May 25, 2021
Megafaunal Extinctions in South Asia
The megafaunal extinction is one of the one significant, and highly debated biotic crises of the last 100,000 years. Since the days of Darwin and Wallace, naturalists, paleontologists, and ecologists have documented the recent loss of large vertebrates around the world. Extinctions were most severe in the Americas, Australia, and on oceanic Islands, with a number of these land masses losing most vertebrates weighing over 50kg. However, there are exceptions: Africa and Southern Asia still have a diverse assemblage of large vertebrates that include elephants, rhinos, and big cats. Recent studies have documented a relatively limited extinction in parts of Africa, but until now, no one had systematically examined extinction dynamics in the Indian Subcontinent. Increasing evidence suggests that humans played a dominant role on a global scale, with their impacts being more severe in regions where Homo sapiens were the only species of hominin. Indeed, the survival of large vertebrates in Africa has been attributed to the co-evolution of these megafauna with multiple species of humans, but this hypothesis has yet to be tested anywhere outside the continent. India, bring at the crossroads of humans dispersal, with a long history of hominin occupation stretching 1.7 million years at least provides a tantalizing opportunity to study whether the length of human occupation results in low extinction magnitudes. In this presentation, I will briefly talk about the history of megafaunal studies in the Subcontinent, and then present data from research that I have conducted that documents the characteristics of the extinction of large vertebrates over the last 50,000 years.
Nuria Melisa Morales Garcia
University of Bristol
May 18, 2021
The feeding ecology of Mesozoic mammals: a biomechanical approach
The origin of mammals and most of their evolutionary history took place during the Mesozoic, so their study is of paramount importance. After teeth, jaws are one of the most common fossils of Mesozoic mammals: can the functional performance of Mesozoic mammal jaws reveal their diets? In this talk, I present the results stemming from my PhD thesis on the relationship between jaw functional performance and diet in small mammals, using a combination of geometric morphometrics and biomechanical techniques, including mechanical advantage and finite element analysis.
May 11, 2021
The Cyclostratigraphy Intercomparison Project (CIP) and the cyclostratigraphy.org website
Cyclostratigraphy is an important concept for understanding astronomical climate forcing and reading geological time in sedimentary sequences, provided that an imprint of insolation variations caused by Earth’s orbital eccentricity, obliquity and/or precession is preserved (Milankovitch forcing). In 2018, the Cyclostratigraphy Intercomparison Project (CIP) assessed the robustness of cyclostratigraphic methods using an experimental design of three artificial cyclostratigraphic case studies with known input parameters. This experiment demonstrated that cyclostratigraphy is a powerful tool for deciphering time in sedimentary successions and, importantly, that it is a trainable skill. The cyclostratigraphy.org website is the concrete translation of the lessons learned from CIP and its main purpose is to bring together and organize the cyclostratigraphic community. We want to do achieve this by offering high-quality learning materials in cyclostratigraphy, while also providing a platform where scientific results can be announced, and open questions can be discussed.
Florida Museum of Natural History
May 4, 2021
Paleoecological implications of non-lethal marginal traces in clypeasteroid echinoids
Non-lethal attacks by crustaceans and fish produce marginal traces on sand dollar (Echinoidea: Clypeasteroida) tests in modern environments. Marginal traces with comparable morphology are also observed in fossil specimens. These non-lethal marginal traces may provide quantifiable data on biotic interactions affecting both recent and fossil sand dollars, however, they are underexplored. We characterized non-lethal marginal traces on live-collected sand dollars from the northeastern Gulf of Mexico. The traces were cuspate in shape, healed, and located along the ambitus of the tests, rarely extending into the petals. Marginal traces comparable to the non-lethal traces documented in recent sand dollar specimens were also observed in post-Miocene fossil specimens from Florida reposited at the Invertebrate Paleontology Division at the Florida Museum. The characteristics of modern traces provide a protocol to identify non-lethal marginal traces on fossil sand dollars and help us better understand the evolutionary history of biotic interactions, specifically non-lethal attacks in the echinoid fossil record.
China University of Geosciences
April 27, 2021
Development and calibration of bacterial 3-hydroxy fatty acid based palaeoclimate proxies
Microbial lipids are sensitive to ambient environmental changes. To date, a number of organic geochemical proxies based on microbial lipids have been developed for palaeoclimate reconstruction. Gram-negative bacteria derived 3-hydroxy fatty acids (3-OH-FAs) have received recent attention for their potential as temperature and pH proxies. However, initial studies from altitudinal transects of contemporary soils – correlating bacterial 3-OH-FA compositions to air temperature and pH – have showed promising results, but also highlight regional differences in calibrations. Moreover, the distribution and performance of 3-OH-FA based proxies in lake and marine sediments remains largely unknown. This is a critical gap in knowledge as lake and marine sediments are the most common archives for palaeoclimate. Here we explore (including the application of machine learning tools) 3-OH-FAs distributions in 186 globally distributed soils to obtain global scale calibrations on temperature and pH proxies. We also investigate the applicability of 3-OH-FA based proxies in lacustrine and marine environments.
