Showing papers in "Paleobiology in 2023"

Linking host plants to damage types in the fossil record of insect herbivory

Abstract: Abstract Studies of insect herbivory on fossilized leaves tend to focus on a few, relatively simple metrics that are agnostic to the distribution of insect damage types among host plants. More complex metrics that link particular damage types to particular host plants have the potential to address additional ecological questions, but such metrics can be biased by sampling incompleteness due to the difficulty of distinguishing the true absence of a particular interaction from the failure to detect it—a challenge that has been raised in the ecological literature. We evaluate a range of methods for characterizing the relationships between damage types and host plants by performing resampling and subsampling exercises on a variety of datasets. We found that the components of beta diversity provide a more valid, reliable, and interpretable method for comparing component communities than do bipartite network metrics and that the rarefaction of interactions represent a valid, reliable, and interpretable method for comparing compound communities. Both beta diversity and rarefaction of interactions avoid the potential pitfalls of multiple comparisons. Finally, we found that the host specificity of individual damage types is challenging to assess. Whereas bipartite network metrics are sufficiently biased by sampling incompleteness to be inappropriate for fossil herbivory data, alternatives exist that are perfectly suitable for fossil datasets with sufficient sample coverage.

Hydrodynamic trade-offs in potential swimming efficiency of planispiral ammonoids

Abstract: Abstract. Ammonoid cephalopods were Earth's most abundant oceanic carnivores for hundreds of millions of years, yet their probable range of swimming capabilities is poorly constrained. We investigate potential hydrodynamic costs and advantages provided by different conch geometries using computational fluid dynamics simulations. Simulations of raw drag demonstrate expected increases with velocity and conch inflation, consistent with published experimental data. Analysis at different scales of water turbulence (via Reynolds number) reveals dynamic trade-offs between conch shape, size, and velocity. Among compressed shells, the cost of umbilical exposure makes little difference at small sizes (and/or low velocity) but is profound at large sizes (and/or high velocity). We estimate that small ammonoids could travel one to three diameters per second (i.e., a typical ammonoid with a 5-cm-diameter shell could travel 5–15 cm/s), but that large ammonoids faced greater discrepancies (a 10 cm serpenticone likely traveled <30 cm/s, while a 10 cm oxycone might achieve >40 cm/s). All of these velocities are proposed only for short bursts of jet propulsion, lasting only a few seconds, in the service of dodging a predator or conspecific rival. These analyses do not include phylogeny, taxonomy, second-order conch architecture (ribs, ornament, etc.), or hydrostatic consequences of internal anatomy (soft body, suture complexity). For specific paleoecological context, we consider how these results inform our reconstruction of Jurassic ammonite recovery from the end-Triassic mass extinction. Greater refinements will come with additional simulations that measure how added mass is influenced by individual shape-trait variations, ornament, and subtle body extensions during a single jet motion.

Challenges and directions in analytical paleobiology

Abstract: Over the last 50 years, access to new data and analytical tools has expanded the study of analytical paleobiology, contributing to innovative analyses of biodiversity dynamics over Earth's history. Despite—or even spurred by—this growing availability of resources, analytical paleobiology faces deep-rooted obstacles that stem from the need for more equitable access to data and best practices to guide analyses of the fossil record. Recent progress has been accelerated by a collective push toward more collaborative, interdisciplinary, and open science, especially by early-career researchers. Here, we survey four challenges facing analytical paleobiology from an early-career perspective: (1) accounting for biases when interpreting the fossil record; (2) integrating fossil and modern biodiversity data; (3) building data science skills; and (4) increasing data accessibility and equity. We discuss recent efforts to address each challenge, highlight persisting barriers, and identify tools that have advanced analytical work. Given the inherent linkages between these challenges, we encourage discourse across disciplines to find common solutions. We also affirm the need for systemic changes that reevaluate how we conduct and share paleobiological research.

