Abstract Studies on paleophysiology and thermoregulation are central topics in fossil vertebrate paleobiology because they allow inferences about extinct organismal function beyond anatomical description. Pterosaur thermophysiology remains actively debated. Evidence such as relatively rapid growth and elevated metabolic rate estimates has been used to argue for endothermic-like physiologies consistent with the energetic demands of powered flight, whereas reproductive traits, including burial incubation and precocial development, have led some authors to propose ectothermic strategies more akin to those of extant non-avian diapsids. Here, we provide quantitative estimates of resting metabolic rate (RMR) for the tapejarid pterosaur Caiuajara dobruskii using phylogenetic eigenvector maps and osteocyte lacunar density as proxy. Analysis of six histological sections from three appendicular elements (femur, tibia, humerus) at different ontogenetic stages (adult and juvenile) yielded mass-independent RMR estimates of 0.24–0.76 ml O 2 h −1 g −0.86 , substantially higher than those of lepidosaurs but lower than typical mammalian and avian values. The retrodicted mass-independent maximum metabolic rate (MMR) of 5.68 ml O 2 h −1 g −0.87 falls between values for highly active reptiles and birds, suggesting sufficient aerobic capacity to sustain powered flight without fully matching the maximal performance of small endotherms. Together, these results suggest active-flighted pterosaurs fall among a metabolically intermediate continuum, limiting straightforward actualistic comparisons for inferring their thermoregulatory strategy.
We use new macroevolutionary rate estimates to resolve the dynamics of severe versus background extinction through the history of a major, globally distributed, Paleozoic zooplankton clade, the graptoloids. Our data span one of the "Big Five" mass extinctions, the Late Ordovician Mass Extinction (LOME), and several secondary, severe extinction events. We use cohort survivorship curves to derive both "instantaneous" rates and smoothed rates based on "natural" time-bin intervals that honor the structure of the data. We avoid the approximation of many approaches that average rate estimates within essentially arbitrary time bins.We find that 63% of graptoloid extinctions lie within intervals classified previously as "background" extinction; only 7% lie within the LOME, and the remainder lie within the spans of 15 other secondary extinction events spread through the Ordovician and Silurian. Extinction rate magnitudes define a continuous, unimodal distribution. Background extinction in the graptoloids is not stochastically uniform but includes many more high-rate pulses than expected under a null model of uniform, memoryless extinction. Our results support the inference of pulsed extinction in the marine realm, with pulses occurring on timescales much finer than the standard age divisions of the Ordovician and Silurian periods. The LOME and secondary extinction events are not characterized by instantaneous extinction rates that are higher than so-called background. Instead, extinction events are distinguished from background by increased duration of their component, short-lived pulses of elevated extinction, and the LOME represents a protracted interval with multiple such pulses and little time for faunal recovery.Our results are consistent with the notion that, whereas a mass or severe extinction may have an exceptional or singular initial trigger, the effects of that trigger propagate out to global-scale species loss via a complex web of processes that are common to many extinction episodes and may take significant time.
Wing shape is integrally related to flight performance and function in extant animals. Analyzing this relationship in pterosaurs is complicated by the fragmentary nature of the fossil record and because the flight dimensions of wing membranes do not preserve. In the absence of fully extended pterosaur wing fossils, scientific reconstruction of the pterosaur Bauplan presents the clearest alternative for analysis. However, these wing shapes are subject to multiple conflicting scientific opinions and the artistic styles of the researchers and illustrators reconstructing them. Here we test the functional ramifications of different wing-shape reconstructions. We use theoretical morphospace analysis to establish whether modern reconstructions of pterosaur wings exhibit the diversification and functional performance expected of living animals. Pterosaur wing reconstructions show little by way of taxonomic separation either in shapespace or functional performance, with all pterosaur groups overlapping independent of time, size or proposed niche. This suggests that published pterosaur reconstructions underestimate the diversity of wing shapes expected of such a diverse group and are not reflective of flying animals. Stylistic approaches have little effect on the occupation and diversity of pterosaur reconstructions, suggesting that the underpinning issues lie in the lack of scientific consensus on the shape and structure of the wings, rather than how they are reconstructed.
