Showing papers in "Paleobiology in 2017"

Recognizing sexual dimorphism in the fossil record: lessons from nonavian dinosaurs

Abstract: The demonstration of sexual dimorphism in the fossil record can provide vital information about the role that sexual selection has played in the evolution of life. However, statistically robust inferences of sexual dimorphism in fossil organisms are exceedingly difficult to establish, owing to issues of sample size, experimental control, and methodology. This is particularly so in the case of dinosaurs, for which sexual dimorphism has been posited in many species, yet quantifiable data are often lacking. This study presents the first statistical investigation of sexual dimorphism across Dinosauria. It revisits prior analyses that purport to find quantitative evidence for sexual dimorphism in nine dinosaur species. After the available morphological data were subjected to a suite of statistical tests (normality and unimodality tests and mixture modeling), no evidence for sexual dimorphism was found in any of the examined taxa, contrary to conventional wisdom. This is not to say that dinosaurs were not sexually dimorphic (phylogenetic inference suggests they may well have been), only that the available evidence precludes its detection. A priori knowledge of the sexes would greatly facilitate the assessment of sexual dimorphism in the fossil record, and it is suggested that unambiguous indicators of sex (e.g., presence of eggs, embryos, medullary bone) be used to this end.

Dietary responses of Sahul (Pleistocene Australia-New Guinea) megafauna to climate and environmental change

Abstract: . Throughout the late Quaternary, the Sahul (Pleistocene Australia—New Guinea) vertebrate fauna was dominated by a diversity of large mammals, birds, and reptiles, commonly referred to as megafauna. Since ca. 450–400Ka, approximately 88 species disappeared in Sahul, including kangaroos exceeding 200 kg in size, wombat-like animals the size of hippopotamuses, flightless birds, and giant monitor lizards that were likely venomous. Ongoing debates over the primary cause of these extinctions have typically favored climate change or human activities. Improving our understanding of the population biology of extinct megafauna as more refined paleoenvironmental data sets become available will assist in identifying their potential vulnerabilities. Here, we apply a multiproxy approach to analyze fossil teeth from deposits dated to the middle and late Pleistocene at Cuddie Springs in southeastern Australia, assessing relative aridity via oxygen isotopes as well as vegetation andmegafaunal diets using both car...

Comparing cal3 and other a posteriori time-scaling approaches in a case study with the pterocephaliid trilobites

Abstract: . Reconstructing the tree of life involvesmore than identifying relationships among lineages; it also entails accurately estimating when lineages diverged. Paleontologists typically scale cladograms to time a posteriori by direct reference to first appearances of taxa in the stratigraphic record. Some approaches use probabilistic models of branching, extinction, and sampling processes to date samples of trees, such as the recently developed cal3 method, which stochastically draws divergence dates given a set of rates for those processes. However, these models require estimates of the rates of those processes, which may be hard to obtain, particularly for sampling. Here, we contrast the use of cal3 and other a posteriori time-scaling approaches by examining a previous study that documented a decelerating rate of morphological evolution in pterocephaliid trilobites. Although aspects of the data set make estimation of branching, extinction, and sampling rates difficult, we use a multifaceted approach...

Relating Ediacaran Fronds

Abstract: Ediacaran fronds are key components of terminal-Proterozoic ecosystems. They represent one of the most widespread and common body forms ranging across all major Ediacaran fossil localities and time slices postdating the Gaskiers glaciation, but uncertainty over their phylogenetic affinities has led to uncertainty over issues of homology and functional morphology between and within organisms displaying this ecomorphology. Here we present the first large-scale, multigroup cladistic analysis of Ediacaran organisms, sampling 20 ingroup taxa with previously asserted affinities to the Arboreomorpha, Erniettomorpha, and Rangeomorpha. Using a newly derived morphological character matrix that incorporates multiple axes of potential phylogenetically informative data, including architectural, developmental, and structural qualities, we seek to illuminate the evolutionary history of these organisms. We find strong support for existing classification schema and devise apomorphy-based definitions for each of the three frondose clades examined here. Through a rigorous cladistic framework it is possible to discern the pattern of evolution within and between these clades, including the identification of homoplasies and functional constraints. This work both validates earlier studies of Ediacaran groups and accentuates instances in which previous assumptions of their natural history are uninformative.

Completeness of the eutherian mammal fossil record and implications for reconstructing mammal evolution through the Cretaceous/Paleogene mass extinction

Abstract: There is a well-established discrepancy between paleontological and molecular data regarding the timing of the origin and diversification of placental mammals. Molecular estimates place interordinal diversification dates in the Cretaceous, while no unambiguous crown placental fossils have been found prior to the end-Cretaceous mass extinction. Here, the completeness of the eutherian fossil record through geological time is evaluated to assess the suggestion that a poor fossil record is largely responsible for the difference in estimates of placental origins. The completeness of fossil specimens was measured using the character completeness metric, which quantifies the completeness of fossil taxa as the percentage of phylogenetic characters available to be scored for any given taxon. Our data set comprised 33 published cladistic matrices representing 445 genera, of which 333 were coded at the species level.Therewas no significant difference in eutherian completeness across the Cretaceous/Paleogene (K/Pg) boundary. This suggests that the lack of placental mammal fossils in the Cretaceous is not due to a poor fossil record but more likely represents a genuine absence of placental mammals in the Cretaceous. This result supports the “explosivemodel” of early placental evolution, whereby placentalmammals originated around the time of the K/Pg boundary and diversified soon after.No correlation was found between the completeness pattern observed in this study and those of previous completeness studies on birds and sauropodomorph dinosaurs, suggesting that different factors affect the preservation of these groups. No correlations were found with various isotope proxy measures, but Akaike information criterion analysis found that eutherian character completeness metric scores were best explained by models involving the marine-carbonate strontium-isotope ratios (87Sr/86Sr), suggesting that tectonic activity might play a role in controlling the completeness of the eutherian fossil record.

