Karma Nanglu
Postdoc, Smithsonian NMNH
January 19, 2021
Worms from the rocks: Burgess Shale fossils shed light on old mysteries
The Cambrian Explosion, marking the rapid first appearance of most major animal groups in the fossil record, is one of the most important biological events to have ever occurred. There is no better place to get a window into this over half-a-billion-year-old event than the Burgess Shale, a fossil site in the Canadian Rockies that has provided unique insights into the origins of animal life for over 100 years. One notable exception to this rule has been the early evolution of the marine worms known as hemichordates, which have historically had a poor fossil record. In this talk, I’ll guide you through a series of recent studies using Burgess Shale fossils that shine a light on hemichordate origins, one of the most mysterious parts of the animal tree of life. These exceptional fossils reveal unanticipated combinations of morphological and ecological characteristics early in the history of this animal group, including surprising combinations of those found in their modern relatives.
Nussaibah Raja
PhD Student, Friedrich-Alexander-Universität Erlangen-Nürnberg
December 8, 2020
The dirty truth: scientific colonialism in palaeontology
Analyses of past global biodiversity are severely hindered by sampling biases and gaps in the fossil record, previously been attributed to several geological and biological factors. However, global compilations of fossil occurrences not only reflect the physical aspects of the fossil record, but also document the historical compilation of this data over more than two centuries. This shows who has influence on the fossil data collection, access and availability by determining who has access to specimens and the ability to do research.
Natalie Umling
Postdoc, American Museum of Natural History
December 1, 2020
All the single forams: should we put a ring on area density?
Paleo-proxies of past atmospheric CO2 have demonstrated that continued unabated anthropogenic emissions could result in CO2 levels not documented since the Eocene period, 55 million years ago (Foster et al., 2017). However, many atmospheric CO2 paleo-proxies have large errors or are temporally and spatially limited. The area density proxy of foraminiferal shell thickness and calcification intensity has the potential to provide information about past ocean-atmosphere CO2 exchange and has the benefit of small sample requirements, simple analytical techniques, and the ability to re-use the analyzed foraminifera for other paleo-proxies. Some initial evaluation of this proxy has been done using ‘pristine’ foraminifera from sediment traps and plankton tows (Marshall et al., 2013; Osborne et al., 2016; Weinkauf et al., 2016) and through evaluation of cultured foraminifera (Davis et al., 2017; Henehan et al., 2017). Because foraminifera preserved in marine sediments can rarely be considered ‘pristine,’ we have to account for the additional influences associated with marine sediment burial and diagenesis before this proxy can be applied back in time. Using a series of multi-core core-tops collected from the southeastern Indian Ocean, we evaluate the reliability of utilizing sediment core Globigerina bulloides area density values to estimate surface ocean carbonate parameters. We find that confining area density measurements to a narrow range of values can account for influences related to cryptic speciation and shell preservation, up to a maximum area density value at which diagenesis begins to overprint the surface ocean signature. We investigate the relationship of surface ocean temperatures, carbonate ion concentrations, and phosphate concentrations with our newly defined G. bulloides area density ranges. Our developed calibrations indicate a relative insensitivity of G. bulloides area density to seawater properties, limiting their utility for reconstructing past surface ocean carbonate ion variability. Nevertheless, reconstructing the distribution of area density values in a given sample has the potential to provide valuable information on overall sample preservation as a shift in the distribution of the sample population from more well-preserved, lower area density shells to more poorly preserved, higher area density shells.
Emma Karoune
Postdoc
November 24, 2020
Open Science Practices in Phytolith Research and Beyond
Open science is becoming an integral part of all scientific research but the extent of these practices in many fields is unknown, including phytolith research. I will present the findings of my recent project concerning the assessment of open science practices in phytolith research. My research assessed data and metadata sharing, and open access, in a sample of journal articles containing primary phytolith data from 16 prominent archaeological and palaeoecological journals (341 articles). It builds on similar studies conducted for archaeological science (Marwick & Pilaar Birch 2018) and macro-botanical remains (Lodwick 2019). I collected data concerning data format, reusability of data, inclusion of phytolith morphotype pictures for identification purposes and a fully described method, use of the International code for phytolith nomenclature (ICPN) and whether the articles were open access. I will suggest steps forward to use as a starting point for discussions in the wider phytolith and academic communities to develop guidelines for greater integration of open science practices and discuss how a move to a more holistic open approach will produce a more sustainable future for our research.
Kaustubh Thirumalai
Assistant Professor, University of Arizona
November 17, 2020
Methane, Monsoons, and Modulation of Millennial-scale Variability
Earth’s orbital geometry exerts a profound influence on climate by regulating changes in incoming solar radiation. Superimposed on orbitally paced climate change, Pleistocene records reveal substantial millennial-scale variability characterized by abrupt changes and rapid swings. However, the extent to which orbital forcing modulates the amplitude and timing of these millennial variations is unclear. Here we isolate the magnitude of millennial-scale variability (MMV) in two well-dated records, both linked to precession cycles (19,000- and 23,000-year periodicity): composite Chinese speleothem δ¹⁸O, commonly interpreted as a proxy for Asian monsoon intensity, and atmospheric methane. At the millennial timescale (1,000–10,000 years), we find a fundamental decoupling wherein precession directly modulates the MMV of methane but not that of speleothem δ¹⁸O, which is shown to be strikingly similar to the MMV of Antarctic ice core δ²H. One explanation is that the MMV of methane responds to changes in midlatitude to high-latitude insolation, whereas speleothem δ¹⁸O is modulated by internal climate feedbacks.