A downcore increase in time averaging is the null expectation from the transit of death assemblages through a mixed layer

Abstract: Abstract Understanding how time averaging changes during burial is essential for using Holocene and Anthropocene cores to analyze ecosystem change, given the many ways in which time averaging affects biodiversity measures. Here, we use transition-rate matrices to explore how the extent of time averaging changes downcore as shells transit through a taphonomically complex mixed layer into permanently buried historical layers: this is a null model, without any temporal changes in rates of sedimentation or bioturbation, to contrast with downcore patterns that might be produced by human activity. Assuming stochastic burial and exhumation movements of shells between increments within the mixed layer and stochastic disintegration within increments, we find that almost all combinations of net sedimentation, mixing, and disintegration produce a downcore increase in time averaging (interquartile range [IQR] of shell ages), this trend is typically associated with a decrease in kurtosis and skewness and by a shift from right-skewed to symmetrical age distributions. A downcore increase in time averaging is thus the null expectation wherever bioturbation generates an internally structured mixed layer (i.e., a surface, well-mixed layer is underlain by an incompletely mixed layer): under these conditions, shells are mixed throughout the entire mixed layer at a slower rate than they are buried below it by sedimentation. This downcore trend created by mixing is further amplified by the downcore decline in disintegration rate. We find that transition-rate matrices accurately reproduce the downcore changes in IQR, skewness, and kurtosis observed in bivalve assemblages from the southern California shelf. The right-skewed shell age-frequency distributions typical of surface death assemblages—the focus of most actualistic research—might be fossilized under exceptional conditions of episodic anoxia or sudden burial. However, such right-skewed assemblages will typically not survive transit through the surface mixed layer into subsurface historical layers: they are geologically transient. The deep-time fossil record will be dominated instead by the more time-averaged assemblages with weakly skewed age distributions that form in the lower parts of the mixed layer.

Fitting and evaluating univariate and multivariate models of within-lineage evolution

Abstract: The nature of phenotypic evolution within lineages is central to many unresolved questions in paleontology and evolutionary biology. Analyses of evolutionary time series of ancestor–descendant populations in the fossil record are likely to make important contributions to many of these debates. However, the limited number of models that have been applied to these types of data may restrict our ability to interpret phenotypic evolution in the fossil record. Using uni- and multivariate models of trait evolution that make different assumptions regarding the dynamics of the adaptive landscape, I evaluate contrasting hypotheses to explain evolution of size in the radiolarian Eucyrtidium calvertense and armor in the stickleback Gasterosteus doryssus. Body-size evolution in E. calvertense is best explained by a model in which the lineage evolves as a consequence of a shift in the adaptive landscape that coincides with the initiation of neosympatry with its sister lineage. Multivariate evolution of armor traits in a stickleback lineage (G. doryssus) shows evidence of adaptation toward independent optima on the adaptive landscape at the same time as traits change in a correlated fashion. The fitted models are available in the R package evoTS, which builds on the paleoTS framework.

Spatial heterogeneity in benthic foraminiferal assemblages tracks regional impacts of paleoenvironmental change across Cretaceous OAE2

Abstract: The impact of global climate events on local ecosystems can vary spatially. Understanding this potential heterogeneity can illuminate which environments will be most impacted and the proximal drivers of ecosystem responses. Cenomanian–Turonian marine deposits of the Western Interior Seaway (WIS) record paleoceanographic changes associated with the Greenhorn transgression and the onset of Oceanic Anoxic Event 2 (OAE2). They provide an ideal setting to study basin-wide paleoecological responses during a global perturbation. Here, we integrate benthic foraminiferal assemblages from before, during, and after OAE2 via multivariate ordination analysis to examine spatial patterns in faunal responses across the western United States on a common scale and to interrogate a previously defined faunal marker commonly used for basin-wide correlation, the Benthonic Zone (BZ). We identify oxygenation and organic matter quality as primary and secondary controls of faunal variation across the 10 stratigraphic records and use this variation to infer paleoenvironmental changes. Stratigraphic trends reveal, in contrast to previous studies, deoxygenation at the onset of OAE2. They also reveal temporal patterns in oxygenation and productivity consistent with the gradual northward migration of a southern water mass into the WIS. This spatial heterogeneity hinders the use of the BZ as a temporal marker, because assemblages change in response to diachronous environmental change, and thus timing of the BZ with respect to OAE2 is not consistent across the basin. Our study demonstrates that regional processes can overshadow ecosystem responses to global events and underscores the importance of considering how changes in the position of water masses impact the expression of global biogeochemical perturbations.