April 13, 2021
Evolution of temperature seasonality from the mid-Eocene to the early Oligocene, a model-data journey
Data and paleoclimate reconstructions allow us to describe better and better late Eocene to early Oligocene climate evolution, and the greenhouse-icehouse transition. However, we have learned mainly about the oceanic realms and terrestrial climate evolution remains poorly resolved. Some studies, mainly on paleobotanical remains, describe a stronger winter cooling through this period. This phenomena would have increased the Mean Annual Range of Temperatures (MATR), and thus result in a temperature seasonality strengthening. But, while it is described in large areas of the Northern Hemisphere, the mechanisms associated with seasonality increase have not been studied in depth.
In this study, we use different late Eocene to early Oligocene paleoclimate simulations (Earth System Model, IPSL-CM5A2) to trace the evolution of temperature seasonality patterns at a global scale and identify the respective contribution of three major forcing: pCO2 lowering, Antarctic ice-sheet formation, and the associated sea-level drop.
We show that the different forcing affect the MATR at zonal to regional scales. pCO2 drop produces large areas of MATR increase at high latitudes through sea-ice formation and albedo feedback. The Antarctic ice-sheet decreases seasonality of a large part of the Southern Hemisphere, but the sea level drop it brings creates multiple MATR increase zones by increasing continentality (coastal area expansion and sea retreat). Together these three forcing allow us to reconstruct seasonality change patterns in good agreement with data and the spatial heterogeneity they describe. The spatial distribution of increasing vs decreasing MATR zones appears partly correlated to that of the Eocene-Oligocene Transition biotic crisis, which calls for more in-depth studies of deep-time climate variability.
April 6, 2021
Dinosaurs and Decolonising Science Writing
South Africa has a rich collection of palaeontological finds but very rarely is the science behind it all explained in the almost 10 official indigenous languages in the country. By looking at how the science of dinosaurs is communicated, I investigate the history of colonialism and how science is taught and discussed in South Africa, and how journalists and researchers can use translation of science terms to creatively teach about science concepts that would be otherwise lost in inaccessible language.
Universidade Federal do Rio Grande do Norte
March 30, 2021
Between Bones, Footprints and Social Media
South America contains some of the last uncharted areas on this planet and holds a great deal of scientific potential in natural sciences. In this short talk, I will share with you the privilege of being an early-carrier paleontologist in Brazil and also some of its challenges. I have been for the past 15 years uncovering fossils from north to south in this country. The data I and my research group collected is contributing to the understanding of how local communities of dinosaurs and other organisms reacted to abrupt ecological changes during the breakup of the Gondwana. I will briefly share some of our finds with highlights in paleoichnology and paleohistology. Furthermore, since I strongly defend the Science cycle is never complete without dissemination, I’ll share some of the main strategies I’ve been using to talk with the public about our work and Paleontology in general. Considering Brazil is a country of high social contrasts and not everyone has access to quality education, science communication is an important tool for promoting inclusion.
University of Bergen
March 23, 2021 1500 UTC
Temperature controls carbon cycling and biological evolution in the ocean twilight zone
The ocean biological carbon pump, the process by which organic matter sinks from the surface to the deep ocean, may be sensitive to global temperature changes. Cooler ocean temperatures should slow respiration and the recycling of organic matter at the surface, increasing the efficiency of the biological pump in delivering organic matter at depth. Very efficient organic matter respiration and recycling at warm temperatures, would instead allow very little organic matter into the deep ocean. Here we test this hypothesis for the global cooling trend encompassing the last 15 m.yr. We use stable isotopes and the reconstructed depth distribution of planktonic foraminifera to investigate biological carbon pump processes at a global selection of sites. Middle Miocene to present-day climate and ocean conditions are simulated using an Earth System Model. Planktonic foraminiferal carbon isotope-depth gradients are compared with simulated carbon isotope profiles obtained using a temperature-dependent parameterization of the biological pump in the model ocean. We show that respiration rates slowed, and the efficiency of the biological pump increased with ocean cooling. In response, the mesopelagic “twilight zone” ecosystem expanded markedly and diversified as food penetrated deeper into the ocean interior.