Thomas Clements
Leverhulme Early Career Fellow, University of Birmingham
November 10, 2020
All fossils are rotten: understanding decay is key to understanding exceptionally preserved fossils
The fossil record is our only ‘window’ into the evolution of animals and plants throughout geological history. Unfortunately, this window is murky, because nature favours obliteration of organic material – predominately through decay – which acts to remove information from the fossil record. Of course, organics do preserve, and these are usually tissues that have a high preservation potential (are more decay-resistant) such as biomineralised tissues (bones, teeth, shells etc.) which explains their dominance in the fossil record. There are, however, processes in certain depositional environments that allow an organism’s soft-tissues to enter the inorganic lithosphere. These soft-tissue fossils are important as they allow more accurate reconstructions of ancient ecosystems and because they retain vital anatomical information which can be used to investigate animal evolution, especially during pivotal periods of Earth’s history, like the Cambrian Explosion. The science of taphonomy seeks to understand the processes that control preservation of organics, from the immediate moments after death and subsequent burial (biostratinomy), mineralisation, diageneses, and geological processes. My talk will introduce experimental taphonomy and will showcase my work trying to understand three tiers of taphonomic bias: 1) preservational potential of different tissue types within an organism, 2) varying preservational potential of related organisms and 3) the impact of paleogeography on soft-tissue preservation.
Esther Githumbi
Postdoc, Lund University
November 3, 2020
Quantitative pollen-based vegetation reconstructions
Understanding land use and land cover (LULC) change through time is an important aspect when attempting to interpret human-environment interactions through time. Palaeoenvironmental techniques have been crucial in bridging this gap by providing information that has been used to estimate climate change, vegetation change, sea level change etc. through time using a variety of proxies. Producing quantitative land-cover reconstructions has been an aim and a challenge with several methods attempted during the decades. In LandClimII (Land and Climate interactions in Europe during the Holocene project, we use the REVEALS model, which has been tested and validated, in several regions of the world. REVEALS is a Landscape Reconstruction Algorithm model that estimates vegetation abundance/plant cover at the regional scale (100 km x 100 km). The LRA is the most widely tested, validated, and applied pollen-based quantitative reconstruction approach to date.
Jamie McFarlin
Postdoctoral Associate/INSTAAR Affiliate, University of Colorado Boulder
October 27, 2020
Recent advances in using the hydrogen and oxygen isotopes of biomarkers in Arctic lake sediments to reconstruct precipitation isotopes
Global climate models project that over the coming century precipitation patterns will change as temperatures rise. Environmental and social structures are sensitive to regional changes in the hydrologic cycle and more extreme expressions of precipitation (e.g. droughts, flooding) will have far reaching consequences. Predicting local-to-regional scale changes is thus important for helping communities prepare for and navigate a new normal. Geologic records of past climate provide insight into how the climate system responded during periods warmer-than-present. However, precipitation remains a difficult climate variable to reconstruct. The goals of this talk are to provide a broad overview of recent advances in using the hydrogen (H) isotopes of sedimentary plant waxes to reconstruct precipitation isotopes, which relate to moisture pathways and local climate conditions, and highlight where new tools like coupled oxygen (O) and H isotope records or new H isotope proxies show strong promise. In particular, I’ll focus on my work using H isotopes of leaf wax biomarkers to reconstruct precipitation isotopes at multiple sites on Greenland for the last 10,000 years, compare sedimentary wax H isotope data to the oxygen (O) isotopic composition of aquatic insects from the same records, and highlight recent discoveries regarding the strengths and weaknesses of wax biomarkers in this pursuit. Additionally, I’ll introduce ongoing work to relate the H isotopic composition of n-alkyl chains derived from brGDGTs to that of soil and lake water isotopes in Arctic Canada.
Sarah Shelley
Postdoc, Carnegie Museum
October 20, 2020
The Rise of Mammals after the End-Cretaceous Mass Extinction
Living mammals exhibit vast morphological and ecological diversity from the tiny two-gram bumblebee bat capable of powered flight to the fully aquatic deep-diving blue whale, the largest animal known to have ever existed. The foundations of mammal diversity were established in the Mesozoic, but it was not until after the end-Cretaceous mass extinction and the demise of the non-avian dinosaurs that mammals began to increase in body size, diversify into many new species and establish the extant lineages we recognise today. Despite a global presence, fundamental questions regarding the evolutionary relationships and divergence dates of placental mammals remain largely unresolved. This is thought to be, in part, due to our relatively poor knowledge regarding the palaeobiology and phylogeny of the Paleocene mammals, those species that diversified immediately after the extinction, and which are often perceived as ‘archaic’ precursors to the extant lineages.
