Gabi Serrato Marks
September 22, 2020
New speleothem-derived insights into northern Mexican paleoclimate during the first millennium of the Common Era
There were major population centers in northern Mexico, including the city of Teotihuacan, that experienced dramatic shifts during the first millennium of the Common Era (CE), but we lack precisely dated and high resolution paleoclimate records to investigate the climate events under which these civilizations survived or collapsed. I will present a precisely dated speleothem from San Luis Potosí, Mexico (289 ± 13 to 976 ± 29 CE) as a new record of hydroclimatic change. We used stable isotopes and trace metal to calcium ratios to identify several shifts toward drier conditions, indicating the presence of multidecadal droughts.
Postdoc, Rutgers University
September 15, 2020
Intermixed Messages: geochemical and paleontological records of the end-Devonian Hangenberg Crisis in the Appalachian Basin, USA
The end-Devonian Hangenberg Crisis constituted one of the greatest ecological and environmental perturbations of the Paleozoic Era. While this biocrisis is considered a global event, its cause and overarching effects remain uncertain, especially within the Appalachian Basin of the United States. We integrate geochemical and paleontological records to characterize the onset and paleoenvironmental transitions associated with the Hangenberg Crisis within the Cleveland Shale member of the Ohio Shale. Organic geochemical proxies such as lipid biomarker analysis and stable isotopes allow us to probe the dynamics of the microbial communities that drove Devonian biogeochemical cycles before, during, and after the extinction event. Results indicate that much of the end-Devonian water column was euxinic (anoxic with free hydrogen sulfide). Regardless of this ubiquitous euxinic signal, there is an overprinted record of bioturbation, or the traces of past burrowing organisms, which suggests that the seafloor was not continuously devoid of life. Despite highly variable water column and sedimentary redox conditions, as well as the extinction known to be occurring in macrofaunal clades, lipid biomarker evidence shows that there is little to no change in the microbial communities that drive the base of the food chain at any point during this biotic crisis.
Emanuela di Martino
Postdoc, University of Oslo
September 8, 2020
A walk through the fascinating world of BRYOZOANS: what can they tell us about the past?
In my research, I use fossil bryozoans as a model system to answer paleobiological and macroevolutionary questions.
Bryozoans are a phylum of invertebrate, aquatic, colonial animals which made their first appearance in the Ordovician and are still successfully colonizing the oceans today.
Although bryozoans were the subject of Charles Darwin’s first scientific paper, at that time they were classified as zoophytes because of their puzzling attributes seemingly somewhere between animals and plants. Even today they are very little known among non-specialists.
Nonetheless, calcified bryozoans provide an optimal model system in studies of biodiversity, paleoecology and evolution for several reasons. They are major components of the marine benthos in both modern and ancient oceans. They are distributed globally in a wide range of habitats and at all depths. They have diagenetically resistant and typically well-preserved skeletons. Their skeletal complexity provides a wealth of characters for a rigorous species-level taxonomy. Furthermore, their skeletal morphology directly reflects life history variation and ecological function, a rarity in the fossil record.
In this talk, I will show examples of what bryozoans can tell us about the past. These include studies from my previous and current research projects in:
i) Biodiversity: I used extensive paleontological collections of Caribbean and Indonesian bryozoans to address the timing of the divergence in species richness between the two regions and to evaluate the relative contributions of differential rates of origination and extinction to the diversity patterns we observe today.
ii) Paleoecology: As the majority of bryozoans live as encrusters of hard substrates such as rocks and shells, substrate availability is a prime factor controlling their distribution, often leading to competition for space among colonies or other organisms. These competitive interactions entail skeletal overgrowths which can be preserved in the fossil record, offering one of the few systems in which to study directly competition and its consequences in the geological past.
iii) Macroevolution: Capitalizing on the polymorphic nature of bryozoans and the separation between feeding and reproductive individuals within colonies, we can tackle the outstanding problem of using the fossil record to estimate trait-fitness associations for phenotypic traits, and ask if such associations are consistent with macroevolutionary patterns of the same phenotypes.