Spatially Explicit Analysis Sheds New Light on the Pleistocene Megafaunal Extinction in North America

Abstract: The late Pleistocene megafaunal extinctions may have been the first extinctions directly related to human activity, but in North America the close temporal proximity of human arrival and the Younger Dryas climate event has hindered efforts to identify the ultimate extinction cause. Previous work evaluating the roles of climate change and human activity in the North American megafaunal extinction has been stymied by a reliance on geographic binning, yielding contradictory results among researchers. We used a fine-scale geospatial approach in combination with 95 megafaunal last-appearance and 75 human first-appearance radiocarbon dates to evaluate the North American megafaunal extinction. We used kriging to create interpolated first- and last-appearance surfaces from calibrated radiocarbon dates in combination with their geographic autocorrelation. We found substantial evidence for overlap between megafaunal and human populations in many but not all areas, in some cases exceeding 3000 years of predicted overlap. We also found that overlap was highly regional: megafauna had last appearances in Alaska before humans first appeared, but did not have last appearances in the Great Lakes region until several thousand years after the first recorded human appearances. Overlap in the Great Lakes region exceeds uncertainty in radiocarbon measurements ormethodological uncertainty and would be even greater with sampling-derived confidence intervals. The kriged maps of last megafaunal occurrence are consistent with climate as a primary driver in some areas, but we cannot eliminate human influence from all regions. The late Pleistocene megafaunal extinction was highly variable in timing and duration of human overlap across the continent, and future analyses should take these regional trends into account.

Craniodental functional evolution in sauropodomorph dinosaurs

Abstract: Sauropodomorpha included the largest known terrestrial vertebrates and was the first dinosaur clade to achieve a global distribution. This success is associated with their early adoption of herbivory, and sauropod gigantism has been hypothesized to be a specialization for bulk feeding and obligate high-fiber herbivory. Here, we apply a combination of biomechanical character analysis and comparative phylogenetic methods with the aim of quantifying the evolutionary mechanics of the sauropodomorph feeding apparatus. We test for the role of convergence to common feeding function and divergence toward functional optima across sauropodomorph evolution, quantify the rate of evolution for functional characters, and test for coincident evolutionary rate shifts in craniodental functional characters and body mass. Results identify a functional shift toward increased cranial robustness, increased bite force, and the onset of static occlusion at the base of the Sauropoda, consistent with a shift toward bulk feeding. Trends toward similarity in functional characters are observed in Diplodocoidea and Titanosauriformes. However, diplodocids and titanosaurs retain significant craniodental functional differences, and evidence for convergent adoption of a common “adaptive zone” between them is weak. Modeling of craniodental character and body-mass evolution demonstrates that these functional shifts were not correlated with evolutionary rate shifts. Instead, a significant correlation between body mass and characters related to bite force and cranial robustness suggests a correlated-progression evolutionary mode, with positive-feedback loops between body mass and dietary specializations fueling sauropod gigantism.

Herbivorous dinosaur jaw disparity and its relationship to extrinsic evolutionary drivers

Abstract: Morphological responses of nonmammalian herbivores to external ecological drivers have not been quantified over extended timescales. Herbivorous nonavian dinosaurs are an ideal group to test for such responses, because they dominated terrestrial ecosystems for more than 155 Myr and included the largest herbivores that ever existed. The radiation of dinosaurs was punctuated by several ecologically important events, including extinctions at the Triassic/Jurassic (Tr/J) and Jurassic/Cretaceous (J/K) boundaries, the decline of cycadophytes, and the origin of angiosperms, all of which may have had profound consequences for herbivore communities. Here we present the first analysis of morphological and biomechanical disparity for sauropodomorph and ornithischian dinosaurs in order to investigate patterns of jaw shape and function through time. We find that morphological and biomechanical mandibular disparity are decoupled: mandibular shape disparity follows taxonomic diversity, with a steady increase through the Mesozoic. By contrast, biomechanical disparity builds to a peak in the Late Jurassic that corresponds to increased functional variation among sauropods. The reduction in biomechanical disparity following this peak coincides with the J/K extinction, the associated loss of sauropod and stegosaur diversity, and the decline of cycadophytes. We find no specific correspondence between biomechanical disparity and the proliferation of angiosperms. Continual ecological and functional replacement of pre-existing taxa accounts for disparity patterns through much of the Cretaceous, with the exception of several unique groups, such as psittacosaurids that are never replaced in their biomechanical or morphological profiles.

