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 Read source abstracts and check manuscript versions; preprints are not peer reviewed.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.

At least 271 records · Page 15Linked to original sources

bioRxiv2022

Femora from an exceptionally large population of coeval ornithomimosaurs yield evidence of sexual dimorphism in extinct theropod dinosaurs

Sexual dimorphism is challenging to detect among fossils, due to a lack of statistical representativeness. The Angeac-Charente Lagerstatte (France) represents a remarkable "snapshot" from a Berriasian (Early Cretaceous) ecosystem and offers a unique opportunity to study intraspecific variation among a herd of at least 61 coeval ornithomimosaurs. Herein, we investigated the hindlimb variation across the best-preserved specimens from the herd through 3D Geometric Morphometrics and Gaussian Mixture Modelling. Our results based on complete and fragmented femora evidenced a dimorphism characterized by variations in the shaft curvature and the distal epiphysis width. Since the same features vary between sexes among modern avian dinosaurs, crocodilians, and more distant amniotes, we attributed this bimodal variation to sexual dimorphism based on the extant phylogenetic bracketing approach. Documenting sexual dimorphism in fossil dinosaurs allows a better characterization and accounting of intraspecific variations, which is particularly relevant to address ongoing taxonomical and ecological questions relative to dinosaur evolution.

paleontology↗

bioRxiv2022

Taxon cycles in Neotropical mangroves

The concept of taxon cycle involves successive range expansions and contractions over time through which a species can indefinitely maintain its core distribution. Otherwise, it becomes extinct. Taxon cycles have been defined mostly for tropical island faunas, examples from continental areas are scarce and similar case studies for plants remain unknown. Most taxon cycles have been identified on the basis of phylogeographic studies, and straightforward empirical evidence from fossils is lacking. Here, empirical fossil evidence is provided for recurrent Eocene to present expansion/contraction cycles in a mangrove taxon (Pelliciera), after a Neotropical-wide study of the available pollen records. This recurrent behavior is compatible with the concept of taxon cycle from biogeographical, chronological and ecological perspectives. The biotic and abiotic drivers potentially involved in the initiation and maintenance of the Pelliciera expansion/contraction cycles are analyzed, and the ecological and evolutionary implications are discussed. Whether this could be a trend toward extinction is considered under the predictions of the taxon cycle theory. The recurrent expansion and contraction cycles identified for Pelliciera have strong potential for being the first empirically and unequivocally documented taxon cycles and likely the only taxon cycles documented to date for plants.

paleontology↗

bioRxiv2022

A natural history of networks: Higher-order network modeling for paleobiology research

Paleobiologists are increasingly employing network-based methods to analyze the complex data retrieved from geohistorical records, including stratigraphic sections, sediments, and fossil collections. However, the lack of a common framework for designing, performing, evaluating, and communicating these studies, leads to issues of reproducibility and communicability. The high-dimensional geohistorical data also raises questions about the limitations of standard network approaches, which assume independent interactions between pairs of components. Higher-order network models better suited for the complex relational structure of the geohistorical data provide an opportunity to overcome these challenges. These models can represent temporal and spatial constraints inherent to the biosedimentary record and describe higher-order interactions, capturing more accurate biogeographical, biostratigraphic, and macroevolutionary patterns. Here we describe how to use the Map Equation framework for designing higher-order network models of geohistorical data, address some practical decisions involved in modeling complex dependencies, and discuss critical methodological and conceptual issues that currently make it difficult to compare results across studies in the growing body of network-based paleobiology research. We illustrate different higher-order network representations and models, including multilayers, hypergraphs, and varying Markov times models, using case studies on gradient analysis, bioregionalization, and macroevolution, and delineate future research directions for current challenges in the emerging field of network paleobiology.

paleontology↗

bioRxiv2022

Palaeontological evidence for community-level decrease in mesopelagic fish size during Pleistocene climate warming in the eastern Mediterranean