The chances that existing taxa are replaced by new taxa decreases over Phanerozoic time, and older taxa persist for longer and longer. This long-term trend has been interpreted as resulting from repeated culling and non-replacement of groups with high turnover or, in other words, from long-term selection for extinction resistance. It is therefore assumed that taxon-specific properties are critical for this trend. However, taxa are part of higher-level ecological genealogical units that represent shared genealogies and histories of ecological interactions. Structural aspects such as the composition of the evolving eco-genealogical units as a possible explanation have received little attention. Here we analyzed the temporal change within Phanerozoic benthic marine mega-assemblages (PMAs). PMAs are groups of marine animal genera delineated through hierarchical modular partitioning of a multilayer spatiotemporal network and interpreted as eco-genealogical units. For each higher-level PMA, we calculated how its median genus age, its richness, the evolutionary rates, and the spatial beta-diversity changed over time. The resulting estimates support the assumption that the assemblages are meaningful eco-evolutionary units, because their temporal patterns differ from those of randomly chosen Phanerozoic time intervals. PMAs differ from randomly chosen intervals in that the increase of genus age is associated with a decline in origination proportions and with increasing beta-diversities. This contradicts the hypothesis of a simple Phanerozoic sorting toward extinction resistance and generalization. The observed pattern can be explained as a process of eco-evolutionary entrenchment resulting from conditioned assembly and weak within-lineage directionality toward specialization and geographic restriction.
Sister groups (two clades sharing a common ancestor) often differ greatly in taxonomic, phenotypic, and ecologic diversity, but explanations for these differences remain elusive. One hypothesis is that mate choice involving display promotes genetic isolation and thus speciation. We test this and other hypotheses by analyzing individual-level phenotypes that evolved in one but not the other of the two great molluscan sister clades Aculifera (chitons and relatives) and the much more diverse Conchifera (snails, clams, squid, and their relatives). The key difference lies in the morphological relationship between body and shell, which in Aculifera are tightly coupled, greatly limiting locomotion, activity, and mate choice. In Conchifera (especially in the major subclade Megalopodifera), the body and shell are more decoupled, facilitating a wide range of activity, modular evolution, and ecological expansion. Contrary to the primacy of mate choice as an engine of diversification, display-related mate choice is part of a larger theme of evolutionary feedbacks among habitat (including mate) choice, locomotor and other activity, and speciation. Some conchiferan clades never diversified and remain phenotypically conservative, highlighting the fact that the only unifying feature of a clade is its retrospective monophyly.
Traditional approaches to studying paleontological biodiversity have focused on richness, that is, the number of taxa at a given level in the Linnaean hierarchy. While valuable, this approach does not capture the phylogenetic dimension of biodiversity as reflected by its taxonomic structure. This paper introduces a novel perspective in the study of past biodiversity by applying taxonomic distinctness (TD) metrics, average taxonomic distinctness (AvTD) and variation in taxonomic distinctness (VarTD), to investigate the rediversification of marine bivalves following the Permian-Triassic mass extinction. Using a dataset of 59 fossil faunas, we explore the dynamics of the taxonomic tree during the Triassic and along paleolatitudinal gradients. Subtropical assemblages show higher AvTD and lower VarTD than tropical ones, suggesting ecological and biogeographic influences on the taxonomic structure. In the temporal dimension, our data reveal an Early Triassic decrease in AvTD and an increase in VarTD, followed by a long-term trend of increasing AvTD and decreasing VarTD that persisted until the Norian. This pattern suggests that vacant ecospace after the end-Permian mass extinction did not stimulate the immediate appearance of a disproportional number of supraspecific taxa, possibly due to the unusual biotic and abiotic environment of the early postextinction time. In contrast, the long-term increase in AvTD that followed this Early Triassic lag phase indicates a low but steady surplus of supraspecific taxa relative to newly evolved species. This observation supports macroevolutionary scenarios in which evolutionary rates correlate with ecological opportunity. However, the long duration of this phase is unexpected, particularly when compared with conventional indicators for "complete" recovery. Based on TD metrics, recovery from the greatest Phanerozoic mass extinction went on at least until the end of the Norian, nearly 50 Ma after the crisis.