Is the hyoid a constraint on innovation? A study in convergence driving feeding in fish-shaped marine tetrapods

Abstract: The hyoid apparatus is essential for underwater feeding in marine tetrapods, but it is unclear whether this complex has evolved as convergently as other traits, such as dentition or locomotion. Here we compare the ossified hyoid elements in ophthalmosaurid ichthyosaurs and odontocete cetaceans, two groups with an overall similar body shape, to understand whether the hyoid elements show any signs of convergence in the context of feeding. We examined three types of data (size, morphology, and internal bone microstructure) in ophthalmosaurid and odontocete taxa in which these elements are preserved. Our data show that ichthyosaurs never experienced a shift in feeding mode, which might indicate that their hyoid apparatus never adapted to suction feeding. Also, the internal microstructure of the two animal groups differs; where the odontocetes have an overall less compact structure, ophthalmosaurid ichthyosaurs have cancellous inner cones in an outer, more compact sheath. These differences are likely explained as biomechanical adaptations to different feeding modes. Thus, the hyoid changed less and acted more as a constraint for feeding innovation in ichthyosaurs compared with cetaceans, and through a much longer time span (more than 150 Myr).

Linking host plants to damage types in the fossil record of insect herbivory – CORRIGENDUM

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Relative oversampling of carbonate rocks in the North American marine fossil record

Abstract: Paleontologists have long stressed the need to know how sampling the fossil record might influence our knowledge of the evolution of life. Here, we combine fossil occurrences of North American marine invertebrates from the Paleobiology Database with lithologic data from Macrostrat to identify sampling patterns in carbonate and siliciclastic rocks. We aim to quantify temporal trends in sampling effort within and between lithologies, focusing on the proportion of total available volume that has been sampled (sampled fossiliferous proportion, here called κ). Results indicate that the sampled fossiliferous proportion was stable during the Paleozoic, and variable during the post-Paleozoic, but showed no systematic increase through time. Fossiliferous carbonate rocks are proportionally more sampled than siliciclastic rocks, with intervals where the carbonate κ is double the siliciclastic κ. Among possible explanations for the apparent oversampling of fossiliferous carbonate rocks, analyses suggest that barren units, taphonomic dissolution, or data entry errors cannot completely explain sampling patterns. Our results suggest that one of the important drivers might be that paleontologists publish taxonomic descriptions from carbonate rocks more frequently. The higher diversity in carbonate rocks might account for an ease in the description of unknown species and therefore a higher rate of published fossils. Finally, a strong effect in favor of carbonate rocks might distort our perception of diversity through time, even under commonly used standardization methods. Our results also confirm that previous descriptions of an increase in the proportion of sampled fossiliferous rocks over time were driven by the sampling of the nonmarine fossil record.

A paleothermometer for the northern Andes based on C3–C4 grass phytoliths

Abstract: Grass-dominated ecosystems cover ~40% of Earth's terrestrial surface, with tropical grasses accounting for ~20% of global net primary productivity. C3 (cool/temperate) and C4 (tropical and subtropical) grass distribution is driven primarily by temperature. In this work, we used phytolith assemblages collected from vegetation plots along an elevation and temperature gradient in the northern Andes (Colombia and Ecuador) to develop a paleothermometer for the region. To accomplish this, we created a transfer function based on the inverse relationship between mean annual temperature (MAT) and the phytolith-based climatic index (Ic), which is the proportion of C3 over C4 grass phytoliths (GSSCP). To evaluate how accurately the index reflects C4–C3 grass abundance in vegetation plots, we compared it with semiquantitative floristic estimates of C4–C3 grass abundance. To further evaluate the 1 − Ic index as a proxy for C4–C3 grass abundance, we compared it with corresponding δ13C values (an independent proxy for C4–C3 vegetation). Results indicate that (1) GSSCP assemblages correctly estimate C4–C3 grass abundance in vegetation plots; (2) the Ic index outperforms the δ13C record in estimating C4–C3 grass abundance, even in open-vegetation types; and (3) our Ic index–based model accurately predicts MAT. This new calibrated proxy will help improve paleotemperature reconstructions in the northern Andes since at least the emergence and spread of C4 grasses in the region during the late Miocene.