University of California Santa Barbara
March 16, 2021
Investigating habitats and affinities of Neoproterozoic eukaryotes with single-fossil carbon isotope analysis
The evolutionary history of eukaryotes (organisms with a complex cell, including animals, plants, fungi) is long and considerably predates the first macroscopic life. The early eukaryotes are preserved in the rock record most commonly as organic-walled microfossils (OWM) and constitute the bulk of the Proterozoic fossil record. Single-celled eukaryotic fossils first appeared ~1650 Ma and diversified into crown-group lineages during the Neoproterozoic (1000-538 Ma), but little is known about their metabolisms, biological affinities, and habitats. It is unclear whether the early eukaryotes were restricted to oxygenated surface waters or refugia, or if they also inhabited the rest of the water column that was mostly anoxic ferruginous throughout Proterozoic. This information is critical to understand if and how different environmental conditions, e.g. stepwise ocean oxygenation during the Neoproterozoic, impacted eukaryotic evolution.OWM are found in shales deposited in anoxic and ferruginous bottom water, but thus far we couldn’t resolve what part of the water column they inhabited in life. Organic C-isotope analyses of individual microfossils can provide insight into short-term environmental variability and palaeoecology of early eukaryotes. We set out to explore whether different carbon pools influence OWM, with expectation that surface waters will contain heavier δ13C values due to export of light-C via photosynthesis. C-isotopic composition of individual bacterial and eukaryotic OWM was analysed, from shales of the Tonian (<782–729 Ma) Chuar Group in Arizona, USA using nano-EA-IRMS method for analysis of single microfossils. OWM show a wide spread of δ13C values per sample (-35.8 to -12.8‰, average -24‰), presumably incorporating carbon from heterogeneous sources. Mat-builder prokaryotic taxa are consistently depleted and lighter than the bulkrock δ13Corg, consistent with utilization of 13C-depleted carbon at depth, or DIC derived from respired planktonically-produced organic carbon. Some eukaryotic taxa like envelope-bearing Simia and acanthomorph Germinosphaera are enriched (c. -15‰). Simia has the broadest δ13C range in oxic samples, while it is enriched in anoxic ones, indicating it may have lived in surface waters. Other eukaryotes like Chuaria have depleted values, consistent with a benthic mode of life, and polyphyletic leiosphaerids have the broadest range of values per taxon. These results tentatively support habitat heterogeneity in the Chuar Group, and this approach may help us reconstruct early eukaryotic ecosystems.
University of Chicago
March 9, 2021
Whatcheeria and the ecomorphological disparity of early tetrapods
The early tetrapod Whatcheeria is represented by hundreds of specimens from the Mississippian (c.330 MYA) Delta locality (Iowa, USA). While “gratifyingly primitive” and having a consistent phylogenetic position on the tetrapod stem since its description in 1995, there have been a number of outstanding questions about its anatomy and especially its relationships. A variety of taxa and fossils from both the Devonian and Carboniferous have been termed ‘whatcheeriid’, but most of these assessments have not been based on comparison with Whatcheeria itself. There have also been hypotheses as to whether the whatcheeriids are a clade or just a grade of primitive Carboniferous or Devonian-Carboniferous tetrapods.
The large amount of Whatcheeria material permits a redescription the postcranial anatomy in detail and produce the first full-body reconstruction. Whatcheeria has robust limbs and girdles; in particular the humerus has large muscle attachments, implying a powerful retraction stroke. The structure of the forelimb and hindlimb suggest that they would have been well-suited to supporting the body, and in overall body proportions Whatcheeria resembles walking, terrestrially-adapted crown tetrapods from the Permian such as dissorophoids and diadectids. However, Whatcheeria retains a prominent lateral line system on the skull, and the wrist and ankles are primarily cartilaginous- indicators that it probably spent much of its time in the water. We interpret Whatcheeria as an underwater walking animal and propose that this locomotor mode was an important part of early tetrapod evolutionary ecology. This new data also allows for a revised diagnosis for a monophyletic Whatcheeriidae, and the exclusion of nearly all referred material. However, emerging phylogenetic results suggest that whatcheeriids may in fact have a Devonian origin.
Ohio State University
March 2, 2021
Barite and the marine barium cycle – from proxy records to models
The marine barium (Ba) cycle has been linked to the carbon cycle, and Ba-based proxies have been used in many studies to investigate carbon cycle dynamics. Barite (BaSO4) is a mineral that is a minor component of marine sediments and is used as a proxy for export production. A record of barite accumulation over the middle Miocene climate transition (~13.8 Ma) shows large variations in the carbon cycle with elevated export production that coincides with expansion of the Antarctic ice sheet and a carbon isotope excursion. Interpretations of Ba proxies can be complicated due to our limited knowledge of the processes that control marine Ba distribution. The marine Ba cycle has been modeled only as a simple two-box model. While box model approaches have provided valuable insight into some of the large-scale controls on the Ba cycle, they are not able to capture the spatial variability that is observed in the ocean Ba distribution. The Hamburg Oceanic Carbon Cycle Model Version 2.0 (HAMOCC 2.0) is expanded to include the marine Ba cycle. An initial control run shows general agreement between the modeled Ba distribution and that of the observed data. However, there are distinct differences in average Ba concentrations as well as distributions along equatorial belts and in the Arctic Ocean. Model optimization is ongoing, which will work to minimize differences between modeled and observed data.