27 research outputs found
Early Cretaceous vegetation and climate change at high latitude: Palynological evidence from Isachsen Formation, Arctic Canada
Quantitative palynology of the marginal marine and deltaic-fluvial Isachsen Formation of the Sverdrup Basin, Canadian Arctic, provides insight into high latitude climate during much of the Early Cretaceous (Valanginian to early Aptian). Detrended Correspondence Analysis of main pollen and spore taxa is used to derive three ecological groupings influenced by moisture and disturbance based on the botanical affinities of palynomorphs: 1) a mixed coniferous assemblage containing both lowland and upland components; 2) a conifer-filicopsid community that likely grew in dynamic lowland habitats; and, 3) a mature dry lowland community composed of Cheirolepidiaceans. Stratigraphic changes in the relative abundance of pollen and spore taxa reflect climate variability in this polar region during the ~20 Mya history of the Isachsen Formation. The late Valanginian was relatively cool and moist and promoted lowland conifer-filicopsid communities. Warming in the Hauterivian resulted in the expansion coniferous communities in well-drained or arid hinterlands. A return to relatively cool and moist conditions in the Barremian resulted in the expansion of mixed lowland communities. This work demonstrates the utility of a multivariate statistical approach to palynology to provide insight into the composition and dynamics of ecosystems and climate of high latitude regions during the Early Cretaceous
Miocene palaeoclimate reconstructions from the North Alpine Foreland Basin in Germany
Early- and Middle-Miocene sediments of the North Alpine Foreland Basin (NAFB) in Southern Germany contain one of the world richest regional records of silicified wood. Here we analyze over 1,000 identifiable samples, belonging to 80 wood anatomical taxa from 61 stratigraphically well-dated localities using principally the Coexistence Approach. The samples investigated originate from fluvial sediments representing periods of intensified surface runoff in the NAFB and therefore represent and provide information pertaining to the wet end-member of the fluctuating climate system. The dry end of the climate system is represented in the profiles either by hiatuses or palaeosoils.
The dataset is split into four xylofloras: (I) the Ortenburg xyloflora (Late Ottnangian; ~17.5 to 17.3 Ma) originating from a paratropical evergreen Carapoxylon (Xylocarpus) forest; (II) the Southern Franconian Alb xyloflora (Late Karpatian; 17.0 to ~16.3 Ma) originating from a subtropical semideciduous limestone forest; (III) the upper Older Series xyloflora (Early Badenian; ~16.3 to ~15.3 Ma) originating from a subtropical oak-laurel forest; and (IV) the upper Middle Series xyloflora (Middle Badenian; 14.3 to ~13.8 Ma) originating from a subtropical dry deciduous forest
Taxodioxylon gypsaceum (Göppert) KrÀusel, legno fossile rinvenuto nel miocene dell'Italia centrale
Spiny plants, mammal browsers, and the origin of African savannas
Savannas first began to spread across Africa during the Miocene. A major hypothesis for
explaining this vegetation change is the increase in C4 grasses, promoting fire. We
investigated whether mammals could also have contributed to savanna expansion by using
spinescence as a marker of mammal herbivory. Looking at the present distribution of 1,852
tree species, we established that spinescence is mainly associated with two functional types of mammals: large browsers and medium-sized mixed feeders. Using a dated phylogeny for
the same tree species, we found that spinescence evolved at least 55 times. The
diversification of spiny plants occurred long after the evolution of Afrotherian
proboscideans and hyracoids. However, it is remarkably congruent with diversification of
bovids, the lineage including the antelope that predominantly browse these plants today.
Our findings suggest that herbivore-adapted savannas evolved several million years before
fire-maintained savannas and probably, in different environmental conditions. Spiny
savannas with abundant mammal herbivores occur in drier climates and on nutrient-rich
soils, whereas fire-maintained savannas occur in wetter climates on nutrient-poor soils.We thank the Government of Canada through Genome Canada and the
Ontario Genomics Institute (2008-OGI-ICI-03), the International Development Research
Centre (Canada), the University of Johannesburg Analytical Facility (South Africa), the South
African National Research Foundation, and the Royal Society (United Kingdom) for financial
support and various local and international authorities who granted plant collection
permits. T.C.-D., G.P.H., and W.J.B. thank the Mellon Foundation, the Claude Leon
Foundation, and the National Research Foundation for financial support.http://www.pnas.orghb2017Plant Scienc