Estimating spatial variation in origination and extinction in deep time: a case study using the Permian–Triassic marine invertebrate fossil record

Abstract: Understanding spatial variation in origination and extinction can help to unravel the mechanisms underlying macroevolutionary patterns. Although methods have been developed for estimating global origination and extinction rates from the fossil record, no framework exists for applying these methods to restricted spatial regions. Here, we test the efficacy of three metrics for regional analysis, using simulated fossil occurrences. These metrics are then applied to the marine invertebrate record of the Permian and Triassic to examine variation in extinction and origination rates across latitudes. Extinction and origination rates were generally uniform across latitudes for these time intervals, including during the Capitanian and Permian–Triassic mass extinctions. The small magnitude of this variation, combined with the possibility of its attribution to sampling bias, cautions against linking any observed differences to contrasting evolutionary dynamics. Our results indicate that origination and extinction levels were more variable across clades than across latitudes.

Bedrock geological map predictions for Phanerozoic fossil occurrences

Abstract: Geographically explicit, taxonomically resolved fossil occurrences are necessary for reconstructing macroevolutionary patterns and for testing a wide range of hypotheses in the Earth and life sciences. Heterogeneity in the spatial and temporal distribution of fossil occurrences in the Paleobiology Database (PBDB) is attributable to several different factors, including turnover among biological communities, socioeconomic disparities in the intensity of paleontological research, and geological controls on the distribution and fossil yield of sedimentary deposits. Here we use the intersection of global geological map data from Macrostrat and fossil collections in the PBDB to assess the extent to which the potentially fossil-bearing, surface-expressed sedimentary record has yielded fossil occurrences. We find a significant and moderately strong positive correlation between geological map area and the number of fossil occurrences. This correlation is consistent regardless of map unit age and binning protocol, except at period level; the Neogene and Quaternary have non-marine map units covering large areas and yielding fewer occurrences than expected. The sedimentary record of North America and Europe yields significantly more fossil occurrences per sedimentary area than similarly aged deposits in most of the rest of the world. However, geographic differences in area and age of sedimentary deposits lead to regionally different expectations for fossil occurrences. Using the sampling of surface-expressed sedimentary units in North America and Europe as a predictor for what might be recoverable from the surface-expressed sedimentary deposits of other regions, we find that the rest of the globe is approximately 45% as well sampled in the PBDB. Using age and area of bedrock and sampling in North America and Europe as a basis for prediction, we estimate that more than 639,000 occurrences from outside these regions would need to be added to the PBDB to achieve global geological parity in sampling. In general, new terrestrial fossil occurrences are expected to have the greatest impact on our understanding of macroevolutionary patterns.

Is the hyoid a constraint on innovation? A study in convergence driving feeding in fish-shaped marine tetrapods – CORRIGENDUM

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Anomalous 13C enrichment in Mesozoic vertebrate enamel reflects environmental conditions in a “vanished world” and not a unique dietary physiology

Abstract: Biogeochemical analyses of organisms’ tissues provide direct proxies for diets, behaviors, and environmental interactions that have proven invaluable for studies of extant and extinct species. Applying these to Cretaceous ecosystems has at times produced anomalous results, however, as dinosaurs preserve unusually positive stable carbon isotope compositions relative to extant C3-feeding vertebrates. This has been hypothesized to be a unique property of dinosaur dietary physiology, with potential significance for our interpretations of their paleobiology. We test that hypothesis through multi-taxic stable carbon isotope analyses of a spatiotemporally constrained locality in the Late Cretaceous of Canada, and compare the results to a modern near-analogue environment in Louisiana. The stable carbon isotope anomaly is present in all sampled fossil vertebrates, dinosaur or not. This suggests another more widespread factor is responsible. Examinations of diagenetic effects suggest that, where present, they are insufficient to explain the isotope anomaly. The isotope anomaly is therefore not primarily the result of a unique dietary physiology of dinosaurs, but rather a mix of factors impacting all taxa, such as environmental and/or source-diet differences. Our study underscores the importance of multi-taxic samples from spatiotemporally constrained localities in testing hypotheses of extinct organisms and ecosystems, and in the use of modern data to “ground truth” when evaluating analogue versus non-analogue conditions in greenhouse paleoecosystems.

