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.
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.