Horses in the cloud; big data exploration and mining of fossil and extant Equus (Mammalia, Equidae)

Abstract: . Extant species of the genus Equus (e.g., horses, asses, and zebras) have a widespread distribution today on all continents except Antarctica. Extinct species of Equus represented by fossils were likewise widely distributed in the Pliocene and even more so during the Pleistocene. In order to understand the efficacy of “big data” for (paleo)biogeographic analyses, location records (latitude, longitude) and fossil occurrences for the genus Equus were mined and further explored from six databases, including iDigBio, Paleobiology Database, VertNet, BISON, Neotoma, and GBIF. These were chosen from a priori knowledge of where relevant data might be aggregated. We also realized that these databases have different objectives and data sources and therefore would provide a useful comparative study of the widespread taxon Equus in space and time. The mining of Equus data from these six sources yielded a combined total of 123.8 K location records, including 116.2K fossil specimens. These include individual p...

Inferring flight parameters of Mesozoic avians through multivariate analyses of forelimb elements in their living relatives

Abstract: . Our knowledge of the diversity, ecology, and phylogeny of Mesozoic birds has increased significantly during recent decades, yet our understanding of their flight competence remains poor. Wing loading (WL) and aspect ratio (AR) are two aerodynamically relevant parameters, as they relate to energy costs of aerial locomotion and flight maneuverability. They can be calculated in living birds (i.e., Neornithes) from body mass (BM), wingspan (B), and lift surface (SL). However, the estimates for extinct birds can be subject to biases from statistical issues, phylogeny, locomotor adaptations, and diagenetic compaction. Here we develop a sequential approach for generating reliable multivariate models that allow estimation of measurements necessary to determine WL and AR in the main clades of non-neornithine Mesozoic birds. The strength of our predictions is supported by the use of those variables that show similar scaling patterns in modern and stem taxa (i.e., non-neornithine birds) and the similarity ...

Assessing niche conservatism using a multiproxy approach: dietary ecology of extinct and extant spotted hyenas

Abstract: A central premise of bioclimatic envelope modeling is the assumption of niche conservatism. Whereas such assumptions are testable in modern populations, it is unclear whether niche conservatism holds over deeper time spans and over very large geographic ranges. Hyaenids occupied a diversity of ecological niches over time and space, and until the end-Pleistocene they occurred in Europe and most of Asia, with Asian populations of Crocuta suggested as being genetically distinct from their closest living relatives. Further, little is known regarding whether and how the dietary ecology of extinct populations of Crocuta differed from those of their extant African counterparts. Here, we use a multiproxy approach to assess an assumption of conserved dietary ecology in late Pleistocene extant spotted hyenas via finite element analysis, dental microwear texture analysis, and a novel dental macrowear method (i.e., whether teeth are minimally, moderately, or extremely worn, as defined by degree of dentin exposure) proposed here. Results from finite element simulations of the masticatory apparatus of Chinese and African Crocuta demonstrate lower skull stiffness and higher stress in the orbital region of the former when biting with carnassial teeth, suggesting that Chinese Crocuta could not process prey with the same degree of efficiency as extant Crocuta crocuta. Dental microwear texture data further support this interpretation, as Chinese Crocuta have intermediate and indistinguishable complexity values (indicative of hard-object feeding) between the extant African lion (Panthera leo) and extant hyenas (C. crocuta, Hyaena hyaena, and Parahyaena brunnea), being most similar to the omnivorous P. brunnea. The use of dental macrowear to infer dietary behavior may also be possible in extinct taxa, as evinced by dietary correlations between extant African feliforms and dental macrowear assignments. Collectively, this multiproxy analysis suggests that Chinese Crocuta may have exhibited dietary behavior distinct from that of living C. crocuta, and assumptions of niche conservatism may mask significant dietary variation in species broadly distributed in time and space.

Isotaphonomy in concept and practice: an exploration of vertebrate microfossil bonebeds in the Upper Cretaceous (Campanian) Judith River Formation, north-central Montana

Abstract: Vertebrate microfossil bonebeds (VMBs)—localized concentrations of small resilient vertebrate hard parts—are commonly studied to recover otherwise rarely found small-bodied taxa, and to document relative taxonomic abundance and species richness in ancient vertebrate communities. Analyses of taphonomic comparability among VMBs have often found significant differences in size and shape distributions, and thus considered them to be non-isotaphonomic. Such outcomes of “strict” statistical tests of isotaphonomy suggest discouraging limits on the potential for broad, comparative paleoecological reconstruction using VMBs. Yet it is not surprising that sensitive statistical tests highlight variations among VMB sites, especially given the general lack of clarity with regard to the definition of “strict” isotaphonomic comparability. We rigorously sampled and compared six VMB localities representing two distinct paleoenvironments (channel and pond/lake) of the Upper Cretaceous Judith River Formation to evaluate biases related to sampling strategies and depositional context. Few defining distinctions in bioclast size and shape are evident in surface collections, and most site-to-site comparisons of sieved collections are indistinguishable (p≤ 0.003). These results provide a strong case for taphonomic equivalence among the majority of Judith River VMBs, and bode well for future studies of paleoecology, particularly in relation to investigations of faunal membership and community structure in Late Cretaceous wetland ecosystems. The taphonomic comparability of pond/lake and channel-hosted VMBs in the Judith River Formation is also consistent with a formative model that contends that channel-hosted VMBs were reworked from pre-existing pond/lake assemblages, and thus share taphonomic history.