Convergent evolution of spherical shells in Miocene planktonic foraminifera documents the parallel emergence of a complex character in response to environmental forcing

Abstract: The spherical encompassing final chamber of the planktonic foraminifera Orbulina universa is a prime example of a complex character whose evolution has been documented by a sequence of intermediate forms. However, the mechanism that induced evolution of the spherical chamber remain unclear. Here we show that shortly after the emergence of Orbulina, documented throughout the oceans, a convergent evolutionary transition occurred in the semi-isolated Paratethys, leading to the emergence of the endemic Velapertina, which occupied a similar niche to Orbulina in the surface waters. Using X-ray computed tomography scanning, we show that the evolution of the encompassing final chamber involved the same sequence of steps in both lineages, combining a progressively spherical shell shape with changes in the position, number, and sizes of apertures. The similarity in the sequence of character acquisitions suggests structural determinism in the way foraminiferal shells are constructed and the presence of natural selection favoring a spherical morphology. Collectively, the emergence of spherical chambers in the two lineages at a similar time suggests that the evolution of this spectacular complex character occurred in response to a singular environmental driver.

Frond orientations with independent current indicators demonstrate the reclining rheotropic mode of life of several Ediacaran rangeomorph taxa

Abstract: Fossils from the deep-sea Ediacaran biotas of Newfoundland are among the oldest architecturally complex soft-bodied macroorganisms on Earth. Most organisms in the Mistaken Point–type biotas of Avalonia—particularly the fractal-branching frondose Rangeomorpha— have been traditionally interpreted as living erect within the water column during life. However, due to the scarcity of documented physical sedimentological proxies associated with fossiliferous beds, Ediacaran paleocurrents have been inferred in some instances from the preferential orientation of fronds. This calls into question the relationship between frond orientation and paleocurrents. In this study, we present an integrated approach from a newly described fossiliferous surface (the “Melrose Surface” in the Fermeuse Formation at Melrose, on the southern portion of the Catalina Dome in the Discovery UNESCO Global Geopark) combining: (1) physical sedimentological evidence for paleocurrent direction in the form of climbing ripple cross-lamination and (2) a series of statistical analyses based on modified polythetic and monothetic clustering techniques reflecting the circular nature of the recorded orientation of Fractofusus misrai specimens. This study demonstrates the reclining rheotropic mode of life of the Ediacaran rangeomorph taxon Fractofusus misrai and presents preliminary inferences suggesting a similar mode of life for Bradgatia sp. and Pectinifrons abyssalis based on qualitative evidence. These results advocate for the consideration of an alternative conceptual hypothesis for position of life of Ediacaran organisms in which they are interpreted as having lived reclined on the seafloor, in the position that they are preserved.

PAB volume 49 issue 2 Cover and Front matter

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Drilling predation on Early Jurassic bivalves and behavioral patterns of the presumed gastropod predator—evidence from Pliensbachian soft-bottom deposits of northern Germany

Abstract: Abstract Drilling predation is a common reason for mortality of benthic mollusks but did not become common until the late Mesozoic. The scarcity of drill holes in the early Mesozoic fossil record limits our understanding of the evolution of drilling behavior and its role on shaping early Mesozoic marine communities. Here, we use drilling traces on several bivalve taxa from the Lower Jurassic (Pliensbachian) marine soft-bottom deposits in northern Germany to explore behavioral patterns of the predator (e.g., site selectivity, change in site-selective behavior with age). Although none of the known drilling gastropod groups existed in the Pliensbachian, including the studied localities, the drill-hole morphology suggests that the predator was probably a gastropod. The ecology and identity of the target prey changes from a diverse array of epifaunal to infaunal taxa in older deposits to focus on a single, large, deep infaunal taxon, Gresslya intermedia , in younger deposits, suggesting a potential trend in prey selectivity over time. Spatial point pattern analysis of traces (SPPAT) reveals an aggregated pattern of drill holes on Gresslya , suggesting strong selectivity in drill-hole location. Drilling on a single large infaunal taxon and site selectivity are common patterns also inferred previously from the drilled deep infaunal Eothyasira from the Pliensbachian of southern Germany. In addition to the scarcity of predators, the highly specialized behavior of the early drilling predators, including strong prey selectivity in terms of prey identity and life habit, can partly explain the rarity of the early Mesozoic drill holes.

