TY - JOUR

T1 - Northward expansion of the southern-temperate podocarp forest during the early Eocene

T2 - Palynological evidence from the NE Tibetan Plateau (China)

AU - Robin-Champigneul, Faez

AU - Gravendyck, Julia

AU - Huang, Huasheng

AU - Woutersen, Amber

AU - Pocknall, David

AU - Meijer, Niels

AU - Dupont-Nivet, G.

AU - Erkens, Roy H.J.

AU - Hoorn, C.

N1 - Funding Information: We are grateful to the Botanical Garden in Bonn and its gardeners facilitating access to the living collection of podocarps for photographic documentation, and Naturalis Biodiversity Center for providing microscopic slides on loan. We further thank Helma Kuijpers and Kèvin Knoops of the Microscopy CORE lab (University of Maastricht) for their support with confocal microscopy. We are very grateful to Christiane Wenske and Ulrich Heimhofer (Leibniz University Hannover) who provided access to lab and microscope equipment. We thank Rudolf Bauerfeind (Medizinische Hochschule Hannover) and Ingrid Romero for their insightful support with Airyscan microscopy. and Yaron Malkowsky (University of Bonn) for his support with scanning electron microscopy (SEM). GDN, NM, and AW acknowledge consolidator grant Monsoons in Asia caused Greenhouse to Icehouse Cooling (MAGIC) 649081 JG acknowledges funding for SEM work from the Deutsche Forschungsgemeinschaft (DFG), project nr. 471591895. Finally, we thank the anonymous reviewer for their valuable feedback.

PY - 2023/9

Y1 - 2023/9

N2 - The debated vegetation response to climate change can be investigated through palynological fossil records from past extreme climate conditions. In this context, the early Eocene (53.3 to 41.2 million years ago (Ma)) is often referred to as a model for a greenhouse Earth. In the Xining Basin, situated on the North-eastern Tibetan Plateau (NETP), this time interval is represented by an extensive and well-dated sedimentary sequence of evaporites and red mudstones. Here we focus on the palynological record of the Early Eocene Climatic Optimum (EECO; 53.3 to 49.1 Ma) and study the fossil gymnosperm pollen composition in these sediments. In addition, we also investigate the nearest living relatives (NLR) or botanical affinity of these genera and the paleobiogeographic implications of their occurrence in the Eocene of the NETP. To reach our objective, we complemented transmitted light microscopy with laser scanning- and electron microscopy techniques, to produce high-resolution images, and illustrate the morphological variation within fossil and extant gymnosperm pollen. Furthermore, a morphometric analysis was carried out to investigate the infra- and intrageneric variation of these and related taxa. To place the data in context we produced paleobiogeographic maps for Phyllocladidites and for other Podocarpaceae, based on data from a global fossil pollen data base, and compare these with modern records from GBIF. We also assessed the climatic envelope of the NLR. Our analyses confirm the presence of Phyllocladidites (NLR Phyllocladus, Podocarpaceae) and Podocarpidites (NLR Podocarpus, Podocarpaceae) in the EECO deposits in the Xining Basin. In addition, a comparative study based on literature suggests that Parcisporites is likely a younger synonym of Phyllocladidites. Our findings further suggest that the Phyllocladidites specimens are derived from a lineage that was much more diverse than previously thought, and which had a much larger biogeographical distribution during the EECO than at present. Based on the climatic envelope of the NLR, we suggest that the paleoclimatic conditions in the Xining Basin were warmer and more humid during the EECO. We conclude that phylloclade-type conifers typical of the southern-temperate podocarp forests, had a northward geographical expansion during the EECO, followed by extirpation.

AB - The debated vegetation response to climate change can be investigated through palynological fossil records from past extreme climate conditions. In this context, the early Eocene (53.3 to 41.2 million years ago (Ma)) is often referred to as a model for a greenhouse Earth. In the Xining Basin, situated on the North-eastern Tibetan Plateau (NETP), this time interval is represented by an extensive and well-dated sedimentary sequence of evaporites and red mudstones. Here we focus on the palynological record of the Early Eocene Climatic Optimum (EECO; 53.3 to 49.1 Ma) and study the fossil gymnosperm pollen composition in these sediments. In addition, we also investigate the nearest living relatives (NLR) or botanical affinity of these genera and the paleobiogeographic implications of their occurrence in the Eocene of the NETP. To reach our objective, we complemented transmitted light microscopy with laser scanning- and electron microscopy techniques, to produce high-resolution images, and illustrate the morphological variation within fossil and extant gymnosperm pollen. Furthermore, a morphometric analysis was carried out to investigate the infra- and intrageneric variation of these and related taxa. To place the data in context we produced paleobiogeographic maps for Phyllocladidites and for other Podocarpaceae, based on data from a global fossil pollen data base, and compare these with modern records from GBIF. We also assessed the climatic envelope of the NLR. Our analyses confirm the presence of Phyllocladidites (NLR Phyllocladus, Podocarpaceae) and Podocarpidites (NLR Podocarpus, Podocarpaceae) in the EECO deposits in the Xining Basin. In addition, a comparative study based on literature suggests that Parcisporites is likely a younger synonym of Phyllocladidites. Our findings further suggest that the Phyllocladidites specimens are derived from a lineage that was much more diverse than previously thought, and which had a much larger biogeographical distribution during the EECO than at present. Based on the climatic envelope of the NLR, we suggest that the paleoclimatic conditions in the Xining Basin were warmer and more humid during the EECO. We conclude that phylloclade-type conifers typical of the southern-temperate podocarp forests, had a northward geographical expansion during the EECO, followed by extirpation.

KW - Hyperthermal

KW - Morphometry

KW - Palaeobiogeography

KW - Palaeoclimate

KW - Phyllocladus

KW - Podocarpaceae

UR - http://www.scopus.com/inward/record.url?scp=85163858419&partnerID=8YFLogxK

U2 - 10.1016/j.revpalbo.2023.104914

DO - 10.1016/j.revpalbo.2023.104914

M3 - Article

AN - SCOPUS:85163858419

VL - 316

JO - Review of Palaeobotany and Palynology

JF - Review of Palaeobotany and Palynology

SN - 0034-6667

M1 - 104914

ER -