Sauropodomorphs were the largest terrestrial animals to have ever existed on Earth.While previous studies using skeletal remains and digital 3D models suggested that manus became more circular shape and relatively larger over time, this study uses trackways to test these hypotheses with a much larger sample size. In this study, we used the sauropodomorph trackway record from the Early Jurassic to the Late Cretaceous to analyze temporal changes in manus and pes shapes and their relationship with body size. We analyzed footprint measurements from 690 trackways and, for the first time, applied elliptic Fourier descriptors (EFDs) to sauropodomorph footprint outlines to quantitatively assess their morphology. Analyses revealed temporal and size-related changes in manus morphology, whereas no changes were observed in pedes. Specifically, manus shape became anteroposteriorly longer over time and in larger individuals. The relative manus area compared with pes area (the heteropody) also increased chronologically; however, manus areas showed negative allometry relative to pes areas. These results indicate that the temporal change toward circular or horseshoe-shaped manus morphology in sauropodomorphs represents an adaptation to gigantism, while the chronological increase in manus size relative to the pes reflects the radiation of a clade (Titanosauria) with proportionally large manus.
The mammalian skull plays important roles in sensing, communication, and obtaining and processing food. These diverse functions make the skull a natural target for investigating how developmental processes and selective pressures related to ecology interact to produce patterns of morphological evolution. Here, we investigate the evolution of the equid skull through the lens of craniofacial evolutionary allometry (CREA), a pattern of relative facial elongation in larger mammals that has been hypothesized to result from similar patterns of facial elongation over ontogeny. Using 3D geometric morphometrics and linear measurements, we describe the major axes of shape variation in the equid skull, test whether equids follow or deviate from the CREA pattern over the clade's evolutionary history, and assess whether the evolution of high-crowned teeth (hypsodonty) is related to relative facial proportions, all in an explicitly phylogenetic context. We find that equids deviate from the CREA pattern and that the evolution of hypsodont dentition did not significantly influence facial proportions in the group. Importantly, these results are only apparent when using statistics appropriate for phylogenetic data. Comparison with previously published data on facial proportions from modern equids indicates that ontogenetic patterns of facial elongation do not scale to produce patterns of facial proportions observed at the intraspecific and evolutionary levels. Taken together, our results complicate the historic narrative that a single set of selective factors drove patterns of morphological evolution within the group.
The fossil record offers a unique window into patterns of extinction and biodiversity recovery over deep time, and recent advances in analytical methods have significantly enhanced this research field. Our analysis of an updated dataset that includes 50 terminal taxa and 175 fossil occurrences of Ophiacodontidae, Edaphosauridae, and Sphenacodontidae (OES grade hereafter) using a recent implementation of the skyline fossilized birth-death model (FBD hereafter) confirms our previous conclusion that the OES grade diversified during the latter half of the Pennsylvanian but waned thereafter. However, our new results differ in several important points compared with our previous study (published in 2024). Notably, the transition between these two diversification regimes seems to have occurred earlier (at 298.9 Ma, at the Carboniferous/Permian transition), and it appears to have been marked by a moderate (0.527 survival probability), previously unreported extinction event. Also, the OES grade seems to have experienced a much more severe mass extinction event in the mid-Kungurian, with an estimated survival rate of only 0.113, which left very few surviving OES grade lineages. Climatic instability that started around the Carboniferous/Permian boundary and lasted throughout the Cisuralian, plausibly caused by intense volcanism of the Tarim Large Igneous Province and the Panjal Traps, may explain this pattern, which consists of a stagnating biodiversity followed by a brief, severe extinction event. This is reminiscent of the press-pulse model proposed by Arens and West in 2008, but if there was indeed an end-Carboniferous crisis, it could also be viewed as a new, more complex, pulse-press-pulse pattern.
Abelisaurid dinosaurs display a remarkable diversity in cranial ornamentation, which includes several features such as rugosities, pits and grooves on the rostrum and orbital regions, midline knobs, and paired plus sculptured structures across the skull roof. To investigate macroevolutionary patterns that underlie this diversity, we tested the "species recognition" hypothesis using phylogenetic comparative methods. Our results indicate directional and ordered evolutionary patterns in cranial ornamentation that are more consistent with expectations of sexual selection than with the stochastic patterns predicted under the species recognition hypothesis. Moreover, sympatric species exhibited highly divergent ornamentation, and the degree of surface texturing and the development of certain structures (e.g., knobs) increased through ontogeny. These findings suggest that cranial ornamentation in Abelisaurids was influenced by mechanisms of sexual selection, sexual dimorphism, or mutual selection. Evolutionary modeling combined with evidence from the fossil record and phylogenetic correlation analysis reveals that the ornamentation of the rostrum and orbital regions was evolutionarily coupled and became canalized during the Early Cretaceous. In contrast, phylogenetic correlation analyses demonstrated that skull roof ornaments and rostral and orbital ornaments evolved decoupled. Neither discrete ornament traits nor the accumulation of traits over time showed significant associations with body size, indicating that ornament diversification in Abelisauridae was not constrained by allometric trends. During the Late Cretaceous, after refined ecological specialization, the subclades Carnotaurini and Majungasaurinae underwent further elaboration, acquiring features such as a prominent midline knobs, paired structures, and reinforced occipital and cervical regions. These derived morphologies may have facilitated more complex sociosexual behaviors.