Extrapolating body masses in large terrestrial vertebrates

Abstract: Despite more than a century of interest, body-mass estimation in the fossil record remains contentious, particularly when estimating the body mass of taxa outside the size scope of living animals. One estimation approach uses humeral and femoral (stylopodial) circumferences collected from extant (living) terrestrial vertebrates to infer the body masses of extinct tetrapods through scaling models. When applied to very large extinct taxa, extant-based scaling approaches incur obvious methodological extrapolations leading some to suggest that they may overestimate the body masses of large terrestrial vertebrates. Here, I test the implicit assumption of such assertions: that a quadratic model provides a better fit to the combined humeral and femoral circumferences-to-body mass relationship. I then examine the extrapolation potential of these models through a series of subsetting exercises in which lower body-mass sets are used to estimate larger sets. Model fitting recovered greater support for the original linear model, and a nonsignificant second-degree term indicates that the quadratic relationship is statistically linear. Nevertheless, some statistical support was obtained for the quadratic model, and application of the quadratic model to a series of dinosaurs provides lower mass estimates at larger sizes that are more consistent with recent estimates using a minimum convex-hull (MCH) approach. Given this consistency, a quadratic model may be preferred at this time. Still, caution is advised; extrapolations of quadratic functions are unpredictable compared with linear functions. Further research testing the MCH approach (e.g., the use of a universal upscaling factor) may shed light on the linear versus quadratic nature of the relationship between the combined femoral and humeral circumferences and body mass.

High-latitude settings promote extreme longevity in fossil marine bivalves

Abstract: One of the longest-lived, noncolonial animals on the planet today is a bivalve that attains life spans in excess of 500 years and lives in a cold, seasonally food-limited setting. Separating the influence of temperature and food availability on life span in modern settings is difficult, as these two conditions covary. The life spans of fossil animals can provide insights into the role of environment in the evolution of extreme longevity that are not available from studies of modern taxa. We examine bivalves from the unique, nonanalogue, warm and high-latitude setting of Seymour Island, Antarctica, during the greenhouse intervals of the Late Cretaceous and Paleogene. Despite significant sampling limitations, we find that all 11 species examined are both slow growing and long-lived, especially when compared with modern bivalves living in similar temperature settings. While cool temperatures have long been thought to be a key factor in promoting longevity, our findings suggest an important role for caloric restriction brought about by the low and seasonal light regime of the high latitudes. Our life-history data, spanning three different families, emphasize that longevity is in part governed by environmental rather than solely phylogenetic or ecologic factors. Such findings have implications for both modern and ancient latitudinal diversity gradients, as a common correlate of slow growth and long life is delayed reproduction, which limits the potential for evolutionary change. While life spans of modern bivalves are well studied, data on life spans of fossil bivalves are sparse and largely anecdotal. Life histories of organisms from deep time can not only elucidate the controls on life span but also add a new dimension to our understanding of macroevolutionary patterns.

Can secondary osteons be used as ontogenetic indicators in sauropods? Extending the histological ontogenetic stages into senescence

Abstract: Sauropod bone histology has provided a great deal of insight into the life history of these enormous animals. However, because of high growth rates, annual growth rings are not common in sauropod long bones, so directly measuring growth rates and determining sexual maturity require alternative measures. Histological ontogenetic stages (HOS) have been established to describe the changes in bone histology through development for basal Macronaria and Diplodocoidea, and subsequently for Titanosauria. Despite this, the current HOS model is not able to discriminate bone tissues in late ontogeny, when sauropods had reached asymptotic size and continued to live into senescence but their long bones became extensively remodeled by secondary osteons and all primary bone was destroyed. Here we establish remodeling stages (RS) to characterize the Haversian bone development through ontogeny in eight sauropod taxa (Apatosaurinae, Giraffatitan brancai, Camarasaurus spp., Dicraeosaurus spp., Ampelosaurus atacis, Phuwiangosaurus sirindhornae, Magyarosaurus dacus, and Alamosaurus sanjuanensis) and find significant correlation of RS with corresponding femur length (CFL) for the studied taxa, with the exception of Dicraeosaurus and Magyarosaurus. Remodeling stages are based on the maximum number of observable generations of crosscutting osteons from the innermost, mid-, and outermost part of the cortex. The correlation with CFL indicates that secondary osteons present an ontogenetic signal that could extend the histological ontogenetic stages. Remodeling stages also provide additional insight into the changes in histology through ontogeny for Sauropoda. This method has the potential to be used in other taxa, such as thyreophorans and many ornithischians, that develop Haversian tissue through development.

Asymmetric geographic range expansion explains the latitudinal diversity gradients of four major taxa of marine plankton

Abstract: . Extensive investigation of the close association between biological diversity and environmental temperature has not yet yielded a generally accepted, empirically validated mechanism to explain latitudinal gradients of species diversity, which occur in most taxa. Using the highly resolved late Cenozoic fossil records of four major taxa of marine plankton, we show that their gradients arise as a consequence of asymmetric geographic range expansion rather than latitudinal variation in diversification rate, as commonly believed. Neither per capita speciation nor extinction rates trend significantly with temperature or latitude for these marine plankton. Species of planktonic foraminifera and calcareous nannoplankton that originate in the temperate zone preferentially spread toward and arrive earlier in the tropics to produce a normal gradient with tropical diversity peaks; by contrast, temperate-zone originating species of diatoms and radiolarians preferentially spread toward and arrive earlier in p...

