Pedro M. Monarrez

Global diversity patterns delineate the Serpukhovian (Upper Mississippian, Carboniferous) mass extinction as the sixth-largest of the Phanerozoic, with 26–28% of genera extinct. Studies of Serpukhovian marine assemblages from North America, however, exhibit stable diversity patterns across the Serpukhovian–Bashkirian boundary. These studies provide evidence against an extinction event during the Serpukhovian, with observed taxonomic turnover attributable to extirpation and facies preservation rather than true extinction. Here, we provide further insight into the Serpukhovian extinction at the mid-Carboniferous Global Boundary Stratotype Section and Point in Arrow Canyon, southern Nevada, US. Assessing brachiopod assemblages within their facies context, we test for evidence of the Serpukhovian mass extinction. Results reveal that 39% of Serpukhovian genera are absent from the Bashkirian at Arrow Canyon. However, global stratigraphic ranges reveal that all but two Serpukhovian taxa persisted into the Bashkirian. Multivariate analysis reveals similar taxonomic composition between the Serpukhovian and Bashkirian assemblages, with a notable lithological gradient driving local variation between geologic units. These results further suggest the absence of a late Serpukhovian extinction event in North America and highlight how working with the structure of the stratigraphic record can separate biological signals from stratigraphic patterns.

Global warming is often predicted to drive universal declines in animal body size, but empirical evidence remains equivocal. This is particularly true in marine systems, where body size distributions are influenced not only by temperature but also by oxygen and productivity, all of which are expected to be greatly altered in future oceans. Differences in regional climate trajectories and the physiology of marine taxa also suggest that body size responses will not be spatially or ecologically uniform. We address these complexities by projecting future changes in mean body size across species within ocean basins using a database of 23,329 marine mollusc species. We quantify how body size distributions change across energetic gradients and forecast assemblage level shifts of the five major classes of molluscs across all 10 oceanic basins. Under high greenhouse gas emission scenarios, we project a significant decline in body size in 68% of class–basin combinations (34 of 50), with some clades expected to shrink by ~16% in mean length by 2100. However, these responses are not universal but are governed by clade-level differences in dominant ecological and physiological strategies and the geography of climate change. Because biomass scales allometrically with length, these trends can correspond to substantial changes in the mass of the average species, from a 46% decline to a 15% increase depending on clade and region. Such widespread functional disruptions may threaten critical ecosystem services (carbon sequestration, nutrient cycling, and human food provisioning), with implications for global marine ecosystem functioning and services.

Global diversity patterns delineate the Serpukhovian (Upper Mississippian, Carboniferous) mass extinction as the sixth-largest of the Phanerozoic, with 26–28% of genera extinct. Studies of Serpukhovian marine assemblages from North America, however, exhibit stable diversity patterns across the Serpukhovian–Bashkirian boundary. These studies provide evidence against an extinction event during the Serpukhovian, with observed taxonomic turnover attributable to extirpation and facies preservation rather than true extinction. Here, we provide further insight into the Serpukhovian extinction at the mid-Carboniferous Global Boundary Stratotype Section and Point (GSSP) in Arrow Canyon, southern Nevada, USA. Assessing brachiopod assemblages within their facies context, we test for evidence of the Serpukhovian mass extinction. Results reveal that 39% of Serpukhovian genera are absent from the Bashkirian at Arrow Canyon. However, global stratigraphic ranges reveal that all but two Serpukhovian taxa persisted into the Bashkirian. Multivariate analysis reveals similar taxonomic composition between the Serpukhovian and Bashkirian assemblages, with a notable lithological gradient driving local variation between geologic units. These results further suggest the absence of a late Serpukhovian extinction event in North America and highlight how working with the structure of the stratigraphic record can separate biological signals from stratigraphic patterns.

Fossil assemblages exhibit a global depletion in taxonomic distinctiveness in the aftermath of the end-Permian mass extinction (~252 million years ago), but little is known about why. Here, we examine whether biotic homogenization can be explained by tropical survivors tracking an expansion of their preferred habitat, measured in terms of the ratio of environmental oxygen supply to metabolic demand. We compare spatial similarity in community composition among marine invertebrate fossils represented by bivalve and gastropod fossils with predictions from an ecophysiological model of habitat that diagnoses areas in the ocean that can sustain the aerobic requirements of marine invertebrates. Modeled biogeographic responses to climate change yield an increase in global similarity of community composition among surviving ecophysiotypes, consistent with patterns in the fossil record and arguing for a physiological control on earliest Triassic biogeography.