The fossil record is subject to multiple biases that can distort macroevolutionary and paleoecological inferences. Although temporal and spatial sampling biases have received substantial attention, other sources of fossil sampling heterogeneity remain less well quantified. Using the Triton database of planktonic foraminifera, we assess the influence of geographic, ecological, morphological, and methodological factors on fossil recovery rates. We first apply a temporal subsampling method to standardize fossil occurrences over geologic time, validating this approach against an expert-curated lineage-through-time trajectory. After subsampling, the occurrences remain unevenly distributed throughout species' lifetimes and inhomogeneously distributed across species, reflecting biological signal and/or persistent sampling biases.We then investigate this residual sampling heterogeneity with a generalized additive model incorporating relevant predictors from Triton. Our results reveal that, after correcting for temporal biases, geographic predictors (paleolatitude, paleolongitude, longitudinal spread) explain nearly a third of sampling variation. Species-specific ecological and morphological attributes contribute an additional fraction, among which mean relative abundance emerges as the main factor. Additional predictors of fossil sampling rates include age-calculation methods and biostratigraphic sampling biases. Despite accounting for multiple sources of variation, 37% of the deviance remains unexplained, suggesting unmodeled biological, stratigraphic, diagenetic, or taxonomic drivers of sampling heterogeneity.Overall, observed recovery rates question the validity of the homogeneous-sampling assumption used in most diversification models, and this heterogeneity cannot be reduced to a single dominant factor. This conclusion reinforces the need for integrated subsampling approaches and process-based models that explicitly account for heterogeneous fossilization rates to improve the reliability of macroevolutionary analyses.
Digenean trematodes are parasites with a complex life cycle that often infest shell-bearing mollusks and produce distinct traces on the host skeleton that are recognizable in the fossil record. Here, three bivalve species (Transennella conradina, Abra segmentum, and Chamelea gallina) from Pleistocene and Holocene deposits of Florida and Italy were used to evaluate the hypothesis that trematode infestation affects shell morphology. The morphological effects of infestation were evaluated using geometric morphometrics and the pallial sinus index (PSI = pallial sinus length/shell length). For all three host species: (1) large size classes possess higher trematode prevalence (i.e., proportion of specimens possessing trematode-induced pits within a population) and higher per-specimen frequency of trematode-induced scars when compared with smaller size classes, suggesting ontogenetic accumulation of parasites; and (2) infested and non-infested specimens significantly differ in shell landmark-based morphology. Geometric morphometric analyses indicate that in two out of three species (Transennella conradina, Abra segmentum): (1) PSI and thin-plate spline analyses suggest significant pallial sinus reduction in infested specimens relative to non-infested; and (2) overall morphospace range, estimated by sample-standardized principal component (PC) hypervolume, was inflated with the inclusion of infested specimens. Consistent with previous studies, results indicate that trematode-induced morphological changes may influence the burrowing capabilities of the studied bivalves, affecting their ecological functioning and fitness. Changes in morphospace induced by trematode parasites hamper species delineation and confound morphometric and disparity patterns in the fossil record of infestation-prone species. Excluding fossil specimens with trematode traces can mitigate those confounding effects. Conversely, comparative morphometric analyses of infested and non-infested host specimens may allow us to investigate host responses to parasites over evolutionary timescales.
The Lilliput Effect, wherein assemblages decrease in mean individual body size after mass extinctions, has not been documented at a wide geographic scale in any of the Late Devonian mass extinction pulses in invertebrate taxa. Based on a dataset of 800 scolecodonts (polychaete jaw elements) from the literature, museum collections, and newly presented data from the Appalachian Basin, we find that scolecodont size distribution per temporal bin decreases across the Frasnian/Famennian Kellwasser Events from a median length of 500 mu m before the Kellwasser Events to a median length of 196 mu m during the Kellwasser Events. The majority of the small scolecodonts documented during the extinction interval are newly measured specimens from the Kellwasser Events of the Appalachian Basin, although this size change is not unique to the Appalachian Basin. We interpret the reduction in body size as a hypoxia-driven occurrence of the Lilliput Effect because of the susceptibility of benthic invertebrates to hypoxia and the association of this extinction event with hypoxia. While previous studies have shown that polychaete community biomass decreases in response to oxygen stress, our study provides fossil evidence of individual size reduction, plausibly due to oxygen stress.
