SEARCH · Search bioRxiv

Results for “Paleontology”

Search indexed bioRxiv preprints in genomics, neuroscience, cell biology and bioinformatics. Read source abstracts and check manuscript versions; preprints are not peer reviewed.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

63 records · Page 4Linked to original sources

bioRxiv2018

New cheloniellid arthropod with large raptorial appendages from the Silurian of Wisconsin, USA

Cheloniellids comprise a small, distinctive group of Paleozoic arthropods of whose phylogenetic relationships within the Arthropoda remain unresolved. A new form, Xus yus, n. gen, n. sp. is reported from the Waukesha Lagerstatte in the Brandon Bridge Formation (Silurian: Telychian), near Waukesha, Wisconsin, USA. Exceptionally preserved specimens show previously poorly known features including biramous appendages; this is the first cheloniellid to show large, anterior raptorial appendages. We emend the diagnosis of Cheloniellida; cephalic appendages are uniramous and may include raptorial appendages; trunk appendages are biramous.

paleontology↗

bioRxiv2018

Reversing Time Averaging and Reconstructing Extinction Rates with Approaches from Image Processing

In this paper, the relation between the extinction rate and the rate of last fossil occurrences as well as the relation between the fossil occurrence rate and the time averaged fossil occurrence rate is examined. Both relations are described by the same mathematical operation. This operation is commonly used in image processing, where it generates a blurring effect. Therefore the rate of last fossil occurrences can be taken as a blurred version of the extinction rate, and the time averaged fossil occurrence rate as a blurred version of the fossil occurrence rate. This connection has different applications. It allows to study the patterns different types of time averaging generate or the patterns of last fossil occurrences generated by different extinction rates. More importantly, it opens the possibility to use algorithms from image processing that reverse blurring effects for geological applications. This can be used to reverse the effects of time averaging or to reconstruct extinction rates from the rate of last fossil occurrences.

paleontology↗

bioRxiv2018

Surface sediment samples from early age of seafloor exploration can provide a late 19th century baseline of the marine environment

Ocean-floor sediment samples collected up to 150 years ago represent an important historical archive to benchmark global changes in the seafloor environment, such as species range shifts and invasions and pollution trends. Such benchmarking requires that the historical sediment samples represent the state of the environment at or shortly before the time of collection. However, early oceanographic expeditions sampled the ocean floor using devices like the sounding tube or a dredge, which potentially disturb the sediment surface and recover a mix of Holocene (surface) and deeper, Pleistocene sediments. Here we use climate-sensitive microfossils as a fast biometric method to assess if historical seafloor samples contain a mixture of modern and glacial sediments. Our assessment is based on comparing the composition of planktonic foraminifera (PF) assemblages in historical samples with Holocene and Last Glacial Maximum (LGM) global reference datasets. We show that eight out of the nine historical samples contain PF assemblages more similar to the Holocene than to the LGM PF assemblages, but the comparisons are only significant when there is a high local species temporal turnover (from the LGM to the Holocene). When analysing temporal turnover globally, we show that upwelling and temperate regions had greatest species turnover, which are areas where our methodology would be most diagnostic. Our results suggest that sediment samples from historical collections can provide a baseline of the state of marine ecosystems in the late 19th century, and thus be used to assess ocean global change trends.

paleontology↗

bioRxiv2018

The R package divDyn for quantifying diversity dynamics using fossil sampling data