Mesopelagic fishes are an important element of marine food webs, a huge, still mostly untapped food resource, and great contributors to the biological carbon pump, whose future under climate change scenarios are unknown. The shrinking of commercial fishes within decades has been an alarming observation, but its causes remain contended. Here, we investigate the effect of warming climate on mesopelagic fish size in the eastern Mediterranean Sea during a glacial-interglacial-glacial transition of the Middle Pleistocene (marine isotope stages 20-18; 814-712 Kyr B.P.), which included a 4 {degrees}C increase of global seawater temperature. Our results based on fossil otoliths show that the median size of lanternfishes, one of the most abundant groups of mesopelagic fishes in fossil and modern assemblages, declined by ~35% with climate warming at the community level. However, individual mesopelagic species showed different and often opposing trends in size across the studied time interval, suggesting that climate warming in the interglacial resulted in an ecological shift toward increased relative abundance of smaller-sized mesopelagic fishes due to geographic and/or bathymetric distribution range shifts, and the size-dependent effects of warming.

paleontology↗

bioRxiv2022

An armored marine reptile from the Early Triassic of South China

Sauropterygia was a taxonomically and ecomorphologically diverse clade of Mesozoic marine reptiles spanning the Early Triassic to the Late Cretaceous. Sauropterygians are traditionally divided into two groups representing two markedly different body plans - the short-necked, durophagous Placodontia and the long-necked Eosauropterygia - whereas Saurosphargidae, a small clade of marine reptiles possessing a dorsal rib-basket, is considered as the sauropterygian sister-group. However, the early evolutionary history of sauropterygians and their phylogenetic relationships with other groups within Diapsida are still incompletely understood. Here, we report a new saurosphargid from the Early Triassic of South China - Prosaurosphargis yingzishanensis gen. et sp. nov. - representing the earliest known occurrence of the clade. An updated phylogenetic analysis focussing on the interrelationships within diapsid reptiles recovers saurosphargids as nested within sauropterygians, forming a clade with eosauropterygians to the exclusion of placodonts. Furthermore, a clade comprising Eusaurosphargis and Palatodonta is recovered as the sauropterygian sister-group within Sauropterygomorpha tax. nov. The phylogenetic position of several Early and Middle Triassic sauropterygians of previously uncertain phylogenetic affinity, such as Atopodentatus, Hanosaurus, Majiashanosaurus and Corosaurus, is also clarified, elucidating the early evolutionary assembly of the sauropterygian body plan. Finally, our phylogenetic analysis recovers Testudinata and Archosauromorpha within Archelosauria, a result strongly supported by molecular data, but until now not recovered by any phylogenetic analysis using a morphology-only data set. Our study provides evidence for the rapid diversification of sauropterygians in the aftermath of the Permo-Triassic mass extinction event and emphasises the importance of broad taxonomic sampling in reconstructing phylogenetic relationships among extinct taxa.

paleontology↗

bioRxiv2022

The Three Waves: Rethinking the Structure of the first Upper Paleolithic in Western Eurasia

The Neronian is a lithic tradition recognized in the Middle Rhone Valley of Mediterranean France now directly linked to Homo sapiens and securely dated to 54,000 years ago (ka), pushing back the arrival of modern humans in Europe by 10 ka. This incursion of modern humans into Neandertal territory and the relationships evoked between the Neronian and the Levantine Initial Upper Paleolithic (IUP) question the validity of concepts that define the first H. sapiens migrations and the very nature of the first Upper Paleolithic in western Eurasia. Direct comparative analyses between lithic technology from Grotte Mandrin and East Mediterranean archeological sequences, especially Ksar Akil, suggest that the three key phases of the earliest Levantine Upper Paleolithic have very precise technical and chronological counterparts in Western Europe, recognized from the Rhone Valley to Franco-Cantabria. These trans-Mediterranean technical connections suggest three distinct waves of H. sapiens expansion into Europe between 55-42 ka. These elements support an original thesis on the origin, structure, and evolution of the first moments of the Upper Paleolithic in Europe tracing parallel archaeological changes in the East Mediterranean region and Europe.

paleontology↗

bioRxiv2022

Controls of spatial grain size and environmental variables on observed beta diversity of molluscan assemblage at a regional scale