With the growing application of artificial intelligence (AI) and machine learning (ML), great potential exists to leverage these technologies in paleontology. Relative to many other scientific fields, a challenge of ML applied to paleontology is small sample sizes, particularly for fossil vertebrates. Shark teeth, abundant in the fossil record, provide a model system to use ML across varying sample sizes. Here we use six classes (taxa) of Neogene shark teeth for taxonomic identification, including a curated dataset of 3150 images. Each class was evaluated using an 80% training and 20% validation split, with a separate, external test set of 25 samples per class. Pretrained models perform well (accuracy > 90%), providing a strong baseline for classification. However, enabling fine-tuning of the ML model to identify fossil shark teeth improves performance considerably. Likewise, sample size per class also affects the accuracy of the models' classifications. Smaller sample sizes (n = 50 individuals per class) yielded a mean accuracy of 93.4%, but plateaued at similar to 99% between 200 and 500 images per class. Confidence likewise increases with larger samples, from 81.8% (n = 50 individuals per class) to >90% (n = 300 to 500 individuals per class). Misidentifications followed consistent patterns, reflecting morphological similarities and/or poor preservation. Artificially increasing the training datasets using data augmentation improves the confidence of identifications. This research indicates that relatively small samples of vertebrate species (similar to 50 to 500 individuals per class) can effectively train an ML model to identify these shark teeth with high levels of accuracy.
Over the past 10 million years, coastal-marine settings along the Peruvian Margin have undergone profound geographic and oceanographic transformations, resulting in extensive changes in coastal-marine communities. While mollusk taxonomy research is slowly being integrated into ecosystem-wide analyses, which have historically centered on vertebrates, a long-term chronostratigraphically controlled analysis of molluscan diversity and compositional changes has not been undertaken for this region. We compiled a database covering 152 species, 97 genera, and 51 families of mollusk fossils from the Peruvian Margin (13-16 degrees S) to assess long-term diversification patterns and faunal turnover from the late Miocene to the present. We identified two distinctive molluscan assemblages. The first, dating to the late Miocene (10-6 Ma), underwent a substantial shift during the Mio-Pliocene transition (6-4 Ma), culminating in a second assemblage more akin to modern counterparts. This shift resulted in an increase in diversity, with the younger assemblage (6-0 Ma) exhibiting greater genus richness than the former late Miocene assemblage. The turnover at 6-4 Ma was driven by peaks in bivalve origination (6-5 Ma) along with elevated extinction rates for gastropods (6-5 Ma) and bivalves (5-4 Ma). Ecological analyses revealed that no single ecological trait consistently changed during this interval, indicating that the turnover resulted from a broad reorganization of ecological strategies. We propose that the major molluscan turnover during the late Miocene-early Pliocene is associated with geomorphological changes related to the Andean uplift, the disappearance of semi-embayments, and a sea-level rise.
Sexual dimorphism, a widespread phenomenon, has been extensively researched in extant and fossil crustaceans. However, identifying sexual dimorphism in phyllocarid fossils preserved as isolated parts is often challenging, except in cases where the specimens are exceptionally well preserved, including those with soft tissues. This study proposes a novel approach by introducing the use of geometric morphometric techniques to identify sexual dimorphism in phyllocarid fossils based on carapace morphology. It presents a comprehensive re-analysis of Soomicaris ordosensis Liu et al., 2023a, carapaces from the Upper Ordovician in North China and Tarim Plates. Elliptic Fourier analysis was applied to quantify the size and shape variation in nearly 100 specimens. The results demonstrate the presence of significant sexual dimorphism in the length and shape of the S. ordosensis carapace. The carapace shape exhibited variation between the sexes: the posterodorsal margin of one group of carapaces gradually extends backward to form a posterodorsal spine; the carapaces of the other group have a convex posterior margin and lack a posterodorsal spine. Additionally, both types manifest an overall allometric growth pattern, albeit with distinct growth coefficients. Furthermore, the observed approximately 1:1 ratio between the two forms suggests that the population of S. ordosensis may have exhibited a dioecious mating system. Geometric morphometrics are a highly effective method for elucidating the subtle variations in the carapace morphology of S. ordosensis, thereby underscoring the cryptic dimorphism characteristics of fossil animals. This finding offers the first indirect evidence for egg-brooding behavior within the extinct order Archaeostraca.