Two of the traits most often observed to correlate with extinction risk in marine animals are geographical range and body size. However, the relative effects of these two traits on extinction risk have not been investigated systematically for either background times or during mass extinctions. To close this knowledge gap, we measure and compare extinction selectivity of geographical range and body size of genera within five classes of benthic marine animals across the Phanerozoic using capture–mark–recapture models. During background intervals, narrow geographical range is strongly associated with greater extinction probability, whereas smaller body size is more weakly associated with greater extinction probability. During mass extinctions, the association between geographical range and extinction probability is reduced in every class and fully eliminated in some, whereas the association between body size and extinction probability varies in strength and direction across classes. While geographical range is universally the stronger predictor of survival during background intervals, variation among classes during mass extinction suggests a fundamental shift in extinction processes during these global catastrophes.

Ancient hyperthermal events in Earth’s history are ideal to isolate the evolutionary consequences of climate change and other environmental factors from other anthropogenic influences. A key biological trait hypothesized to be sensitive to climate change and straightforward to quantify in fossil data is body size. Most ectotherms modulate their physiological response to temperature and oxygen change in part through their body size. As hyperthermal events include both temperature increases and ocean deoxygenation, these events can have a deleterious effect on ectotherms on the ends of the body size spectrum. Large bodied ectotherms are particularly at risk, as oxygen demand increases with both body size and temperature. Previous work has assessed extinction selectivity of body size across hyperthermal events, but origination selectivity has not been assessed, which may be as important as extinction selectivity. Here, we measure extinction and origination selectivity with respect to body size for genera in six Linnean classes with robust fossil records (Rhynchonellata, Cephalopoda, Echinoidea, “bony fish” [an informal class consisting of Osteichthyes, Actinopteri, and Actinopterygii], Bivalvia, and Gastropoda). We compare selectivity during background intervals with those during hyperthermal events and their associated recovery intervals spanning the Middle Triassic to the Recent. We use capture-mark-recapture statistical models to measure extinction and origination selectivity while addressing the effects of variable sampling completeness with respect to time and body size. We find that genera with smaller body size are preferentially lost to extinction during background intervals, whereas body size is not associated with extinction probability during hyperthermal events. Conversely, originating genera are larger than average during background intervals across all size classes, but vary among classes in their body size pattern immediately following hyperthermal events. Rhynchonellate brachiopods, cephalopods, and echinoids exhibit originators that are smaller, on average, than the survivors after hyperthermal events, whereas originating bivalves and gastropods tend to be larger than the survivors. Bony fish do not exhibit size bias in origination after hyperthermal events. Overall, these results show that hyperthermal events affect both extinction and origination dynamics but have a greater effect on body size origination selectivity than extinction. The exact cause(s) for the greater effect of hyperthermal events on body size in origination versus extinction is not certain, but these results are consistent with previous findings spanning the Phanerozoic that compared body size selectivity patterns during background intervals to those associated with the Big Five mass extinction events. These results show that climate-associated perturbations change extinction and origination dynamics relative to background intervals, suggesting that climate-associated extinction and origination in the modern and future ocean may differ from geological background.

A central question in the study of mass extinction is whether these events simply intensify background extinction processes and patterns versus change the driving mechanisms and associated patterns of selectivity. Over the past two decades, aided by the development of new fossil occurrence databases, selectivity patterns associated with mass extinction have become increasingly well quantified and their differences from background patterns established. In general, differences in geographic range matter less during mass extinction than during background intervals, while differences in respiratory and circulatory anatomy that may correlate with tolerance to rapid change in oxygen availability, temperature, and pH show greater evidence of selectivity during mass extinction. The recent expansion of physiological experiments on living representatives of diverse clades and the development of simple, quantitative theories linking temperature and oxygen availability to the extent of viable habitat in the oceans have enabled the use of Earth system models to link geochemical proxy constraints on environmental change with quantitative predictions of the amount and biogeography of habitat loss. Early indications are that the interaction between physiological traits and environmental change can explain substantial proportions of observed extinction selectivity for at least some mass extinction events. A remaining challenge is quantifying the effects of primary extinction resulting from the limits of physiological tolerance versus secondary extinction resulting from the loss of taxa on which a given species depended ecologically. The calibration of physiology-based models to past extinction events will enhance their value in prediction and mitigation efforts related to the current biodiversity crisis.

