Browsing by Subject "Miocene"

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  • Loponen, Laura (Helsingin yliopisto, 2020)
    The Miocene epoch (c. 23-5 million years ago) was a noteworthy geological time period in which significant changes took place both in the climate regimes as well as in vegetation characteristics, bringing about novel adaptations in many herbivorous lineages. These adaptations constituted morphological, dietary, and ecological factors in a relatively short period of evolutionary time. Among these herbivores were the proboscideans, the living and extinct elephants, which were among the most dominant and largest herbivores at the time. Despite that proboscideans were diverse and large group of hundreds of species, yet the understanding of dietary and ecological patterns of majority of Miocene sympatric species is still limited. The aim of this study was to analyse the molar surfaces of Miocene proboscideans (e.g. Deinotherium and Gomphotherium) from Eurasia to provide a reconstruction of the feeding preferences of the study species based on observed dental wear. The dental wear indicates the abrasiveness of the diet, thus allowing broad categorization to either browser (<10% grass in the diet), mixed-feeder (10-90% grass in the diet) or grazer (>90% grass in the diet). Secondly, this study aimed for providing estimation of the environmental characteristic and vegetation patterns of the study localities by comparing to the previous studies and to hypsodonty value (proxy of general openness and aridity of the environment). Proboscidean dietary signals from the key localities of Maragheh (Iran) and Pannonian basin (Austria) were compared with the paleobotanical studies. Thus, the general estimation of spatial and temporal variation of the environment characteristics in the study localities were based on these parameters. The materials of fossilized molars were analysed by mesowear angle method, in which the measured angles show the diet abrasiveness due the nutritional targets’ differences. The results allowed the reconstruction of the feeding preferences which suggested that majority of Miocene proboscideans were browsers and browse-dominated mixed feeders or pure mixed-feeders. Instead, Choerolophodon pentelici was found grass-dominant mixed-feeder. The wide spectrum of feeding preferences allowed diet flexibility according available vegetation and also these sympatric species to co-exist by niche partitioning. Thus, demonstrating clearly the connection between diets and environments thought the diet. As a conclusion, in the diet of the paleocommunities of proboscideans had, on average, more grass-dominant components in open and dry environment likely due the presence of grass-dominant vegetation. Instead, in the wet conditions the closed-canopy forest environments enhanced browsing. Further, the results indicated shift in feeding preferences of proboscideans prior to Miocene climate and environment changes. These results are in line with the findings of the previous studies of modern elephants’ diet- environment relationships. The further studies would provide insight to the relative amounts of the grass in the diet of Miocene proboscideans.
  • Junna, Tuomas (Helsingin yliopisto, 2020)
    Pedogenic ferromanganese nodules and concretions are prevalent redoximorphic features in tropical and sub-tropical soils. The nodules are typically highly enriched in Fe and Mn that are present as oxides, hydroxides and oxyhydroxides. The formation of nodules happens via precipitation and translocation of metals as the soil redox state undergoes cyclical changes between reductive and oxidizing settings. As the nodule elemental distribution and structure is primarily and expression of the prevailing soil redox conditions, Fe-Mn nodules have the potential to be a useful tool of paleoclimatological analysis. The Chinese Loess Plateau (CLP) is a terrestrial archive for study of changes in the monsoon climate system. During Late Miocene, the intensification of the Asian Monsoon system caused an increase in warmth and humidity in inland Eastern Asia during a global trend of increased aridity and decreasing temperatures. Fe-Mn nodules from three different soil horizons, formed 8.07, 7.7 and 3.7 Ma ago in Lantian, southern CLP, were studied to compare nodules from varying sedimentary settings formed under different moisture regimes. Using electron microscopy methods, the structure and elemental distribution of nodules were described to compare their redoximorphic features. Large Fe-Mn nodules from floodplain sediments (8.07 Ma) show a well-developed structure, high metal enrichment and signs of variations in rate of formation and dominant redox states. The soil redox conditions are likely primarily controlled by the river flooding. Nodules from two eolian deposits (7.7 Ma and 3.7 Ma) were, on average smaller and showed less metal enrichment, less elemental differentiation and less variance in the dominant redox conditions. Only small, poorly developed nodules were found from older eolian sediments whereas younger soil horizon contained larger nodules with evidence of higher hydromorphism. While potential for using the nodules from eolian sediments to assess changes in precipitation exists, the lack of paleoclimatological information in smaller nodules, the small sample count, limitations of the methods and variance in depositional settings increase the uncertainty of the interpretation.
  • Halali, Sridhar; van Bergen, Erik; Breuker, Casper J.; Brakefield, Paul M.; Brattstrom, Oskar (2021)
    New ecological niches that may arise due to climate change can trigger diversification, but their colonisation often requires adaptations in a suite of life-history traits. We test this hypothesis in species-rich Mycalesina butterflies that have undergone parallel radiations in Africa, Asia, and Madagascar. First, our ancestral state reconstruction of habitat preference, using c. 85% of extant species, revealed that early forest-linked lineages began to invade seasonal savannahs during the late Miocene-Pliocene. Second, rearing replicate pairs of forest and savannah species from the African and Malagasy radiation in a common garden experiment, and utilising published data from the Asian radiation, demonstrated that savannah species consistently develop faster, have smaller bodies, higher fecundity with an earlier investment in reproduction, and reduced longevity, compared to forest species across all three radiations. We argue that time-constraints for reproduction favoured the evolution of a faster pace-of-life in savannah species that facilitated their persistence in seasonal habitats.