Diversification trajectories and paleobiogeography of Neogene chondrichthyans from Europe

Abstract: Abstract. Despite the rich fossil record of Neogene chondrichthyans (chimaeras, sharks, rays, and skates) from Europe, little is known about the macroevolutionary processes that generated their current diversity and geographical distribution. We compiled 4368 Neogene occurrences comprising 102 genera, 41 families, and 12 orders from four European regions (Atlantic, Mediterranean, North Sea, and Paratethys) and evaluated their diversification trajectories and paleobiogeographic patterns. In all regions analyzed, we found that generic richness increased during the early Miocene, then decreased sharply during the middle Miocene in the Paratethys, and moderately during the late Miocene and Pliocene in the Mediterranean and North Seas. Origination rates display the most significant pulses in the early Miocene in all regions. Extinction rate pulses varied across regions, with the Paratethys displaying the most significant pulses during the late Miocene and the Mediterranean and North Seas during the late Miocene and early Pliocene. Overall, up to 27% and 56% of the European Neogene genera are now globally and regionally extinct, respectively. The observed pulses of origination and extinction in the different regions coincide with warming and cooling events that occurred during the Neogene globally and regionally. Our study reveals complex diversity dynamics of Neogene chondrichthyans from Europe and their distinct biogeographic composition despite the multiple marine passages that connected the different marine regions during this time.

Ankylosaurian body armor function and evolution with insights from osteohistology and morphometrics of new specimens from the Late Cretaceous of Antarctica

Abstract: The body armor of ankylosaurians is a unique morphological feature among dinosaurs. While ankylosaurian body armor has been studied for decades, paleohistological analyses have only started to uncover the details of its function. Yet there has been an overall bias toward sampling ankylosaurian remains from the Northern Hemisphere, with limited quantitative studies on the morphological and functional evolution of the osteoderms composing their body armor. Here, we describe new ankylosaurian materials recovered from the Late Cretaceous of Antarctica that, in combination with data compiled from the literature, reveal new insights into the evolution of the ankylosaurian body armor. Based on histological microstructure and phylogenetic results, the new Antarctic material can be assigned to Nodosauridae. This group shares the absence/poor development of their osteodermal basal cortex and highly ordered sets of orthogonal structural fibers in the superficial cortex. Our morphospace analyses indicate that large morphological diversity is observed among both nodosaurids and ankylosaurids, but osteoderms became more functionally specialized in late-diverging nodosaurids. Besides acting as effective protection against predation, osteoderms also exhibit highly ordered structural fibers in nodosaurids, enabling a decrease in cortical bone thickness (as in titanosaurs), which could have been co-opted for secondary functions, such as calcium remobilization for physiological balance. The latter may have played a key role in nodosaurid colonization of high-latitude environments, such as Antarctica and the Arctic Circle.

Patterns and processes in the history of body size in turritelline gastropods, Jurassic to Recent

Abstract: Abstract Body size is an important trait with implications for energy use and ecology as well as generation time and evolutionary rates. Turritelline gastropods are widely distributed through geologic time and space, making them an excellent group for evaluating macroevolutionary patterns. To evaluate the pattern of body-size change in turritelline gastropods, we compiled a dataset of shell lengths of 316 species of turritelline gastropods spanning the Jurassic to Recent. Type specimens were almost always significantly larger than specimen distributions from the same species. We found that turritelline gastropod size was inversely correlated with latitude, a trend likely driven by the Neogene–Recent diversification of small-bodied Southern Hemisphere taxa. A time series model was applied to distinguish among three possible macroevolutionary patterns: unbiased random walk (no directional trend), biased random walk (directional trend), and stasis (no net change). We determined that turritelline gastropods have experienced stasis in body size throughout their evolutionary history, adding to the growing literature documenting directionless body-size trends in marine invertebrate clades. Stasis of geographically widespread clades may be the result of ecological variability across the environmental range occupied by the group or differential diversification into opposing environments. Turritelline life-history patterns, especially their reproductive strategy that combines a short life span and decline in growth rate around 1 year of age to reallocate energy to reproduction, might circumvent selection for longevity and larger size, while further decrease in minimum size is likely limited by feeding efficiency and anti-predatory defense. The expectation that species or clades should continue to evolve to occupy larger size classes conflicts with the evolutionary advantages of small size, which in turritelline gastropods include high generational turnover and larger population sizes that yield opportunities for genetic variance.