This talk focuses on some of the broader goals of my on-going research into Paleocene mammal palaeobiology and phylogeny and will discuss the findings of a recent project investigating the locomotor ecology of Paleocene mammals. Results from this study show that Paleocene mammals were far from ‘archaic’ precursors, instead they were products of a post-extinction adaptive radiation that combined a basic placental mammal bauplan with inimitable anatomical specialisations not easily comparable to extant mammals, exemplifying their evolution following a catastrophic mass extinction event.
Aviwe Matiwane
PhD, Rhodes University
October 13, 2020
A New Approach to Glossopteris Leaf Taxonomy Embracing Morphometric Analyses
Glossopteris leaves are one of the most common and easily recognised Permian fossils across Gondwana, but they are morphologically conservative and taxonomic approaches to species differentiation have been varied, relying on visual estimations of relatively plastic characteristics such as shape, length etc. Species identification in the past has therefore proven to be subjective, inconsistent and extremely challenging.
To address these taxonomic challenges, we have produced the first morphometric study using Glossopteris leaves from two localities in the Karoo Basin of South Africa: a new site on the Ouberg Pass (Northern Cape Province) and Kwa-Yaya (KwaZulu-Natal Province). The Ouberg Pass lies in the southern Karoo Basin, in a region rich in fossils of terrestrial vertebrates of the Tapinocephalus Assemblage Zone. A detailed biostratigraphic framework, together with multiple ash dates in the immediate area, provided excellent context for this study of a well-preserved, middle Permian parautochthonous flora. The Kwa-Yaya locality, in the late Permian Emakwezini Formation of the Lebombo Basin in the eastern Karoo Basin, has yielded a superbly preserved and diverse, parautochthonous flora. For this study, 43 qualitative leaf features were measured and analysed to identify morphological characteristics that could produce well defined specimen clusters. The morphometric analysis included: leaf length, width, vein angles (proximal, medial, and marginal), mesh areas and width, and leaf area among other features. Fifteen qualitative features were also considered. Our results suggest that the use of the medial portion of the leaf produced the most discrete clusters; and that a combination of features (vein angles, mesh width, mesh area, and leaf area) provided the most reasonable grounds for morphologically defined taxonomic discrimination of species. This work has been used for the development of a standardized leaf characterization template that we hope will facilitate more reliable and consistent typification of glossopterid leaves in South Africa and other regions of Gondwana.
Allison Karp
Postdoc, Yale University
October 6, 2020
Burning Questions: The role of fire ecology in the Neogene expansion of C4 grasslands
Fire is crucial to maintaining modern subtropical grasslands, yet our empirical support for the origins and evolution of this association is limited by a dearth of coeval records of both grass and fire proxies in pre-Quaternary sediments. Polycyclic aromatic hydrocarbons (PAHs) are a suite of molecules that can derive both from the burning of terrestrial vegetation and from thermal maturation of organic matter. I developed an approach to quantitatively source these molecules to enable reconstructions of Neogene fire occurrence. Here, I test hypothesis that fire-feedbacks facilitated the rise of C4 vegetation in the Mio-Pliocene using Pyrogenic PAH abundance patterns alongside records of δ13C of leaf waxes on two continents. Fire-derived PAH relative abundances jumped an order of magnitude in association with a rise in grass inputs recorded at the landscape (Pakistan) and continental scale (Bengal Fan) in South Asia, but not in Australia. These results support fire disturbance as a critical mechanism of terrestrial biome transitions, but emphasize the need to reconstruct fire explicitly alongside other climate and ecological variables, as fire-feedbacks can differ drastically between continents.
Jorge Cardich
Asst. Professor, Universidad Peruana Cayetano Heredia
September 29, 2020
(Paleo)Ecology of benthic foraminifera in anoxic sediments: the reconstruction of the OMZ off Peru in the last millenium
Benthic foraminifera are testate protists that thrive in several extreme environments, such as sediments of oxygen minimum zones (OMZ). The natural variability of OMZs is shaped by climate and ocean dynamics, but anthropogenic forcing increases the oxygen deficiency near the coast. In Peru, the OMZ is shallow and intense and has suffered changes in the past. How is it responding in recent centuries? Is it expanding with global warming? Here I show how ‘forams’ reflect the changing environmental conditions of OMZ off Peru in the last millenium through their ecological features.
Gabi Serrato Marks
PhD, MIT-WHOI
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.
Aaron Martinez
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.
Matthew Jones
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.
Charuta Kulkarni
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.
Caitlyn Witkowski
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.
Deepak Jha
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.
Mairin Balisi
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.
Emma Dunne
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.
Pedro Monarrez
Postdoc, Stanford University
July 21, 2020
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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
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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.
Neil Brocklehurst
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.
Heather Jones
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.
Laura Haynes
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.
