Surprisingly modern Latest Cretaceous– earliest Paleocene woods of India

Abstract

Background and approach – The Deccan Intertrappean Beds of Central India contain a diverse assemblage of fossil plants, including petrified woods from 15 localities. These beds are dated at c. 67–64 Ma, i.e. latest Cretaceous–earliest Paleocene and span the K-Pg boundary, a significant time in angiosperm history. At this time, the Indian tectonic plate was halfway on its journey from Gondwana to its collision with Asia, and relatively close to the equator. We provide descriptions in IAWA Hardwood List codes for 47 species of Deccan fossil woods, based on our examination of thin sections of these woods, mostly holotypes that are housed at the Birbal Sahni Institute of Palaeobotany, Lucknow, India. An appendix lists all validly published Deccan wood species of which we are aware, including 52 that we were not able to examine. Main results – The Deccan fossil woods described herein include the oldest known occurrences of some orders, families or genera viz. Lamiales (Lamia-ceae), Achariaceae (Hydnocarpus-like wood), Anacardiaceae, Simaroubaceae (Ailanthus-like and Simarouba-like woods), subfamily Leeoideae (Vitaceae), subfamily Myrtoideae (Myrtaceae), subfamily Planchoideae (Lecythidaceae), tribe Castilleae (Moraceae), tribes Grewioideae and Sterculioideae (Malvaceae). These first fossil records are discussed with reference to other macrofossil and pollen records of the same or related clades. They complement recent work on the oldest known Olea and Connaraceae also documented by Deccan woods.For the Deccan woods we examined, we could confirm the earlier taxonomic assignment at least down to order or family level for 29 taxa. Ordinal level affinities are ambiguous for eight of the taxa. In two cases, we revised the taxonomic assignment to other families; for another eight, the original assignment was found to be incorrect, but we are unable to suggest alternative affinities. Evolutionary implications – Only 3% of all Deccan woods have scalariform perforations and the incidences of so-called specialized features in the Baileyan sense are high, so these woods have a remarkably “modern” aspect. This is anomalous in comparison with contemporaneous fossil woods from higher paleolatitudes, and seemingly they are more “derived” than the recent flora. In these respects, the Deccan woods constitute a unique assemblage. The low incidence of scalariform perforations suggests xeric conditions, while – in contrast – the low incidence of distinct growth ring boundaries suggests an aseasonal everwet climate. It is speculated that convergent xylem specialization, especially the selection for simple perforations, was enhanced by the climatic conditions found at low paleolatitudes with high temperatures as would characterize the Deccan Intertrappean Beds at the K-Pg boundary.

Faunal elements from the Deccan volcano‐sedimentary sequences of India: A reappraisal of biostratigraphic, palaeoecologic, and palaeobiogeographic aspects

“…Detailed studies on the anatomical features of the silicified woods (mainly from the Mandla sub‐province) suggest prevalence of a mesic, subtropical to tropical climate during the deposition of the DVSS in the sub‐province (Smith et al, ). These inferences were also supported subsequently by Wheeler, Srivastava, Manchester, and Baas (), who carried out a detailed examination of thin sections of >40 species of permineralized wood specimens belonging to families, viz., Anacardiaceae, Achariaceae, Lamiales (Lamiaceae), Simaroubaceae; subfamilies, viz., Planchoideae (Lecythidaceae), Leeoideae (Vitaceae), and Myrtoideae (Myrtaceae); and tribes, viz., Grewioideae, Sterculioideae (Malvaceae), and Castilleae (Moraceae).…”

“…Although the above palaeobiogeographic aspects mainly take into account the faunal elements, it is important to mention that permineralized megafloral remains (e.g., seeds, fruits, flowers, and wood) from the DVSS (e.g., Mandla sub‐province) have also been utilized in a palaeobiogeographic context (Srivastava, ; Wheeler et al, and references therein). Manchester et al () recorded the globally oldest permineralized remains belonging to family Vitacea from the Maastrichtian Mohgaon‐Kalan and adjoining sections.…”

More Malpighiales: Woods of Achariaceae and/or Salicaceae from the Deccan Intertrappean beds, India

“…The present fossil woods are much better preserved than earlier fossils ascribed to Hydnocarpoxylon , clearly showing vessel‐ray pits, septate fibres and other details. Conspecificity with Hydnocarpoxylon indicum is indicated, described by Bande & Khatri () from Parapani and critically revisited by Wheeler et al (). This species has been recorded from many Deccan Intertrappean localities (Guleria & Mehrotra, ; Guleria & Srivastava, ) and also from Neogene sediments of Kerala (Awasthi & Srivastava, ).…”

“…The very “modern” aspect of the Deccan wood flora suggests that tropical climatic conditions may have accelerated adaptive xylem evolution (simple perforation plates) to fit the high demands for hydraulic efficiency typical for tropical lowland forests (Baas et al, ). This paper on Deccan Malpighiales, along with other recent contributions, (Srivastava et al, –Oleoxylon ; Baas et al, –Connaroxylon ; Shukla & Mehrotra, – Duabangoxylon ; Wheeler et al, –47 taxa) expands our knowledge of the species‐rich Deccan fossil flora from a crucial epoch in the evolution of the angiosperms.…”

Ecological and Biogeographic Implications of Asian Cenozoic Fossil Floras

“…Srivastava et al () augment their earlier review of numerous latest Cretaceous to Paleocene dicotyledonous woods of the Deccan Intertrappean beds of India (Wheeler et al, ) with renewed attention to representatives of the Parietal Clade of the Malpighiales. Based on wood anatomical characters, they recognize two new representatives: Elioxylon of uncertain modern affinities, and Hydnocarpoxylon indicum Bande & Khatri resembling modern Hydnocarpus Gaertn.…”