Temporal dynamics of encrusting communities during the Late Devonian: a case study from the Central Devonian Field, Russia

Abstract: In this study we focused on the dynamics of encrusting assemblages preserved on brachiopod hosts collected from upper Frasnian and lower Famennian deposits of the Central Devonian Field, Russia Because the encrusted brachiopods come from deposits bracketing the Frasnian/Famennian (F/F) boundary, the results also shed some light on ecological differences in encrusting communities before and after the Frasnian—Famennian (F-F) event To explore the diversity dynamics of encrusting assemblages, we analyzed more than 1300 brachiopod valves (substrates) from two localities Taxon accumulation plots and shareholder quorumsubsampling (SQS) routines indicated that a reasonably small sample of brachiopod host valves (n=50) is sufficient to capture themajority of the encrusting genera recorded at a given site The richness of encrusters per substrate declined simultaneously with the number of encrusting taxa in the lower Famennian, accompanied by a decrease in epibiont abundance, with a comparable decrease in mean encrustation intensity (percentage of bioclasts encrusted by one or more epibionts) Epibiont abundance and occupancy roughlymirror each other Strikingly, few ecological characteristics are correlated with substrate size, possibly reflecting random settlement of larvae Evenness, which is negatively correlated with substrate size, shows greater within-stage variability among samples than between Frasnian and Famennian intervals and may indicate the instability of early Famennian biocenoses following the faunal turnover The occurrence distribution of encrusters points to nonrandomassociations and exclusions among several encrusting taxa However, abundance and occupancy of microconchids remained relatively stable throughout the sampled time interval The notable decline in abundance (∼60%) and relatively minor decline in diversity (∼30%) suggest jointly that encrusting communities experienced ecological collapse rather than a major mass extinction event The differences between the upper Frasnian and lower Famennian encrusting assemblages may thus record a turnover associated with the F-F event

Can latitudinal richness gradients be measured in the terrestrial fossil record

Abstract: Studying the deep-time origins of macroecological phenomena can help us to understand their long-term drivers. Given the considerable spatiotemporal bias of the terrestrial fossil record, it behooves us to understand how much biological information is lost. The aim of this study is to establish whether latitudinal diversity gradients are detectable in a biased terrestrial fossil record. I develop a simulated fossilization approach, weighting the probability of terrestrial mammal species appearing in the fossil record based on body size and geographic-range size; larger species with larger range sizes are more likely to enter the fossil record. I create simulated fossil localities from the modern North American mammal record. I vary the percentage of species successfully fossilized and estimate the magnitude of the latitudinal diversity gradient (slope of the richness gradient and degree of species turnover). I find that estimates of the latitudinal diversity gradient are sensitive to the loss of species with small body size and geographic-range sizes. In some cases, simulated fossil-record bias completely obliterates evidence of declining richness with latitude, a phenomenon that is not ameliorated by the application of nonparametric richness estimation. However, if the rate of preservation is medium (50% of species) to high (75% of species), the magnitude of the latitudinal diversity gradient can be reliably estimated. Similarly, changes in the diversity gradient estimates are largely explained by differences in the diversity–climate relationship among iterations, suggesting that these relationships may be measurable in the fossil record.

Does my posterior look big in this? The effect of photographic distortion on morphometric analyses

Abstract: Most geometric morphometric studies are underpinned by sets of photographs of specimens. The camera lens distorts the images it takes, and the extent of the distortion will depend on factors such as the make and model of the lens and camera and user-controlled variation such as the zoom of the lens. Any study that uses populations of geometric data digitized from photographs will have shape variation introduced into the data set simply by the photographic process. We illustrate the nature and magnitude of this error using a 30-specimen data set of Recent New Zealand Mactridae (Mollusca: Bivalvia), using only a single camera and camera lens with four different photographic setups. We then illustrate the use of retrodeformation in Adobe Photoshop and test the magnitude of the variation in the data set using multivariate Procrustes analysis of variance. The effect of photographic method on the variance in the data set is significant, systematic, and predictable and, if not accounted for, could lead to misleading results, suggest clustering of specimens in ordinations that has no biological basis, or induce artificial oversplitting of taxa. Recommendations to minimize and quantify distortion include: (1) that studies avoid mixing data sets from different cameras, lenses, or photographic setups; (2) that studies avoid placing specimens or scale bars near the edges of the photographs; (3) that the same camera settings are maintained (as much as practical) for every image in a data set; (4) that care is taken when using full-frame cameras; and (5) that a reference grid is used to correct for or quantify distortion.