Beta diversity, which quantifies the compositional variation among communities, is one of the fundamental partitions of biodiversity and is associated with abiotic and biotic drivers. Unveiling these drivers is essential for understanding various ecological processes in past and recent faunal communities. Although the quantification of measures of beta diversity has improved over the years, the potential dependence of beta diversity on methodological choices are relatively understudied. Here, we investigate the effect of the variable scale of sampling on different measures of beta diversity at a regional scale. The west coast of India bordering the eastern margin of the Arabian sea, presents a coastal stretch of approximately 6100km from 8-21{degrees}N. We used marine bivalve distribution data, consisting of live occurrence data from literature reports and abundance data from death assemblages collected from localities representing latitude bins. We tested if the observed variation in beta diversity is explained by variable sampling scales due to differences in bin sizes and unequal coastline length. We developed a null model to generate a beta diversity pattern with an increase in spatial scale of sampling by increasing the spatial grain size along the 14 latitude bins progressively. Our null model demonstrates that for the both live and dead dataset, the total beta diversity measured by Bray-Curtis, Whittaker and Sorenson indices decreases with increasing sampling scale. The species replacement (turnover) evaluated by Simpson index decreases and the species loss (nestedness) measured by Sorenson index increases with increasing sampling scale. A comparison between the simulated and observed beta diversity distribution using K-S test demonstrated that the observed pattern of beta diversity is significantly different from the pattern generated from the null model in both live and death assemblages. This implies that sampling alone does not generate the spatial variation in beta diversity in this region. The results show that environmental parameters such as salinity, productivity, and cyclones play a significant role in shaping the regional beta diversity along the west coast. Our study provides an approach for evaluating the effect of variable sampling scale on comparing regional beta diversity. It also highlights the importance of spatial standardization while inferring about processes driving spatial diversity changes.

paleontology↗

bioRxiv2022

Age variability and time averaging in oyster reef death assemblages

A lack of temporal context for paleoecological data from molluscan death assemblages (DAs) makes integrating them with monitoring data from living communities to inform habitat management difficult. Here we illustrate this challenge by documenting the spatial and stratigraphic variability in age and time-averaging of oyster reef death assemblages. We radiocarbon dated a total of 573 oyster shells from samples of two burial depths on 28 oyster reefs around Florida and found 1) that spatial and stratigraphic variability in DA sample ages and time-averaging are of similar magnitude, and 2) that the shallow oyster reef DAs are among the youngest and highest-resolution molluscan DAs documented to-date, with most having time-averaging estimates of decades or less. This information increases the potential usefulness of the DAs for habitat management because measured indicators can be placed in temporal context relative to monitoring data. More broadly, the results highlight the potential to obtain decadal-scale resolution from oyster bioherms in the fossil record.

paleontology↗

bioRxiv2022

Vessel wall reinforcement metrics as drought resistance indicators in angiosperm fossil wood assemblages

BackgroundPlant ecologists have developed methods to measure xylem drought resistance but these cannot be used in fossil woods. There is, however, one anatomical trait highly correlated with cavitation resistance: the squared vessel-wall thickness-to-span ratio ((t/b)2h). This metric though, could be in many cases impractical to measure in fossil samples because they often are small and sample sizes are seldom reached. Questionsare there alternative anatomical metrics that could be used instead of (t/b)2h to infer drought resistance of fossil wood assemblages? Study site and dates279 species belonging to 14 extant communities from North and South America. Three fossil wood floras from the Oligocene and Miocene of Mexico. MethodsWe calculated three alternative wall reinforcement metrics to determine their relationship with (t/b)2h and drought resistance. These are based on vessel diameter and vessel wall thickness. ResultsWe found that one of the alternative metrics ((t/b)2hydraulic mean) could potentially be used instead of (t/b)2h. The widely measured vessel wall-to-lumen ratio (VWLR), was the closest related to climate, and thus helpful in identifying broad precipitation differences among floras. VWLR and (t/b)2h might be describing slightly different ecological axes of ecological variation, with the latter associated with investment in support tissue, in addition to water availability alone. ConclusionsSome of the alternative metrics we explored can be used, in combination with other functional traits, to better describe fossil forest functional strategies.