Growth allometry and dental topography in Upper Triassic conodonts support trophic differentiation and molar-like element function

Abstract: Abstract Conodont elements have high rates of morphological evolution, but the drivers of this disparity are debated. Positive allometric relationships between dimensions of food-processing surfaces and entire P 1 elements have been used to argue that these elements performed mechanical digestion. If involved in food processing, the surface of the element should grow at a rate proportional to the increase in energy requirements of the animal. This inference of function relies on the assumption that the energy requirements of the animal grew faster (≅ mass 0.75 ) than the tooth area (≅ mass 0.67 ). We reevaluate this assumption based on metabolic rates across animals and calculate the allometry in platform-bearing P 1 elements of Late Triassic co-occurring taxa, Metapolygnathus communisti and Epigondolella rigoi , using 3D models of ontogenetic series. Positive allometry is found in platform and element dimensions in both species, supporting a grasping-tooth hypothesis, based on the assumption that metabolic rate in conodonts scaled with body mass similarly to that in fish and ectotherms. We also calculate the curvature of the P 1 platform surface using the Dirichlet normal energy (DNE) as a proxy for diet. DNE values increase with body mass, supporting the assumption that conodont metabolic rates increased faster than mass 0.67 . We finally find that adults in both taxa differ in their food bases, which supports trophic diversification as an important driver of the remarkable disparity of conodont elements.

Insights for modern invasion ecology from biotic changes of the Clarksville Phase of the Richmondian Invasion (Ordovician, Katian)

Abstract: Abstract The frequency of biotic invasions in modern ecosystems is increasing due to global trade moving taxa outside their native ranges and climate change facilitating establishment of taxa in previously inhospitable regions. Thus, developing a holistic understanding of biotic invasions and how they impact ecosystems over different timescales—from annual to geologic timescales—is vital. Herein we examine a geologically brief invasion event, the Clarksville Phase of the Richmondian Invasion. Prior analyses have established general ecological and evolutionary patterns across the entire Richmondian Invasion, but recent sequence stratigraphic refinement makes analysis of individual invasion pulses possible for the first time. We examine biotic change across the Clarksville Phase and identify invasion impacts on diversity, paleocommunity composition, and niche stability. Invader arrival and success was strongly linked to increased propagule pressure facilitated by sea-level changes. Invaders initially colonized deep subtidal environments and then moved offshore facilitated by rapid niche evolution during the invasion interval. Invasive taxa that attained the largest population sizes belonged to previously underutilized ecological guilds. Overall, the introduction of the invasive taxa resulted in increased diversity that was maintained into the postinvasion interval accompanied by a change in community composition in which the invaders became dominant paleocommunity members. Combined, these analyses document a biotic invasion facilitated by climate change that increased local diversity through invaders occupying underutilized ecospace and competition-related niche contraction on millennial timescales. Developing a long-term perspective to accompany shorter-term studies facilitates predicting the long-term impacts of modern invasions and creating better-informed policies and practices.