O_LIUnbiased time series of diversity dynamics are vital for quantifying the grand history of life. Applications include identifying ancient mass extinctions and inferring both biotic and abiotic controls on diversification rates.\nC_LIO_LIWe introduce divDyn, a new R package that facilitates the calculation of taxonomic richness, extinction and origination rates from time-binned fossil sampling data. State-of-the-art sampling completeness metrics, counting protocols, and sampling standardisation functions permit the reconstruction of biologically meaningful time series. Additional functions permit the partitioning of turnover rates by trait and environmental affinity.\nC_LIO_LIWe display Phanerozoic-scale diversity dynamics of marine invertebrates using the divDyn package. Using the core function and standard subsampling options, we revisit earlier assessments of declining extinction and origination rates over time and of equilibrial diversity dynamics to assess their methodological dependency.\nC_LIO_LIThe modular and fast implementation of published methods ensures traceability, reproducibility, and comparability of future studies.\nC_LI

paleontology↗

bioRxiv2018

Illustrating phylogenetic placement of fossils using RoguePlots: An example from ichneumonid parasitoid wasps (Hymenoptera, Ichneumonidae) and an extensive morphological matrix

The fossil record constitutes the primary source of information about the evolutionary history of extant and extinct groups, and many analyses of macroevolution rely on fossils that are accurately placed within phylogenies. To avoid misinterpretation of the fossil record, especially by non-palaeontologists, the proper assessment and communication of uncertainty in fossil placement is crucial. We here use Bayesian morphological phylogenetics to evaluate the classifications of fossil parasitoid wasps (Hymenoptera, Ichneumonidae) and introduce RoguePlots to illustrate placement uncertainty on the phylogeny of extant taxa. Based on an extensive, newly constructed morphological matrix of 222 characters in 24 fossil and 103 extant taxa, we test three different aspects of models of morphological evolution. We find that a model that includes ordered characters, among-character rate variation, and a state-space restricted to observed states achieves the highest marginal likelihoods. The individual RoguePlots reveal large differences in confidence in the placement of the different fossils and allow some refinements to their classification: Polyhelictes bipolarus and Ichninsum appendicrassum are moved from an uncertain subfamily placement to Pimplinae, Plectiscidea lanhami is transferred to Allomacrus in Cylloceriinae (Allomacrus lanhami, comb. nov.), Lithotorus cressoni is moved from Diplazontinae to Orthocentrinae, and we note uncertainty in the generic placement of Xanthopimpla? messelensis. We discuss potential artefacts that might result in biased posterior probabilities in Bayesian morphological phylogenetic analyses, pertaining to character and taxon sampling, fossilization biases, and model misspecification. Finally, we suggest future directions both in ichneumonid palaeontology, in the modelling of morphological evolution, and in the way Bayesian phylogenetics can improve both assessment and representation of fossil placement uncertainty.

paleontology↗

bioRxiv2018

The ecomorphology of southern African rodent incisors: Potential applications to the hominin fossil record

The taxonomic identification of mammalian fauna within fossil assemblages is a well-established component of paleoenvironmental reconstructions. However, many fragmentary specimens recovered from fossil sites are often disregarded as they can be difficult to identify with the precision required for taxonomic methods. For this reason, the large numbers of isolated rodent incisors that are often recovered from hominin fossil bearing sites have generally been seen as offering little interpretive value. Ecomorphological analysis, often referred to as a \"taxon-free\" method, can potentially circumvent this problem by focusing on the adaptive, rather than the taxonomic significance of rodent incisor morphology. Here, we determine if the morphology of the upper incisors of modern southern African rodents reflects dietary behavior using discriminant function analysis. Our model suggests that a strong ecomorphological signal exists in our modern sample and we apply these results to two samples of isolated incisors from the hominin fossil bearing sites, Sterkfontein and Swartkrans.

paleontology↗

bioRxiv2018

Absence of general rules governing molluscan body-size response to climatic fluctuation during Cenozoic

