An overview of Palaeoenvironments and Palaeoclimates

Ecosystems of the recent past, all the way back to the formation of the Earth itself, can be reconstructed by means of palaeoenvironmental proxies. Fossil flora, fauna, and trace fossils can tell us about climate and biodiversity, which can be incorporated with sedimentology, geochemistry and palaeomagnetism. Together, these data allow palaeoecologists to build a detailed model of ancient ecosystems that can help us to understand why life on Earth evolved the way it did. What were the natural selective pressures driving evolution and what relationship do animals have to their environment? Answering these questions will aid in quantifying the current state of biodiversity and how destruction of habitats can impact on species loss.

The climate during the Miocene was similar to today's climate, but warmer. Well-defined climatic belts stretched from Pole to Equator, however, there were palm trees and alligators in England and Northern Europe. Australia was less arid than it is now. The past positions of the continents were incorporated with known distributions of rock types that form in specific climatic belts. Map by Christopher Scotese of the PALEOMAP Project with assistance from A. J. Boucot and Chen Xu.
The climate during the Miocene was similar to today’s climate, but warmer. Well-defined climatic belts stretched from Pole to Equator, however, there were palm trees and alligators in England and Northern Europe. Australia was less arid than it is now. The past positions of the continents were incorporated with known distributions of rock types that form in specific climatic belts. Map by Christopher Scotese of the PALEOMAP Project with assistance from A. J. Boucot and Chen Xu.

Palaeoenvironments as drivers of evolution

Organisms are dependent on their physical environment for survival, and factors such as changing climates, geography, fauna and vegetation all stimulate the evolution of unique adaptations by natural selection.

The Galápagos finches, made famous by Charles Darwin in his 1859 book On the Origin of Species, are a classic example of adaptive radiation among island populations.
The Galápagos finches, made famous by Charles Darwin in his 1859 book On the Origin of Species, are a classic example of adaptive radiation among island populations.

Many species of finches evolved from a common South American mainland ancestor, their beaks adapting to feed in different ecological niches on various islands in the Galápagos archipelago. Some finches have large, blunt beaks that can crack the hard shells of nuts and seeds. Other finches have long, thin beaks that can probe into cactus flowers without the bird being poked by the cactus spines. Still other finches have medium-size beaks that can catch and grasp insects. The physical environment of each island offered different food sources for exploitation as well as isolating its birds from other finch populations, preventing them from interbreeding and thus driving the evolution of new species.

Palaeoenvironmental reconstructions also provide the context for human morphological and behavioural evolution. Dietary preferences of the two-million-year-old hominin Australopithecus sediba from Malapa, South Africa were investigated using a combination of stable-isotope analysis, dental-microwear patterns and analysis of phytoliths extracted from dental calculus. Results show that Australopithecus sediba consumed a diet consisting mainly of tree leaves, fruits and bark, more similar to that of a chimpanzee than other contemporaneous australopiths in the region. Exploited food sources suggest that these hominins resided in a woodland environment.

Phytoliths are siliceous plant microfossils that often get trapped in plaque on teeth. The dental calculus of MH1 contained dicotyledon fruit phytoliths (a), dicotyledon wood or bark phytoliths (b), grass phytoliths (c) and sedge phytoliths (d). Images from Henry et al. (2012) and Darryl de Ruiter.
Phytoliths are siliceous plant microfossils that often get trapped in plaque on teeth. The dental calculus of MH1 contained dicotyledon fruit phytoliths (a), dicotyledon wood or bark phytoliths (b), grass phytoliths (c) and sedge phytoliths (d). Images from Henry et al. (2012) and Darryl de Ruiter.

Palynomorphs as a proxy for reconstructing palaeoenvironments

Fossil pollen and spores, acritarchs, and marine dinoflagellate cysts, chitonozoans and scolecodonts have much to tell us about past environments. Palynomorphs are present in sedimentary rocks from approximately two billion years ago to present, and in all sorts of environments. They represent parts of the life-cycles of plants and animals, which can be sensitive indicators of climate change, and as such palynology has great application for interpreting changing environments. In the Karoo Basin of South Africa, a climatic shift from glacial-type monosaccate pollen assemblages in the Late Carboniferous and Early Permian, to palynofloras dominated by taeniate bisaccate pollen in the Late Permian can be observed. As the climate became drier and more seasonal, taeniae on the main body of the pollen grain evolved as an adaptation to the swelling and contracting caused by considerable losses and gains of moisture in the environment.

Palynomorphs demonstrate climatic shifts from an icehouse to hothouse environment in the Karoo Basin. Original image by Rosemary Falcon (1986) redrawn by Natasha Barbolini.
Palynomorphs demonstrate climatic shifts from an icehouse to hothouse environment in the Karoo Basin. Original image by Rosemary Falcon (1986) redrawn by Natasha Barbolini.
Striatopodocarpites fusus, a taeniate bisaccate pollen grain common in Middle-Late Permian deposits of Gondwana. Image by Natasha Barbolini.
Striatopodocarpites fusus, a taeniate bisaccate pollen grain common in Middle-Late Permian deposits of Gondwana. Image by Natasha Barbolini.

Quantifying anthropogenic influence and the Sixth Mass Extinction

Ever-increasing human activity has transformed the planet, impacting on ecosystems, biodiversity, and species extinctions over the last 15 000 years. A key area of research is understanding when specific human activities, including hunting, land clearing and agriculture, began altering ecosystems at globally relevant scales. As such, the study of palaeoecology is very relevant to modern and future environments as well. Scientists have only been keeping detailed climatic records for a few decades, but much longer data sets are needed for accurate modelling in conservation ecology and projections of climate change. Palaeoecology can provide these critical data and improve our understanding of the Sixth Mass Extinction, which began with the disappearance of large mammals known as megafauna at the end of the last Ice Age, and continues today with plant and animal extinctions 100 – 10,000 times the natural rate. This is primarily caused by three factors: increased global concentration of greenhouse gases; oceanic devastation through overfishing and contamination; and the modification and destruction of huge areas of land and river systems to meet urban, industrial and agricultural needs.

Graph of CO2 (Green graph), temperature (Blue graph), and dust concentration (Red graph) measured from the Vostok, Antarctica ice core as reported by Petit et al. (1999). The graph shows that present-day levels of atmospheric CO2 are unprecedented over the past 420 thousand years, and that they are closely correlated to Antarctic temperature. Ice cores are one of the best palaeoenvironmental proxies available to scientists. Because the ice incorporates particles of dust, ash, pollen, atmospheric gas and radioactive substances, they can give information on temperature, ocean volume, precipitation, chemistry and gas composition of the lower atmosphere, volcanic eruptions, solar variability, sea-surface productivity, desert extent and forest fires stretching back 800 000 years.
Graph of CO2 (Green graph), temperature (Blue graph), and dust concentration (Red graph) measured from the Vostok, Antarctica ice core as reported by Petit et al. (1999). The graph shows that present-day levels of atmospheric CO2 are unprecedented over the past 420 thousand years, and that they are closely correlated to Antarctic temperature. Ice cores are one of the best palaeoenvironmental proxies available to scientists. Because the ice incorporates particles of dust, ash, pollen, atmospheric gas and radioactive substances, they can give information on temperature, ocean volume, precipitation, chemistry and gas composition of the lower atmosphere, volcanic eruptions, solar variability, sea-surface productivity, desert extent and forest fires stretching back 800 000 years.
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