An important question in evolutionary biology and macroecology is whether taxa show systematic trajectories in occupancy, the proportion of geographic area occupied, over macroevolutionary timescales. Past studies have used fossils to document these trajectories, showing a symmetric rise and fall. In this study, I focus on several biases in the analyses of fossil occupancy trajectories that have been unaccounted for. First, better sampling of boundary bins in a taxon's stratigraphic range, paradoxically, results in lower mean occupancy of taxa in those bins. This is because better sampling allowed more taxa with low occupancies to be included in the mean occupancies of those bins compared with intermediate bins. Second, the possibility that taxa may have incomplete durations within boundary bins could also lower occupancies in those bins. Finally, a bias can also exist when the number of sampled sites is not constant throughout a taxon's stratigraphic range. I use simulations to show that the first bias can be corrected by conditioning these boundary bins to be sampled in the same way as intermediate bins. To mitigate the second bias, I use higher-resolution time bins to constrain the intervals over which taxa's occupancies are measured so that they are comparable between boundary and intermediate time bins. I also present an approach that can correct for the last bias by subsampling geographic sites, testing its impact in a simulation. Considering these factors, the occupancy trajectories of marine animal genera look to be a relatively gradual rise post-origination with a sudden decline before extinction.
Richard Bambach was a leading figure in the "paleobiology revolution" of the late 1960s and 1970s, keeping the movement grounded with his keen geological and ecological insights. With interests ranging from the functional biology of individual organisms to the largest macroevolutionary trends in the history of life, he was especially adept at linking paleoecological and macroevolutionary patterns across spatiotemporal scales. He authored seminal publications during five different decades and was recognized with both the Moore Medal from the Society for Sedimentary Geology and the Paleontological Society Medal.
The patterns by which ancestral species give rise to descendants offer critical insights into the processes governing evolutionary and ecological change through time. One such pattern, predicted by both theoretical models and empirical studies, is the persistence of long-lived ancestral species that give rise to multiple descendants. While models such as the birth-death process long employed by paleobiologists predict the occurrence of such "super-progenitors," the extent to which they should appear in fossil clades remains unknown. To address this, I apply a birth-death-sampling model to four marine clades to evaluate the expected prevalence of super-progenitors and the distribution of sampled descendants. I also explore through analytical and simulation-based predictions how variation in preservation, turnover, and net diversification rate influences these expectations. The model predicts that super-progenitors should be common across nearly all of the clades examined, provided that sampling completeness exceeds approximately 50% at the taxon level. Although the threshold excludes some poorly sampled terrestrial groups, my findings suggest that super-progenitors should be expected across a broad array of clades. Continued integration of super-progenitors into phylogenetic inference and models of diversification may thus contribute to a more complete understanding of macroevolutionary pattern and process.
Bones preserved in fluvial sediments make up the majority of the terrestrial vertebrate fossil record, and unsteady flows (overbank floods, levee breaches, debris flows, etc.) are often invoked as agents of bone transport and burial. Experiments exploring transport of mammal bones under steady-state flow led to the development of Voorhies Groups, which are used as indicators of winnowing and transport at fossil sites. Some studies have raised concerns about the use of transport groups beyond the scope of the original experiments, especially regarding untested taxa and flow conditions. Here we investigate transport of hadrosauroid dinosaur bone models and modern sheep bones in experimental sheet floods. We find that evolving flow dynamics in unsteady flows can influence bone mobility behaviors. Factors such as bedforms and interactions with other bones caused shorter transport distances than might be expected in some elements, which would be heightened in real flooding situations where trapping mechanisms are common. Our hadrosauroid bones sorted into two statistically significant groups and one overlapping intermediate group based on transport distance. However, those groups could not be identified among sheep bones. Distributions of transport distances in both taxa do not fully match predictions based on Voorhies Groups. Our results indicate that Voorhies Groups do not quantitatively apply to all potential fluvial settings and taxa, and we thus advise caution in interpretations of fossil site taphonomic history based on Voorhies Groups. Further exploration of variables underlying bone transport and burial may allow for more broadly comparative examinations of fluvial biostratinomy.