Body size is a key factor in dictating the fate of interaction between an organism and its surrounding environment. A negative temperature-size relationship (TSR) has been suggested as one of the universal responses to climatic warming. It is also predicted that groups with narrow latitudinal range, tropical affinity and higher body size, would show higher sensitivity to climatic fluctuation. Moreover, because of the difference in thermal sensitivity, it is also expected that the response to climatic fluctuation would be different between epifaunal and infaunal groups. To confirm the generality of these relationship among marine families, we compiled the relationship between body-size and global temperature trends over Cenozoic using a database of marine benthic molluscs of class gastropoda and bivalvia resolved to temporal stages. We evaluated the dependence of climate induced body-size response to the existing size and latitudinal spread via correlating the first-difference correlation coefficient of temperature-size ({rho}1st (size-temp)) with maximum size and latitudinal spread of family respectively. Cenozoic record of this highly diverse group does not show any signature of TSR for molluscan class or for any other regional, ecological groups during the past 66My long climatic fluctuation. We did not find any evidence supporting heightened response to climatic fluctuation in groups with limited latitudinal spread or with large body-size. The tropical species did not show significant difference in their body-size response in comparison to temperate species. It also shows lack of any difference in response between ecological groups of molluscs with varying substrate relationship and hence, refutes the predicted variation due to difference in thermal specialization. Although a negative correlation between maximum latitudinal spread and {rho}1st (size-temp) is observed for infaunal families, it is not statistically significant. Our results highlight the limited validity of \"universal rules\" in explaining the climate induced morphological response of marine communities in deep time and underscores the complexity in generalizing the biotic outcome of future climatic fluctuation.

paleontology↗

bioRxiv2018

A new method for enamel amino acid racemization dating: a closed system approach

Analysis of the predictable breakdown of proteins and amino acids in ancient biominerals enables age estimation over the Quaternary. We postulate that enamel is a suitable biomineral for the long-term survival of endogenous amino acids. Analysis of multiple amino acids for geochronological studies is typically achieved using a RP-HPLC method. However, the low concentrations of amino acids coupled with high concentrations of inorganic species make accurate determination of amino concentrations challenging. We have developed a method for the routine preparation of multiple enamel samples using biphasic separation. Furthermore, we have shown that amino acids that exhibit effectively closed system behaviour can be isolated from enamel through an exposure time of 72 h to bleach. Elevated temperature experiments investigating the processes of intra-crystalline protein degradation (IcPD) do not appear to match the patterns from fossil samples, reinforcing the need for a comprehensive understanding of the underlying mechanisms of protein degradation. This novel preparative method isolates intra-crystalline amino acids suitable for the development of mammalian geochronologies based on enamel protein degradation. The lower rates of racemisation in enamel (cf. Bithynia opercula) suggest that the enamel AAR may be able to be used as a relative dating technique over time scales > 2.8 Ma. Enamel AAR has the potential to estimate the age of mammalian remains past the limit of all other current direct dating methods, providing an invaluable tool for geochronological studies.

paleontology↗

bioRxiv2026

Constraining Palaeogeography and Palaeotides for the Cambrian using cnidarian medusae

The ocean tides influence key Earth system processes at a range of spatial and temporal scales. It is known that the geometry of ocean basins is the leading controller of tidal energetics, so well-constrained palaeogeographic reconstructions and tidal properties for Earths past are imperative when investigating other Earth system processes. Here, we present a novel way to constrain both deep-time tidal model results and reconstructions, by combining palaeoecology with sedimentology. We compare new palaeo-tidal model simulations for the Cambrian period, significant for the early origin and radiation of major animal fauna, to tidal proxies. One of the most abundant soft-bodied organisms preserved during this time are cnidarian medusae (jellyfish). A total of 17 cnidarian medusae localities were obtained through the literature, which had an adequate global distribution and occurred at regular intervals throughout the period of study. In some locations there were also estimates of palaeo-tidal range. Our results show a good agreement between the simulations and proxy data. In the few locations where there is disagreement, it is proposed that the palaeogeographic reconstructions are missing details, e.g., island chains, and our results allow for the palaeogeographic reconstructions to be improved. The proxy method presented is promising and can be applied to other time-periods with different marine fossils, particularly at evolutionary and extinction periods where the marginal marine environment is of importance.

paleontology↗