Siwalik plant megafossil diversity in the Eastern Himalayas: A review

The Eastern Himalayas are renowned for their high plant diversity.To understand how this modern botanical richness formed,it is critical to investigate past plant biodiversity preserved as fossils throughout the eastern Himalayan Siwalik succession(middle Miocene-early Pleistocene).Here,we present a summary of plant diversity records that document Neogene floristic and climate changes.We do this by compiling published records of megafossil plant remains,because these offer better spatial and temporal resolution than do palynological records.Analyses of the Siwalik floral assemblages based on the distribution of the nearest living relative taxa suggest that a tropical wet evergreen forest was growing in a warm humid monsoonal climate at the deposition time.This qualitative interpretation is also corroborated by published CLAMP(Climate Leaf Analysis Multivariate Program) analyses.Here,we also reconstruct the climate by applying a new common proxy WorldClim2 calibration.This allows the detection of subtle climate differences between floral assemblages free of artefacts introduced by using different methodologies and climate calibrations.An analysis of the Siwalik floras indicates that there was a gradual change in floral composition.The lower Siwalik assemblages provide evidence of a predominance of evergreen elements.An increase in deciduous elements in the floral composition is noticed towards the close of the middle Siwalik and the beginning of the upper Siwalik formation.This change reflects a climatic difference between Miocene and Plio-Pleistocene times.This review helps us to understand under what paleoenvironmental conditions plant diversity occurred and evolved in the eastern Himalayas throughout the Cenozoic.

Coryphoid palms from the K-Pg boundary of central India and their biogeographical implications:Evidence from megafossil remains

Ten palm leaf impressions are documented from the latest Maastrichtian(late Cretaceous) to early Danian(earliest Paleocene) sediments(K-Pg,c.66-64 Ma) of the Mandla Lobe of the Deccan Intertrappean Beds,Madhya Pradesh,central India.The palmate leaf shape along with a definite wellpreserved costa support their placement in the subfamily Coryphoideae of the family Arecaceae.We place all recovered palm leaf specimens in the fossil genus Sabalites,report seven species of coryphoid palms and describe two new species namely,Sabalities umariaensis sp.nov.and Sabalites ghughuaensis sp.nov.The fossils indicate that coryphoid palms were highly diverse in central India by the latest Cretaceous.These and earlier reported coryphoid palm fossils from the same locality indicate that they experienced a warm and humid tropical environment during the time of deposition.These discoveries confirm the presence of a diversity of Coryphoideae in Gondwana prior to the India-Eurasia collision and provide information about coryphoid biogeographical history over geological time.Based on megafossil remains,we trace coryphoid palm migration pathways from India to mainland Southeast(SE) Asia and other parts of Asia after the docking of the Indian subcontinent with Eurasia early in the Paleogene.

Evidence of the oldest extant vascular plant(horsetails)from the Indian Cenozoic

Equisetum(Equisetaceae)has long been a focus of attention for botanists and palaeontologists because,given its extensive and well-documented fossil record,it is considered the oldest extant vascular plant and a key element in understanding vascular plant evolution.However,to date,no authentic fossil evidence of Equisetum has been found from the Indian Cenozoic.Here,we describe a new fossil species,namely,E.siwalikum sp.nov.,recovered from the middle Siwalik(Late Miocene)sediments of Himachal Pradesh,western Himalaya.We identified fossil specimens based on morphological and epidermal characters.In addition,X-Ray diffraction(XRD)analysis was used to determine the mineral composition of compressed stems of Equisetum.The close affinity of our recovered Siwalik fossils to Equisetum is supported by the presence of both macromorphological and epidermal characters.Because Equisetum generally grows in wet conditions around water reservoirs,our findings indicate that the fossil locality was humid and surrounded by swamp and lowland regions during deposition.Ample fossil evidence indicates that this sphenopsid once existed in the western Himalaya during the Siwalik period.However,at present Equisetum is confined to a particular area of our fossil locality,probably a consequence of severe environmental changes coupled with competition from opportunistic angiosperms.Our discovery of Equisetum fossils in appreciable numbers from the Siwalik sediments of the Himachal Himalayas is unique and constitutes the first reliable recognition of Equisetum from the Indian Cenozoic.

Earliest megafossils of scandent calamoid palms from the Deccan Intertrappean Beds of Central India and their paleobiogeographic implications

Two well-preserved petrified palm stems from the latest Maastrichtian(Late Cretaceous) to earliest Danian(Early Paleocene) sediments of the Deccan Intertrappean Beds of Madhya Pradesh, Central India are described. Their significant anatomical characteristics include a Calamus-type general stem pattern,the presence of well-preserved fibrovascular bundles(fvbs) with two wide metaxylem vessel elements(230 μm-250 μm) and one phloem strand, uniform density of fvbs, lack of continuity between protoxylem and metaxylem vessel elements, and an absence of centrifugal differentiation of sclerenchymatous fibrous parts.These features reveal a close resemblance to those of extant genera of scandent Calamoideae. The permineralized stems are described as a new species namely, Palmoxylon calamoides Kumar, Roy et Khan sp. nov.The fossils represent the oldest reliable fossil records of this family, supporting their Gondwanan origin, their importance in tracing their migration pathways from India to Europe and other continents after the docking of the Indian subcontinent with Eurasia during the Paleocene, and an “Out-of-India” dispersal hypothesis. Today the subfamily Calamoideae is disjunctly occurred in Africa, Asia, Australia, Europe, and South America, but the poor deep-time fossil record of this subfamily with a small number of Cenozoic fossils makes hypotheses concerning its origin and dispersal difficult to evaluate. The present study has significant implications for the origin and migration of this subfamily and the paleoclimate.

Occurrence of Persea Mill. from the Siwalik Forest of Darjeeling, Eastern Himalaya： Paleoclimatic and Paleogeographic Implications

Fossil leaf remains of two new species of Persea Mill., belonging to the family Lauraceae collected from the lower part of the Siwalik sediments（Gish Clay Formation of Sevok Group, Middle Miocene） of Darjeeling foothills of eastern Himalaya, are described. The new species are Persea miogamblei sp. nov. and Persea neovillosa sp. nov.. On the basis of leaf architecture（size, shape and venation pattern） fossil leaves described in this article closely resemble modern leaves of Persea gamblei（King ex Hook. f.） Kosterm. and Persea villosa（Roxb.） Kosterm.. The geographic distribution of the fossils and their modern counterparts are discussed and on that basis tropical evergreen vegetation with a warm and humid climate at the time of deposition of the Siwalik sediments is suggested in contrast to the present day tropical deciduous vegetation in this area. The present finding also suggests probable migration of these lauraceous taxa to Southeast Asia.