Evolutionarily distinct “living fossils” require both lower speciation and lower extinction rates

Abstract: As a label for a distinct category of life, “living fossil” is controversial. The term has multiple definitions, and it is unclear whether the label can be genuinely used to delimit biodiversity. Even taking a purely phylogenetic perspective in which a proxy for the living fossil is evolutionary distinctness (ED), an inconsistency arises: Does it refer to “dead-end” lineages doomed to extinction or “panchronic” lineages that survive through multiple epochs? Recent tree-growth model studies indicate that speciation rates must have been unequally distributed among species in the past to produce the shape of the tree of life. Although an uneven distribution of speciation rates may create the possibility for a distinct group of living fossil lineages, such a grouping could only be considered genuine if extinction rates also show a consistent pattern, be it indicative of dead-end or panchronic lineages. To determine whether extinction rates also show an unequal distribution, we developed a tree-growth model in which the probability of speciation and extinction is a function of a tip’s ED. We simulated thousands of trees in which the ED function for a tip is randomly and independently determined for speciation and extinction rates. We find that simulations in which the most evolutionarily distinct tips have lower rates of speciation and extinction produce phylogenetic trees closest in shape to empirical trees. This implies that a distinct set of lineages with reduced rates of diversification, indicative of a panchronic definition, is required to create the shape of the tree of life.

Grasping the shape of belemnoid arm hooks : a quantitative approach

Abstract: Chitinous arm hooks (onychites) of belemnoid coleoid cephalopods are widely distributed in Mesozoic sediments. Due to their relative abundance and variable morphology compared with the single, bullet-shaped, belemnite rostrum, arm hooks came into the focus of micropaleontologists as a promising index fossil group for the Jurassic–Cretaceous rock record and have been the target of functional, ecological, and phylogenetic interpretations in the past. Based on three well-preserved arm crowns of the Toarcian diplobelid Chondroteuthis wunnenbergi, we analyzed the shape of a total of 87 micro-hooks. The arm crown of Chondroteuthis is unique in having uniserial rather than biserial hooks. The first application of elliptic Fourier shape analysis to the arm weapons of belemnoid coleoids allows for the distinction of four micro-hook morphotypes and the quantification of shape variation within these morphotypes. Based on the best-preserved arm crown, we reconstructed the distribution of morphotypes within the arm crown and along a single arm. Our quantitative data support former observations that smaller hooks were found close to the mouth and at the most distal arm parts, while the largest hooks were found in the central part of the arm crown. Furthermore, we found a distinct arm differentiation, as not every arm was equipped with the same hook morphotype. Here, we report the functional specialization of the belemnoid arm crown for the first time and speculate about the potential function of the four morphotypes based on comparisons with modern cephalopods. Our analyses suggest a highly adapted functional morphology and intra-individual distribution of belemnoid hooks serving distinct purposes mainly during prey capture.

Predation on feather stars by regular echinoids as evidenced by laboratory and field observations and its paleobiological implications

Abstract: Among extant crinoids, the feather stars are the most diverse and occupy the greatest bathymetric range, being especially common in reef environments. Feather stars possess a variety of morphological, behavioral and physiological traits that have been hypothesized to be critical to their success, especially in their ability to cope with predation. However, knowledge of their predators is exceptionally scant, consisting primarily of circumstantial evidence of attacks by fishes. In this study the question whether regular echinoids, recently shown to consume stalked crinoids, also consume feather stars is explored. Aquarium observations indicate that regular echinoids find feather stars palatable, including feather stars known to be distasteful to fish, and that regular echinoids can capture and eat live feather stars, including those known to swim. Gut-content analyses of the echinoid Araeosoma fenestratum (Thomson, 1872), which is commonly observed with large populations of the feather star Koehlermetra porrecta (Carpenter, 1888) in video transects from marine canyons off the coast of France, revealed elements of feather stars in the guts of 6 of 13 individuals. The high proportion of crinoid material (up to 90%), and the presence of articulated crinoid skeletal elements in the gut of A. fenestratum , suggest that these echinoids consumed at least some live crinoids, although they may have also ingested some postmortem remains found in the sediment. Additionally, photographic evidence from the northeast Atlantic suggests that another regular echinoid, Cidaris cidaris (Linnaeus, 1758), preys on feather stars. Thus in spite of the broad suite of antipredatory adaptations, feather stars are today subject to predation by regular echinoids and may have been since the Mesozoic, when this group of crinoids first appeared.

Sexual dimorphism and sexual selection in cytheroidean ostracodes from the Late Cretaceous of the U.S. Coastal Plain

Abstract: Sexual dimorphism is common in many extant animals, but it is difficult to demonstrate in fossil species. Working with material from the Late Cretaceous of the U.S. Coastal Plain, we herein analyze sexual dimorphism in ostracodes from the superfamily Cytheroidea, a group whose extant members have males that are relatively more elongate than females. We digitized outlines of more than 6000 individual ostracode valves or carapaces, extracted size (area) and shape (length-to-height ratio) information, and used finite mixture models to assess hypotheses of sexual dimorphism. Male and female clusters can be discerned in nearly all populations with sufficient data, resulting in estimates of size and shape dimorphismfor 142 populations across 106 species; an additional nine samples are interpreted to consist only of females. Dimorphism patterns varied across taxa, especially for body size: males range from 30% larger to 20% smaller than females. Magnitudes of sexual dimorphism are generally stable within species across time and space; we can demonstrate substantial evolutionary changes in dimorphism in only one species, Haplocytheridea renfroensis. Several lines of evidence indicate that patterns of sexual dimorphism in these ostracodes reflect male investment in reproduction, suggesting that this study system has the potential to capture variation in sexual selection through the fossil record.