We highlight the historical and contemporary policies that govern paleontological research on federally recognized Native American lands. The United States has a long history of fossil dispossession from Indigenous Peoples, and federal policies surrounding the management of Native American lands (i.e., reservations), and the geological resources therein, have changed through time. These changes reflect shifting popular and political ideologies regarding Native American nations’ sovereignty and self-governance. As of 2022, the United States has a government-to-government relationship with federally recognized Tribal entities, but that has not always been the case. Historians have divided post-contact Native American federal policy into distinct eras: Colonial Times to 1820, Native American Removal and Reservation (1820–1887), Allotments and Attempted Assimilation (1887–1934), Reorganization and Preservation (1934–1953), Termination and Relocation (1953–1968), and Tribal Self-Determination (1968–present). Documentation of how the federal policies from each of these eras continue to impact current paleontological research is limited. We summarize major legislative actions, court cases, and historical events that have affected paleontological resource management in Native American territory. We use this historical context to identify federal policy gaps and highlight legal nuances associated with fossil collection and ownership, particularly given the importance of fossils to some Native Americans’ cultural patrimony. Finally, we explore how these gaps affect scientific research and highlight best practices for conducting paleontological research on vertebrate, invertebrate, and paleobotanical body and trace fossils using the CARE (Collective Benefit, Authority to Control, Responsibility, Ethics) Principles for Indigenous Data Governance ( https://www.gida-global.org/care ).

The end-Permian mass extinction event resulted in the loss of approximately 80% to 90% of marine animal species due to drastic changes in climate. Because warming was a major factor in the extinction, it has been theorized the organisms that did survive were able to do so because they moved to higher latitudes and this hypothesis is consistent with tetrapod data. We hypothesized that this relationship holds true for marine mollusks and arthropods as well. Using Changhsingian (Late Permian) and Induan (Early Triassic) data from the Paleobiology Database, we extracted occurrences of classes Bivalvia, Cephalopoda, Gastropoda, and Ostracoda, which had 2433, 395, 379, and 1717 genus occurrences, respectively. Then, we used the paleolatitude data for each genus occurrence to characterize the latitude distribution of each class before and after the Permian/Triassic transition. We compared the paleolatitude medians before and after the mass extinction for each class to quantify the latitude shift for each class: 23.18° for Bivalvia, 37.45° for Cephalopoda, 29.82° for Gastropoda, and 6.29° for Ostracoda. This finding indicates that each individual class had a different latitudinal shift, with all classes exhibiting a poleward shift north. We also conducted Welch t-tests to compare the differences in latitudinal ranges and found that they were significant (Bivalvia: p < 2.2e-16, Cephalopoda: p = 3.83e-6, Gastropoda: p < 2.2e-16, Ostracoda: p = 0.0030). In addition, we ran multiple randomized models to compare them with our original results and found a significant difference between them via the Kolmogorov-Smirnov test, which means that the northward migration could be a biological response. Moreover, the results of our study show that the overall latitudinal range of most classes contracted after the extinction event, with the exception of the Cephalopoda class.

Extinction within the Paleozoic era has been studied in the past, but there still lacks a comprehensive understanding of how extinction risk changed throughout it. Our research project aims to bridge this gap by exploring extinction risk in relation to major Paleozoic phyla and ecological characteristics. Using R, we analyzed the Stanford Earth Body Size dataset, which includes extensive data (n=8816) on Paleozoic marine animals. In Step 1, regression coefficients were formed, indicating whether being in one of the 6 phyla in each period of the Paleozoic era conferred greater or less extinction risk. In Step 2, the examined ecological characteristics included ocean acidification resilience, feeding patterns, body volume, length, surface area, motility, tiering, circulatory systems, and respiratory organ type. In Step 3, 6 binomial machine learning models were created using the traits from Step 2 to determine whether an individual genus went extinct in a particular period. Our Step 1 results confirm that within these timeframes, while certain phyla have greater extinction risk, extinction risk was not uniform across these groups. Our Step 2 results show certain traits provided advantages and disadvantages for an organism’s extinction risk. One interesting pattern was that the only consistently non-significant traits were body length, area, and volume. Likewise with Step 1, extinction risk for each ecological characteristic varied across the Paleozoic. Finally, in Step 3, the results were largely successful. Most of the six models had an accuracy above 80% with the highest being 92% in the Cambrian. The areas under the Precision-Recall and the Receiver Operating Characteristic Curves were all in the acceptable (<0.6) range, demonstrating that the model has low false positive/ negative rates and is able to distinguish between what trait indicates extinction or survival for each period. Our research project identified phyla at risk of extinction in each period of the Paleozoic, determined which natural traits incited greater extinction risk, and demonstrated machine learning models trained on fossil descriptors can predict when an individual genus became extinct. Our results confirmed that extinction risk is not consistently dependent on a singular factor nor is it constant across every period of the Paleozoic era.