PhD Student, University of Kansas
September 1, 2020
Out of the dark: The mysterious origins and rapid diversification of bats
Bats are the second most species-rich group of living mammals, with over 1400 species currently known. The earliest fossil bats date to ~55 Ma, and new species of Eocene bats continue to be named from localities around the world. Despite their living and fossil diversity, the evolutionary origins and biogeographic history of bats remain effectively unknown. Fossil bats appear nearly simultaneously on continents as distant as Australia and Europe, and no transitional bat fossils are currently recognized. Because the fossil record of bats is acknowledged to be poor compared to that of other mammals, creative methods must be employed to understand the origins and biogeography of the order. I present ongoing work describing some of the earliest known bat fossils, with implications for understanding the paleoecology and region of origin of Eocene bats. I also discuss challenges and approaches for understanding the potential outgroups of bats in the Paleocene.
Postdoc, The Open University
August 25, 2020
EARNEST: Examining the Agroforestry Landscape Resilience in INdia to inform Social-Ecological Sustainability in the Tropics
The effective management of human-dominated tropical forest landscapes is crucial in the wake of global climate change affecting biodiversity, ecosystem functions, and the livelihoods of billions. Among varied land management practices in the tropics, agroforestry remains one of the most promising, promoting deliberate maintenance of trees on farmlands, facilitating avenues for mitigating climate change and enhancing ecosystem functions. Considering these merits, the Indian Government launched the National Agroforestry Policy (NAP) in 2014, world’s first, nationwide policy with a core idea of increasing the agroforestry area concurrent with the expansion of national forest cover. As one of world’s most populous countries and its fastest growing economies, moving towards “Green India” would be a serious game-changer for this tropical country with positive global environmental implications. The effective implementation of this economically valuable policy falls on the shoulders of Indian Forest Departments (IFDs), who uphold a strict policy of preventing fires in and around forests. Fire is an integral part of forest ecosystem functioning and its strict prevention-suppression could be detrimental to biodiversity. While this scientific evidence emerged from palaeoecology has led to comprehensive fire management and conservation plans in some parts of the world, there is currently a shortfall of evidence-based policymaking in human-dominated tropical landscapes. The disagreement in fire practices in India often instigate serious conflicts between IFDs and local communities that traditionally use fires, hampering implementation and the desired impact of the NAP. In this context, harnessing fossil pollen-based diversity indices (e.g., pollen richness and evenness, and temporal β-diversity), past fire management, the intervals of increased aridity, and land use history, EARNEST examines the synergistic impacts of anthropogenic fires and aridity on local plant diversity in the rainforests of Western Ghats of India, one of world’s biodiversity hotspots supporting the highest population density. By developing a historical perspective, EARNEST deepens fundamental knowledge of tropical agroforestry landscapes and tackles a crucial aspect of the effectiveness of fires in managing these landscapes. It actively resources new knowledge towards designing efficient biodiversity conservation and fire management strategies in the Western Ghats and wet tropics at large. The key message from EARNEST is that for the success of environmental management in any tropical region, it is important to recognise that people are part of the landscape. Fire management and conservation frameworks in the face of future monsoon variability can only be effective if they are planned in tandem with careful incorporation of evidence-based traditional land management approaches.
Project “EARNEST” has received funding from the European Union’s Horizon 2020 research and innovation programme under the grant agreement no. 795557.
Postdoc, University of Bristol
August 18, 2020
Extending CO2 estimates in the geologic record using a chlorophyll-based CO2 proxy
As the concentration of atmospheric carbon dioxide (pCO2) continues to rise along with the increasing demands from our growing population, we need to understand the precise relationship between pCO2 and climate (aka climate sensitivity) to brace for the future. Over the past one million years, pCO2 has shown a striking relationship with temperature, as recorded in air bubbles trapped in ice cores. However, beyond the one-million-year ice core record, we must rely on proxies to reconstruct pCO2, i.e. physically preserved material which reflect an environmental parameter. Developing and calibrating proxies remains a challenge, with different proxies suggesting different values throughout time. To provide geologic context for climate sensitivity, we need to better constrain proxy uncertainty.