Spatial distributions of Tribrachidium, Rugoconites, and Obamus from the Ediacara Member (Rawnsley Quartzite), South Australia

Abstract: The spatial distribution of in situ sessile organisms, including those from the fossil record, provides information about life histories, such as possible dispersal and/or settlement mechanisms, and how taxa interact with one another and their local environments. At Nilpena Ediacara National Park (NENP), South Australia, the exquisite preservation and excavation of 33 fossiliferous bedding planes from the Ediacara Member of the Rawnsley Quartzite reveals in situ communities of the Ediacara Biota. Here, the spatial distributions of three relatively common taxa, Tribrachidium, Rugoconites, and Obamus, occurring on excavated surfaces were analyzed using spatial point pattern analysis. Tribrachidium have a variable spatial distribution, implying that settlement or post-settlement conditions/preferences had an effect on populations. Rugoconites display aggregation, possibly related to their reproductive methods in combination with settlement location availability at the time of dispersal and/or settlement. Additionally, post-settlement environmental controls could have affected Rugoconites on other surfaces, resulting in lower populations and densities. Both Tribrachidium and Rugoconites also commonly occur as individuals or in low numbers on a number of beds, thus constraining possible reproductive strategies and environmental/substrate preferences. The distribution of Obamus is consistent with selective settlement, aggregating near conspecifics and on substrates of mature microbial mat. This dispersal process is the first example of substrate-selective dispersal among the Ediacara Biota, thus making Obamus similar to numerous modern sessile invertebrates with similar dispersal and settlement strategies.

History of Native American land and natural resource policy in the United States: impacts on the field of paleontology

Abstract: Abstract. 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).

Sediment-encased pressure–temperature maturation experiments elucidate the impact of diagenesis on melanin-based fossil color and its paleobiological implications

Abstract: Melanin pigments are central to colors and patterns in modern vertebrate integuments, which inform upon ecological and behavioral strategies like crypsis, aposematism, and sociosexual selection. Over the last decade, melanin has emerged as a valuable tool for predicting color in exceptionally preserved fossil feathers and subsequent testing of paleobiological hypotheses in long-extinct dinosaurs and birds. Yet much remains to be learned about melanin stability, diagenetic alterations to melanin chemistry, and their implications for “paleocolor reconstruction.” Pressure–temperature maturation experiments with modern feathers offer a way to examine these topics but have mostly been conducted in closed-system capsules or open-system aluminum foil. Both methods have operational limitations and do not consider the filtering effect of porous sediment matrices on thermally labile chemical groups versus stable ones during natural fossilization. We use sediment-encased maturation to resolve this issue and demonstrate replication of organic preservation of melanin highly comparable to compression fossils. Our experiments, coupled with time-of-flight secondary ion mass spectrometry, show predictable volatilization of N/S-bearing molecules and increased melanin cross-linking with elevated temperatures. We also suggest that eumelanin is more stable compared with pheomelanin at higher temperatures, explaining why eumelanic colors (black, dark brown, iridescent) are better preserved in fossils than pheomelanic ones (reddish brown). Furthermore, we propose that proteins preferentially undergo hydrolysis more so than forming N-heterocycles in selectively open systems analogous to natural matrices. Thus, we conclude that melanin pigments and not diagenetically altered protein remnants are the key players in promoting fossilization of soft tissues like feathers.

Blood flow rates to leg bones of extinct birds indicate high levels of cursorial locomotion

Abstract: Foramina of bones are beginning to yield more information about metabolic rates and activity levels of living and extinct species. This study investigates the relationship between estimated blood flow rate to the femur and body mass among cursorial birds extending back to the Late Cretaceous. Data from fossil foramina are compared with those of extant species, revealing similar scaling relationships for all cursorial birds and supporting crown bird–like terrestrial locomotor activity. Because the perfusion rate in long bones of birds is related to the metabolic cost of microfracture repair due to stresses applied during locomotion, as it is in mammals, this study estimates absolute blood flow rates from sizes of nutrient foramina located on the femur shafts. After differences in body mass and locomotor behaviors are accounted for, femoral bone blood flow rates in extinct species are similar to those of extant cursorial birds. Femoral robustness is generally greater in aquatic flightless birds than in terrestrial flightless and ground-dwelling flighted birds, suggesting that the morphology is shaped by life-history demands. Femoral robustness also increases in larger cursorial bird taxa, probably associated with their weight redistribution following evolutionary loss of the tail, which purportedly constrains femur length, aligns it more horizontally, and necessitates increased robustness in larger species.

PAB volume 49 issue 1 Cover and Front matter

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