paleontology↗

bioRxiv2022

An attempt at restoring original radiocarbon ages in collagen from bioapatite

In the literature there is a consensus that radiocarbon dating performed in bioapatite presents younger datings than those performed in collagen, thus, we propose a general regression that could be used to convert the radiocarbon dating performed in bioapatite to the original ones in collagen in fossil samples all of the world. This general regression presents several good indexes of quality, high correlation (R2 = 0.98), lower values of percent predicted error (%PE = 0.01), and the standard error of the estimate (%SEE = 25), showing that is a good tool, as the predicted values are similar to those observed. Using this regression we converted the radiocarbon datings in bioapatite to collagen made for several taxa from the Brazilian Intertropical Region, and suggest that these datings could be 1-7 Cal BP kyr older than previously thought.

paleontology↗

bioRxiv2022

The Neogene-Quaternary diversification trend in the shaping of modern Caribbean mangroves

This paper analyzes the diversification of the Neotropical mangrove flora from the Miocene to the present, using a fairly comprehensive database of 110 pollen records distributed across the whole Caribbean region. A Neogene-Quaternary diversification trend (NQDT) has been identified, characterized by an increase of 25 genera (~78%) with respect to the 7 already existing Paleogene representatives. Only two genera appeared during the Miocene and the maximum increases were observed in the Pliocene-Quaternary transition and the modernliving record. Half of the true-mangrove genera (Rhizophora, Pelliciera, Acrostichum) were already present before the Neogene and the others appeared gradually in the Oligo-Miocene (Crenea), the Early-Middle Miocene (Avicennia) and the Mio-Pliocene (Laguncularia). None of the extant associate mangrove genera were present during the Paleogene and all appeared in the Miocene (23 genera) or the Oligo-Miocene transition (3 genera), being the main responsible for the NQDT, in absolute numbers. No regional extinctions were recorded since the Miocene in the Caribbean mangroves, at the generic level. These observations should be complemented with further high-resolution quantitative studies aimed at finding potential causal relationships with climatic, eustatic and paleogeographical shifts.

paleontology↗

bioRxiv2022

Constraining the global niche suitability of the Eusuchia clade across the Cretaceous-Paleogene boundary.

The crocodiles and their close relatives, the alligators and gharials, have a compelling evolutionary history. They are a clade of great antiquity, with their most recent common ancestor emerging within the Mesozoic. However, unlike many groups of such a great age, the crocodilians have an extensive crown-group, with around two dozen extant examples. They have a limited ecomorphology, which has varied little since their inception, and their biogeography has been shown to interact closely with climate. The biogeography of crocodilians in deep time remains an outstanding question, which is complicated further by the limitations of the fossil record. The fossil record is fundamentally incomplete yet represents the most common method used to infer biogeography of organisms. The scarcity of fossil remains makes apparent absences difficult to confirm. Preservation bias will promote fossil occurrences in areas with a high sedimentation rate, which may not be the true ecological niche for a given taxon. This study uses species distribution models of extant crocodilians to infer the ecological niche of related taxa in the Maastrichtian and Danian. Models indicate a much wider latitudinal range than is observed among extant examples, and the invasion of new ecospace following the end-Cretaceous mass extinction. In addition, we find that while temperature is of significance to crocodilian biogeography, it is precipitation that is the most influential climatic variable.