Here, we apply this proxy over the mid-Miocene Climatic Optimum (16.9 to 14.7 Ma) for several reasons: 1. It may be an analogue for the near future, 2. It seems to behave differently than other climates in time, and 3. It has highly varied pCO2 estimates during this time. We use a refreshed approach to reconstruct pCO2 from the stable carbon isotopic fractionation that occurs during photosynthesis. Possibly providing a more universal pCO2 proxy (both in time and location) in the geologic record, we develop and test the potential of the organic geochemical compounds that are many by most phytoplankton: phytane, a degradation product of the vital pigment chlorophyll that can be found in all photoautotrophs e.g. plants and algae and cholestane, a degradation product of cholesterol found in all (and only) eukaryotes. This refreshed approach, combined with global temperatures, is used to calculate climate sensitivity. We find that this period is not in fact exceptional and its climate sensitivity is firmly within the standard IPCC estimates, thus resolving the enigma of the warm mid-Miocene.
PhD Student, Indian Institute of Science Education and Research
August 11, 2020
Role of Late Quaternary climate and vegetation composition in the evolution of prehistoric humans in India
The Quaternary is known as “Age of Humans” because of the presence of abundant fossil record of Homo species in the geological records. The period has witnessed extraordinary changes in global climate, which resulted in the extinction of many mammalian species and must have controlled or contributed to the evolution of Homo species. Although the fossil records of early Homo species are absent from the Indian subcontinent, varieties of stone tools unearthed from sedimentary deposits of the Quaternary age suggest the presence of tool-making prehistoric humans on the landscape. Based on the study of excavated artefacts and their morphology, it has been suggested that the prehistoric humans of the Indian subcontinent were using the Paleolithic to Neolithic tools. The age of the prehistoric phase varies from global to regional scale and remains a matter of inquisitiveness. Therefore, it is required to have complete control over the age of prehistoric phases before understanding the role of climate on the Homo evolution.
In this direction, we selected the fluvial sections of the Belan valley situated in north-central India that preserved the signature of prehistoric human settlement from Paleolithic (~100 ka) to Neolithic (~3 ka) interval. For the first time, we conducted analyses of oxygen and carbon isotopes in soil carbonates (δ18OSC and δ13CSC) and compound-specific hydrogen and carbon isotopes in leaf wax n-alkanes (δDC29 andδ13CC29) of paleosol from six archaeological sites to understand the climate-cultural relationship. The results suggest several phases of intensified monsoonal rainfall punctuated by drier episodes, which also partly controlled the vegetation composition in the last ~100 ka. Our study reveals the role of climate and vegetation in controlling the prehistoric population or local migration during the Middle Paleolithic to Early Neolithic phase.
Postdoc, La Brea Tar Pits & Museum
August 4, 2000
Ancient Originations, Recent Extinctions: Fossil Insights on Extant Carnivore Biodiversity
How ecological traits influence organismal success is a recurring question in paleobiology, particularly as specialization toward extremes may act differently at various scales: traits benefitting an individual may disadvantage its population, species or clade. For example, the ecological specializations of large body size and hypercarnivory (diet over 70% meat) have evolved repeatedly in mammals; yet large hypercarnivores are thought to be trapped in a macroevolutionary “ratchet”, marching unilaterally toward extinction. I examined the relationship between specialization and success over the past 40 million years in North American canids (dogs), a group with considerable ecomorphological disparity and a dense fossil record. Across all canids, a nonlinear relationship emerged between species duration and carnivory: species on either end of the carnivory spectrum tend to have shorter durations than middling species. In two of three canid subfamilies, large-hypercarnivore diversification appears constrained at the clade level, biasing specialized lineages to extinction. However, despite these shorter durations and elevated clade extinction, large hypercarnivores were not disadvantaged at the species level for most of canid history. Extinction was size- and carnivory-selective only at the Pleistocene-Holocene boundary 11,000 years ago, when large-scale biotic and abiotic impacts precipitated the rise of modern carnivore communities primarily comprising fewer predators and smaller species. This trophic and body-size downgrading has continued at the microevolutionary level, producing ecomorphological shifts perceptible in carnivoran species surviving to the modern-day.