Chronologie du site moustérien de type Quina des Pradelles (Marillac-le-Franc, Charente, France)

Abstract: Cet article presente une synthese des donnees chronologiques du site des Pradelles (Marillac-le-Franc, Charente, France). Le gisement se caracterise dans son locus est par un remplissage de pres de quatre metres d’epaisseur ayant livre des depots de la fin du Paleolithique moyen dans lesquels une industrie mousterienne de type Quina est associee a une faune abondante largement dominee par le renne. Durant les fouilles conduites par B. Maureille et A. Mann entre 2001 et 2013, les donnees chronologiques obtenues pour ce locus ont ete peu nombreuses : une datation par thermoluminescence (TL) sur un silex chauffe et une autre par U-Th sur un speleotheme situe dans la partie inferieure de la sequence. Des analyses par le radiocarbone ont ete egalement realisees sur des ossements provenant du sommet du remplissage, mais se sont revelees partiellement infructueuses en raison de l’anciennete des vestiges proche de la limite de la methode.

Prehistory of human tuberculosis: Earliest evidence from the onset of animal husbandry in the Near East

Abstract: La tuberculose a ete consideree, pendant longtemps, comme une zoonose transmise a l’homme par des bovins, notamment lors du processus de domestication de l’aurochs au Neolithique. Des travaux de phylogenie moleculaire recents ont remis en question ce dogme, montrant que le complexe Mycobacterium tuberculosis (MTBC) a existe comme pathogene humain depuis environ trois millions d’annees. Cependant, des etudes recentes basees sur deux horloges moleculaires differentes ont propose que la tuberculose humaine date de moins de 6 000 ans. Afin d’apporter de nouvelles donnees a ce debat, nous avons etudie les marqueurs paleopathologiques de la tuberculose sur des restes humains decouverts dans le berceau proche-oriental de la Neolithisation, sur les sites de Dja’de el-Mughara (9310-8290 cal. BC) dans la moyenne Vallee de l’Euphrate (Syrie du Nord) et de Tell Aswad (8200-7500 cal. BC) au Levant central (Syrie du Sud). Ces deux sites ont livre chacun les restes squelettiques de plus d’une centaine d’individus qui ont fait l’objet de pratiques funeraires diverses. Les resultats obtenus par differentes approches (paleopathologie, micro-tomodensitometrie, paleomicrobiologie) confirment que ces vestiges constituent les plus anciens cas de la tuberculose humaine (un adulte et neuf immatures a Dja’de el-Mughara et un adulte a Tell Aswad) precedant et accompagnant l’emergence de la domestication des bovins au Proche-Orient. Parmi les onze cas identifies, cinq individus ont ete enterres dans la Maison des Morts a Dja’de el-Mughara, les autres etaient inhumes dans des sepultures primaires, plurielles et mixtes. Sur la base de ces resultats, le futur defi serait de comprendre le role du contact etroit entre les humains et les animaux dans l’evolution du MTBC et les mecanismes d’emergence et de diffusion des souches modernes de la tuberculose humaine. Dans cette perspective, le Levant apparait comme une region cle pendant les premieres phases de la domestication animale et de la sedentarisation.

An unknown phanerozoic driver of brachiopod extinction rates unveiled by multivariate linear stochastic differential equations

Abstract: Whether the evolutionary dynamics of one group of organisms influence that of another group of organisms over the vast timescale of the geological record is a difficult question to tackle. This is not least because multiple factors can influence or mask the effects of potential driving forces on evolutionary dynamics of the focal group. Here, we show how an approach amenable to causality inference for time series, linear stochastic differential equations (SDEs), can be used in a multivariate fashion to shed light on driving forces of diversification dynamics across the Phanerozoic. Using a new, enhanced stepwise search algorithm, we searched through hundreds of models to converge on a model that best describes the dynamic relationships that drove brachiopod and bivalve diversification rates. Using this multivariate framework, we characterized a slow process (half-life of c. 42 Myr) that drove brachiopod extinction. This slow process has yet to be identified from the geological record. Using our new framework for analyzing multiple linear SDEs, we also corroborate our previous findings that bivalve extinction drove brachiopod origination in the sense that brachiopods tended to diversify at a greater rate when bivalves were removed from the system. It is also very likely that bivalves “self-regulate” in the sense that bivalve extinctions also paved the way for higher bivalve origination rates. Multivariate linear SDEs as we presented them here are likely useful for studying other dynamic systems whose signatures are preserved in the paleontological record.