paleontology↗

bioRxiv2022

Trilobite moulting behaviour variability had little association with morphometry

Trilobite moult assemblages preserved in the fossil record show high variability in moulting behaviour and their resulting moult configurations. The reasons for this variability, and the impacts it might have had on their evolutionary trajectories, are unknown and have rarely been investigated quantitatively. A large dataset of trilobite moult morphometric measurements is presented and statistically analysed for associations between moulting behaviour and morphometry. Results indicate little significant statistical association between the two; only between moulting behaviour (usually generalised moult configuration) and the variances and means of thoracic tergite number, thorax length, and pygidium width. Anterior cranidium width, cranidium length, cephalothoracic joint width, thorax width, pygidium length, and total body length all have non-significant associations with moulting behaviour. Moult specimens showing inversion of the librigenae generally have more thoracic tergites, a correspondingly longer thorax, and a narrower pygidium. Thoracic tergite count and pygidium measurements may have multimodal distributions. Principal Components Analyses and Non-Metric Multidimensional Scaling analyses suggest minor differences in the extent of morphometric variation for specimens showing different moulting behaviours, but little difference in the region of morphospace they occupy. This may indicate that trilobite species using Salters mode of moulting had more constrained morphologies, potentially related to facial suture fusion in some groups. Overall, these results do not suggest a strong association between moulting behaviour variation and morphometry in trilobites, leaving open for further study the mystery of why trilobites were so variable in their moulting, and whether this contributed to their long evolutionary reign or ultimate extinction. PLAIN LANGUAGE SUMMARYTrilobites were an important and globally abundant group of arthropods (animals with an exoskeleton and jointed limbs) that lived ~521-251 million years ago. The exoskeletons of arthropods are crucial because they provide protection against predators and parasites, but also restrict their growth. All living and extinct arthropods must therefore periodically moult (shed) their exoskeletons; an incredibly risky event during which many individuals die. Due to its importance, it is presumed that exoskeleton moulting impacted the broad-scale evolution of arthropod morphology (their physical characteristics), behaviour, and ecology. Trilobite moults are preserved in great number in the fossil record, and this can tell us much about their moulting behaviour. Additionally, trilobites appear to be unique in showing many different moulting behaviours. However, we do not know why trilobites were so variable in their moulting behaviour, or what impact this had on their evolution. In this study, a large dataset of trilobite moulting behaviours and their body proportion (morphometry) measurements is presented and analysed to answer: Was variability in trilobite moulting behaviour related to differences in their morphometry? The results suggest that there was little association between the moulting behaviours shown by trilobites and their morphometry. Species showing the different moulting behaviours had overall similar morphologies, although for one moulting behaviour this seemed more limited. Only thorax length and segmentation (the central part of the body), and pygidium ( tail) width, significantly differed between species showing the different moulting behaviours. This study does not indicate a strong relationship between moulting behaviour and morphology in trilobites. This is unexpected, and leaves open the mystery of trilobite moulting variability.

paleontology↗

bioRxiv2022

Shape analysis of Iron Age sheep astragali suggests west-to-east morphotype diffusion in the southern Levant

The movement of livestock across the Mediterranean is well-documented in the Neolithic era, but its significance during subsequent periods has received less attention. This study explores potential evidence for maritime connections between sheep populations in the Iron Age eastern Mediterranean by analyzing astragal bones from four coastal and inland sites in Israel and Cyprus. Employing an established geometric morphometric protocol, we investigated the hypothesis that intra-site morphological variability is higher in coastal sites, reflecting greater genetic diversity in the livestock populations. While our findings support this hypothesis, the conclusions are constrained by contextual and sample size limitations.

paleontology↗

bioRxiv2023

Axial regionalization in Tiktaalik roseae and the origin of quadrupedal locomotion

The origin of quadrupedal locomotion in tetrapods entailed the evolution of a regionalized axial skeleton with sacral ribs. These ribs provide linkage between the pelvis and vertebral column and contribute to body support and propulsion by the hind limb. The closest relatives of limbed vertebrates are not known to possess such a connection and, therefore, have typically been described as primarily supporting their bodies against the substrate with pectoral fins. However, data on the axial skeletons of stem tetrapods are sparce, with key features of specimens potentially concealed by matrix. Here we provide micro-computed tomography data of the axial skeleton of Tiktaalik roseae and show that its vertebrae and ribs are regionalized along the craniocaudal axis, including expanded and ventrally curved ribs in the sacral region. The sacral ribs would have contacted the expanded iliac blade of the pelvis in a soft tissue connection. No atlas-axis complex is observed, however the basioccipital-exoccipital complex is deconsolidated from the rest of the neurocranium, suggesting increased mobility at occipital-vertebral junction. Thus, axial regionalization that allowed for innovations in head mobility, body support and buttressing the pelvic fin evolved prior to the origin of limbs.