Postdoc, University of Birmingham
July 28, 2020
Decoding Deep Time Diversity: Physical, Human & Environmental Drivers of Diversity in the Fossil Record
The fossil record is our window into past worlds and provides critical insights into organisms’ responses to past environmental change. Yet, the fossil record is notoriously incomplete and uneven, impacting our ability to interpret the true drivers of biodiversity patterns in deep time. In this talk, Emma will draw on her own research into Palaeozoic and Mesozoic tetrapods (four-limbed beasties) to explore the various physical (geological) and human factors that bias the fossil record, as well as quantitative ways these biases can be mitigated in order to reveal ‘true’ patterns of past diversity. With these biases revealed, she will then explore the environmental changes that drove tetrapod diversity during two key periods of their evolution: first, the emergence of vertebrate life onto land in the late Palaeozoic, and finally, the establishment of modern ecosystems and rise of dinosaurs during the early Mesozoic.
Postdoc, Stanford University
July 21, 2020
Alternating Macroevolutionary Regimes in Phanerozoic Marine Animal Body Size
Extinction selectivity is key in predicting which groups of organisms are likely to die out during a major extinction event. This predictive power of extinction assumes that extinction selectivity does not change from background intervals during mass extinction events. The traits that enhanced the chances of survival of taxa during background intervals, however, have at times failed to protect them during a mass extinction event, as the rules of macroevolution changed. In other words, a mass extinction can represent a switch to a distinct macroevolutionary regime from background processes. Moreover, this idea of alternating macroevolutionary regimes between background processes and mass extinctions is not limited to just extinction; origination dynamics are equally important to long-term evolutionary outcomes of pre- and post-mass extinction events. Thus, testing between these possibilities is a fundamental challenge with possible profound implications not only for understanding the origins of the modern biosphere but also for predicting the consequences of the current biodiversity crisis. The evolution of animal body size represents an ideal metric with which to test for the alternation of macroevolutionary regimes, as it scales with important aspects of organismal biology. Using a dataset of marine genera with body size data ranging from the Early Ordovician through Pleistocene, we test for the alternation of macroevolutionary regimes between background intervals and the “Big Five” mass extinction events using capture-mark-recapture approaches. We find that differences between background and mass extinction are more pronounced for origination than for extinction. Thus, the differences in macroevolutionary regimes between background and mass extinctions may be more pronounced during recovery intervals than during mass extinction events themselves.
Omar Rafael Regalado Fernandez
PhD, University College London
July 14, 2020
What’s in a name? Reconstructing the evolutionary history of the transition from ‘prosauropods’ to sauropods
The sauropod body plan is very clear and simple to identify among dinosaur lineages, with columnar arms, straight gaits, long necks and tails, and rarely small legs. The sauropod body plan is the last to emerge in the sauropod lineage where the body dimensions spanned three orders of magnitude and the locomotion varied from bipedal to quadrupedal; these non-sauropod sauropods are often referred to as ‘core prosauropods.’ The sauropod form seems to be established by the Late Triassic, with a trend to greater form sizes, quadrupeds and reduced chewing apparatus. It has been proposed that the sauropod bauplan evolved gradually from prosauropods through paedomorphosis, where the initiation of sexual maturity occurs at a younger age, making it possible for adults to maintain their juvenile characteristics. Several characters have been attributed to originate this way, such as skull morphology and quadrupedity. Nevertheless, after every character published in the literature has been reassessed some elements of this scenario of gradual evolution could be an artefact from character coding. After a thorough reanalysis of the anatomy of this group, several lines of evidence suggest that Sauropodomorpha has undergone a disparification event, where several lines have developed several feeding strategies and locomotion types. The classical ‘prosauropods’ are better understood as a few smaller clades, suggesting the coexistence of several body plans diversifying before the partition of Pangaea in the Early Jurassic. Additionally, a biotic turnover of the flora during the Triassic-Jurassic transition suggests that more generalist feeding behaviours replaced the specialist herbivores of the Late Triassic.
Postdoc, Oxford University
July 7, 2020
The origin of herbivory in tetrapods: the founding of modern ecosystems
The origin of herbivory in tetrapods (limbed vertebrates) was a crucial event in the establishment of terrestrial vertebrate ecosystems. By allowing access to the vast resource represented by plants, it led to considerable changes in patterns of trophic interactions on land. This ultimately gave rise to the first modern style of terrestrial ecosystems, where large numbers of vertebrate herbivores support a relatively small number of top carnivores, during the late Paleozoic.