Evaluating the accuracy of biodiversity changes through geologic times: from simulation to solution

Abstract: Estimating biodiversity and its variations through geologic time is a notoriously difficult task, due to several taphonomic and methodological effects that make the reconstructed signal potentially distinct from the unknown, original one. Through a simulation approach, we examine the effect of a major, surprisingly still understudied, source of potential disturbance: the effect of time discretization through biochronological construction, which generates spurious coexistences of taxa within discrete time intervals (i.e., biozones), and thus potentially makes continuous- and discrete-time biodiversity curves very different. Focusing on the taxonomic-richness dimension of biodiversity (including estimates of origination and extinction rates), our approach relies on generation of random continuous-time richness curves, which are then time-discretized to estimate the noise generated by this manipulation. A broad spectrum of data-set parameters (including average taxon longevity and biozone duration, total number of taxa, and simulated time interval) is evaluated through sensitivity analysis. We show that the deteriorating effect of time discretization on the richness signal depends highly on such parameters, most particularly on average biozone duration and taxonomic longevity because of their direct relationship with the number of false coexistences generated by time discretization. With several worst-case but realistic parameter combinations (e.g., when relatively short-lived taxa are analyzed in a long-ranging biozone framework), the original and time-discretized richness curves can ultimately show a very weak to zero correlation, making these two time series independent. Based on these simulation results, we propose a simple algorithm allowing the back-transformation of a discrete-time taxonomic-richness data set, as customarily constructed by paleontologists, into a continuous-time data set. We show that the reconstructed richness curve obtained this way fits the original signal much more closely, even when the parameter combination of the original data set is particularly adverse to an effective time-discretized reconstruction.

The same picture through different lenses: quantifying the effects of two preservation pathways on Green River Formation insects

Abstract: . Insects in the fossil record are generally preserved in lacustrine shales or in amber. For those in lacustrine shales, preservation is usually via keroginization or mineralization. Given the extended period of microbial decay required to generate ions for mineralization, there is a predicted inherent bias toward lower preservation quality for this pathway by most taphonomic indices compared with keroginization. This study tests this hypothesis by comparing multiple measures of preservation quality between sites with similar sedimentology in the Eocene Green River Formation of Colorado. Here, insects are either mineralized in iron oxides (likely after pyrite) at the Paleoburn site or keroginized at the Anvil Points site. Generally, the prediction that keroginization preserves soft-bodied fossils with higher preservational quality than mineralization is affirmed, but with some caveats. Beetles, known for their robust cuticles, are proportionately more abundant at the Paleoburn site, but eight of t...

Tooth occlusal morphology in the durophagous marine reptiles, Placodontia (Reptilia: Sauropterygia)

Abstract: Placodontia were a group of marine reptiles that lived in shallow nearshore environments during the Triassic. Based on tooth morphology it has been inferred that they were durophagous, but tooth morphology differs among species: placodontoid placodonts have teeth described as hemispherical, and the teeth of more highly nested taxa within the cyamodontoid placodonts have been described as flat. In contrast, the sister taxon to the placodonts, Palatodonta bleekeri, like many other marine reptiles, has tall pointed teeth for eating soft-bodied prey. The goals of this paper are to quantify these different tooth morphologies and compare tooth shape among taxa and with a functionally “optimal” tooth. To quantify tooth morphology we measured the radius of curvature (RoC) of the occlusal surface by fitting spheres to 3D surface scans or computed microtomographic scans. Large RoCs correspond to flatter teeth, while teeth with smaller RoCs are pointier; positive RoCs have convex occlusal surfaces, and a negative RoC indicates that the occlusal surface of the tooth is concave. We found the placodontoid taxa have teeth with smaller RoCs than more highly nested taxa, and palatine teeth tend to be flatter and closer to the optimal morphology than maxillary teeth. Within one well-nested clade, the placochelyids, the rearmost palatine teeth have a more complex morphology than the predicted optimal tooth, with an overall concave occlusal surface with a small, medial cusp. These findings are in keeping with the hypothesis that placodonts were specialized durophagous predators with teeth modified to break hard prey items while resisting tooth failure.

An alternative date for the Nahal Mitnan Cairn Field in the Western Negev Highlands: Identifying an Early Timnian tumuli tradition in the Southern Levant

Abstract: M. Haiman, Service des Antiquites d’Israel, a identifie des centaines de tumuli sur le plateau du Neguev occidental, Israel. Les prospections et fouilles qu’il a menees a Nahal Mitnan sur un champ de tumuli lui ont fourni des donnees pour identifier des occupations de l’âge du Bronze ancien au sein de ces tumuli. Il les a dates, et d’autres de meme forme sur le plateau du Neguev, de l’âge du Bronze ancien ou du Bronze ancien II. Je soutiens que l’architecture et la culture materielle du Bronze ancien sont intrusives et n’ont aucun rapport avec la construction d’origine et la fonction du champ de tumuli de Nahal Mitnan. Mon argumentation est tiree des releves d’architecture detailles realises par Haiman, qui contribuent a dater la construction de tumuli specifiques et des structures qui leur sont associees. A l’appui des donnees d’Al-Thulaythuwat en Jordanie et de Ramat Saharonim dans le Neguev central, le champ de tumuli de Nahal Mitnan peut etre date soit du Neolithique recent, soit du Neolithique recent/ Chalcolithique. Ces tumuli sont egalement presents dans l’ensemble des zones arides du Levant Sud ; mais les dimensions de la chambre funeraire varient suivant les regions, ce qui indique qu’il existe des differences dans les pratiques funeraires. Je considere que les tumuli de Nahal Mitnan n’etaient pas le lieu de repos ultime pour le defunt, mais qu’ils representaient une etape dans un processus funeraire encore inconnu. Enfin, ce champ de tumuli est interprete comme faisant partie d’un complexe funeraire plus vaste du Timnien ancien, qui s’etendait du sud du Sinai au plateau du Neguev occidental.