paleontology↗

bioRxiv2023

The dual role of the angiosperm radiation on insect diversification

Most of the animal pollination is realized by insects, interactions between them and flowering plants have been hypothesized to be important drivers of diversification. Yet, there is weak support for coevolutionary diversification in plant-pollinator interactions. Macroevolutionary studies on insect and plant diversities support the hypothesis that angiosperms evolved after an insect diversity peak in the Early Cretaceous, suggesting that gymnosperm pollinators may have been accessible for angiosperms when they evolved. We examined fossil and phylogenetic evidence documenting this hypothesis and provide new clues on the impact of angiosperm radiation on insect diversification. Using the family-level fossil record of insects and a Bayesian process-based approach, we estimated diversification rates and the role of six different variables on insect macroevolutionary history. We found that, among the six tested variables, angiosperms had a dual role that has changed through time with an attenuation of insect extinction in the Cretaceous and a driver of insect origination in the Cenozoic. However, increasing insect diversity, spore plants and global temperature also showed strong positive correlation with both origination and extinction rates of insects, suggesting that different drivers had important effect on insect evolution, not just angiosperms, which would deserve further studies.

paleontology↗

bioRxiv2023

Micro- to nano-scale investigation of Precambrian metasediments: biogenicity and preservation in the 3.22 Ga Moodies Group (Barberton Greenstone Belt, S. Africa) and the 2.46 Ga Brockman Iron Formation (Hamersley Basin, W. Australia).

Precambrian metasediments provide a unique archive for understanding Earths earliest biosphere, however traces of microbial life preserved in ancient rocks are often controversial. In this study we leveraged several micro- to nano-scale techniques to study filamentous structures previously reported in clastic sediments of the 3.22 Ga Moodies Group, Barberton Greenstone Belt, S. Africa. We performed petrographic, mineralogical, electron microprobe, confocal fluorescence and electron microscopy analyses of these structures in order to evaluate their biogenicity and syngenecity. We also examined drill core samples of deep-water iron formations from the 2.46 Ga Joffre member of the Brockman Iron Formation (Hamersley Basin, W. Australia) to better understand their potential biogenicity. In both cases, we aimed to resolve primary vs. secondary mineral assemblages and their relation to filamentous or sedimentary structures. In the Moodies Group samples, filamentous structures were resolved by confocal imaging and revealed to be crosscut by later metamorphic phases, highlighting their syngenetic nature. Three-dimensional imaging reveals that while the filamentous structures are not necessarily associated with grain boundaries (e.g., as organic coatings), they form both sheets and filaments, complicating their interpretation but not ruling out a biological origin. No organic microstructures appeared to be preserved in our Dales Gorge samples. We also examined the possible application of electron paramagnetic resonance spectroscopy (EPR) to carbonaceous matter in ancient silica-rich matrices, similar to Bourbin et al. (2013), using samples from the Brockman iron formation. While resonance associated with organic matter was largely unresolvable in the Brockman iron formation samples due to their low organic matter contents, large effects on the EPR spectra were apparent stemming from the presence of magnetic iron minerals, highlighting the need to carefully consider sample composition in EPR analyses targeting ancient organic matter. Collectively, this study highlights the added value of micro- to nano-scale techniques as applied to Precambrian metasediments containing traces of ancient life, for example in revealing the pre-metamorphic emplacement and three-dimensional structure of filaments in the Moodies Group, but also the potential drawbacks and pitfalls, such as the case of strong magnetic mineral interference in EPR analysis of organic matter in trace abundance in the Dales Gorge.

paleontology↗

bioRxiv2023

Cementochronology using synchrotron radiation tomography to determine age at death and developmental rate in the holotype of Homo luzonensis

Homo luzonensis, a fossil hominin from the Philippines, is smaller than modern humans. At present, very little is known about the life history of this species. Cementochronology can answer life history questions, but usually involves destructive sampling. Here, we use synchrotron radiation to count the yearly cement lines of teeth belonging to a single individual. This approach allows us to determine that this individual was likely 31 years old at time of death and apparently had a developmental pattern comparable to chimpanzees. To our knowledge, this is the first time that cementochronology using synchrotron radiation tomography is used for life history and age-at-death estimation.

paleontology↗