Terrestrial floras appear to have been “architecturally” modern by the end of the Devonian, with lignified forests, a shrubby understory and a diverse array of herbaceous plants. However, the evolution of terrestrial herbivorous animals lagged considerably behind this and until the late Carboniferous almost all primary consumers in these ecosystems were detritivorous invertebrates. Even following the first appearance of high-fibre herbivorous tetrapods, these remain rare relative to large macro-predators. Instead, there was a greater link between terrestrial and aquatic ecosystems, with a diverse array of amphibians moving primary productivity from water to support large carnivores. It wasn’t until the Middle Permian crash in amphibian diversity and abundance that more modern terrestrial ecosystems appeared. The establishment of these ecosystems directly impacted on plant evolution. At the local scale the appearance of tetrapod herbivores constrained plant diversity throughout the Permian. This constraint, coinciding with the appearance of smaller, more selective hebivores, is consistent with patterns observed in modern terrestrial ecosystems. This provides an illustration of the potential for fossil data to test predictions of ecological interactions first observed in extant ecosystems.
PhD, Penn State
June 30, 2020
Size and shape variation in the calcareous nannoplankton genus Braarudosphaera following the Cretaceous-Paleogene (K-Pg) mass extinction: clues as to its evolutionary success
Calcareous nannoplankton (which includes the coccolithophores), have been dominant primary producers in the surface oceans since the late Triassic. The largest mass extinction event in their evolutionary history occurred following the bolide impact at the Cretaceous-Paleogene (K-Pg) boundary ~66.0 Ma, which led to the elimination of over 90% of nannoplankton species. One of the only surviving genera of the K-Pg mass extinction was Braarudosphaera: a nannolith family which unlike the coccolithophores precipitates pentagonal calcite plates (pentaliths). B. bigelowii, the only species of Braarudosphaera to span the K-Pg boundary, is still present (albeit rare) in the modern ocean and forms geographically and temporally restricted blooms throughout geologic time, including in the earliest Paleocene. Morphometric and molecular data indicate that at least four genetically distinct B. bigelowii morphotypes are present in the modern ocean. At present, it is uncertain whether these morphotypes have disparate eco-physiological tolerances that have allowed them to readily adapt to varying environmental conditions. For the first time, we assess changes in both the size and shape of Braarudosphaera pentaliths following the K-Pg mass extinction event at three sites with early Paleocene Braarudosphaera blooms [the Chicxulub impact crater (Mexico), Brazos River (USA), and Agost (Spain)]. Using these data, we assess the role of morphotypic variation within the highly unstable post-impact environment in a range of different marine settings. Our results show that disparate Braarudosphaera morphotypes were dominant in the Gulf of Mexico compared to the paleo-Tethys, likely due to regional environmental differences. In addition, we provide evidence that the dominant Braarudosphaera morphotypes shifted, and that new forms evolved, in response to both local and global environmental change. This ability to rapidly adapt to unstable environments likely helped Braarudosphaera survive the K-Pg extinction, and explains why this lineage has enjoyed such a long evolutionary history.
Postdoc, Rutgers University
June 23, 2020
The Seawater Carbon Inventory at the Paleocene-Eocene Thermal Maximum
56 million years ago, the Earth underwent a rapid climate change event called the “Paleocene-Eocene Thermal Maximum” (PETM). Sedimentary records show that a massive amount of carbon was released into the atmosphere, causing ocean acidification, warming, and a widespread extinction of deep-sea organisms. To help quantify ocean acidification at the PETM, we are using the boron content (the B/Ca ratio) of the shells of fossilized foraminifera as a proxy for past ocean pH and carbon content. I will present new calibrations for the B/Ca proxy that we have created by growing living planktic foraminifera in seawater chemistry analogous to that of the Paleogene and simulating severe ocean acidification. Using our new calibrations, I will show that the B/Ca proxy supports the theory that volcanic carbon emissions were a major driver of PETM warming.