops leaves. We attribute additional leaf taxa to Rhamnaceae (Ziziphus), Melastomataceae, and Araceae (Rhaphidophora), all rare or new fossil records for the region. The dipterocarp leaf dominance contrasts sharply with the family’s <1% representation in the palynofloras from the same strata. This result directly demonstrates that dipterocarp pollen is prone to strong taphonomic filtering and underscores the importance of macrofossils for quantifying the timing of the dipterocarps’ rise to dominance in the region. Our work shows that complex coastal rainforests dominated by dipterocarps, adjacent to swamps and mangroves and otherwise similar to modern ecosystems, have existed in Borneo for at least 4–5 million years. Our findings add historical impetus for the conservation of these gravely imperiled and extremely biodiverse ecosystems.

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Section: Discussionsupporting

confidence: 70%

First fossil-leaf floras from Brunei Darussalam show dipterocarp dominance in Borneo by the Pliocene

Wilf

Zou

Donovan

et al. 2022

PeerJ

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“…This is perhaps best illustrated by the Namling flora ( Guo et al., 2019 ). Even without quantitative paleoaltimetry it is obvious that floras such as that found at Namling are distinctly different from contemporaneous floras from the Siwaliks that exhibit much greater diversity and contain numerous taxa typical of tropical vegetation ( Srivastava et al., 2017 , Srivastava et al., 2018a , Srivastava et al, 2018 ) as well as remains of thermophilic animals ( Gilbert et al., 2017 ; Kundal et al., 2017 ; Sankhyan and Èeròanský, 2016 ; Sankhyan et al., 2017 ; Sankhyan and Chavasseau, 2018 ).…”

Section: An Overview Of the Cenozoic Biota Of The Tibetan Regionmentioning

confidence: 99%

Cenozoic topography, monsoons and biodiversity conservation within the Tibetan Region: An evolving story

Spicer

Farnsworth

2020

Plant Diversity

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The biodiversity of the Himalaya, Hengduan Mountains and Tibet, here collectively termed the Tibetan Region, is exceptional in a global context. To contextualize and understand the origins of this biotic richness, and its conservation value, we examine recent fossil finds and review progress in understanding the orogeny of the Tibetan Region. We examine the deep-time origins of monsoons affecting Asia, climate variation over different timescales, and the establishment of environmental niche heterogeneity linked to topographic development. The origins of the modern biodiversity were established in the Eocene, concurrent with the formation of pronounced topographic relief across the Tibetan Region. High (>4 km) mountains to the north and south of what is now the Tibetan Plateau bounded a Paleogene central lowland (<2.5 km) hosting moist subtropical vegetation influenced by an intensifying monsoon. In mid Miocene times, before the Himalaya reached their current elevation, sediment infilling and compressional tectonics raised the floor of the central valley to above 3000 m, but central Tibet was still moist enough, and low enough, to host a warm temperate angiosperm-dominated woodland. After 15 Ma, global cooling, the further rise of central Tibet, and the rain shadow cast by the growing Himalaya, progressively led to more open, herb-rich vegetation as the modern high plateau formed with its cool, dry climate. In the moist monsoonal Hengduan Mountains, high and spatially extensive since the Eocene but subsequently deeply dissected by river incision, Neogene cooling depressed the tree line, compressed altitudinal zonation, and created strong environmental heterogeneity. This served as a cradle for the then newly-evolving alpine biota and favoured diversity within more thermophilic vegetation at lower elevations. This diversity has survived through a combination of minimal Quaternary glaciation, and complex relief-related environmental niche heterogeneity. The great antiquity and diversity of the Tibetan Region biota argues for its conservation, and the importance of that biota is demonstrated through our insights into its long temporal gestation provided by fossil archives and information written in surviving genomes. These data sources are worthy of conservation in their own right, but for the living biotic inventory we need to ask what it is we want to conserve. Is it 1) individual taxa for their intrinsic properties, 2) their services in functioning ecosystems, or 3) their capacity to generate future new biodiversity? If 2 or 3 are our goal then landscape conservation at scale is required, and not just seed banks or botanical/zoological gardens.

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“…Since 2016, a considerable amount of work has been done on the qualitative as well as quantitative reconstruction of palaeoclimate by using plant fossils collected from the eastern, central and western part of the Himalaya (Adhikari et al 2018;Srivastava et al, 2017Srivastava et al, , 2018. Studies on phytogeographic aspects have also been undertaken.…”

Section: Fossil Floras and Paleoclimatesmentioning

confidence: 99%

“…Paleobotanical investigations carried out by Srivastava et al (2017Srivastava et al ( , 2018 ) for Temperature of the Coldest Month (CMT), and ~5.4 °C (calculated using averages) for Mean Annual Range of Temperature (MART). The reconstructed CIs of the precipitation are: 1748-2869 mm (average ~2308.5 mm) for Mean Annual Precipitation (MAP), 300-329 mm for MPwet (average ~314.5 mm), 46-135 mm for MP dry (average ~90.5 mm), 128-221 mm for MPwarm (average ~174.5) and ~224 mm (calculated using averages) for Mean Annual Range of Precipitation (MARP).…”

Section: Fossil Floras and Paleoclimatesmentioning

confidence: 99%

Himalayan Cenozoic biotas and climate: an overview of recent advances

Bajpai¹,

Singh²,

Patnaik³

et al. 2020

PINSA

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The early Cenozoic was a turning point in the geological history of the Indian subcontinent as it was during this interval that the Indian plate collided with Asia, leading to profound changes in global climates, faunal and floral evolution, orogeny and oceanography. Later Cenozoic records include those from the well known Siwalik successions which continue to yield important data relevant to age refinements of critical horizons including those yielding fossil hominoids, as well as for our understanding of the influence of climate change on the evolution of a diverse group of vertebrates including mammals. Studies on Himalayan Neogene floras have yielded phytogeographically important data as well as valuable insights in to paleotemperature and paleoprecipitation regimes. This report presents an overview of important recent contributions on the fossil fauna and flora, paleoenvironments and paleoclimates from the Himalayan Cenozoic sedimentary sequences.

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Dipterocarpus Gaertn. (Dipterocarpaceae) leaf from the Middle Siwalik of eastern Nepal and its phytogeographic and climatic significance

Cited by 10 publications

References 14 publications

First fossil-leaf floras from Brunei Darussalam show dipterocarp dominance in Borneo by the Pliocene

First fossil-leaf floras from Brunei Darussalam show dipterocarp dominance in Borneo by the Pliocene

Cenozoic topography, monsoons and biodiversity conservation within the Tibetan Region: An evolving story

Himalayan Cenozoic biotas and climate: an overview of recent advances

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