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bioRxiv2023

Identification of Late Pleistocene and Holocene fossil lizards from Hall's Cave and a primer on morphological variation in North American lizard skulls

Fossil identification practices have a profound effect on our interpretation of the past because these identifications form the basis for downstream analyses. Therefore, well-supported fossil identifications are paramount for examining the impact of past environmental changes on populations and communities. Here we apply an apomorphic identification framework in a case study identifying fossil lizard remains from Halls Cave, a late Quaternary fossil site located in Central Texas, USA. We present images and descriptions of a broad comparative sample of North American lizard cranial elements and compile new and previously reported apomorphic characters for identifying fossil lizards. Our fossil identifications from Halls Cave resulted in a minimum of 11 lizard taxa, including five lizard taxa previously unknown from the site. Most of the identified fossil lizard taxa inhabit the area around Halls Cave today, but we reinforce the presence of an extirpated species complex of horned lizard. A main goal of this work is to establish a procedure for making well-supported fossil lizard identifications across North America. The data from this study will assist researchers endeavoring to identify fossil lizards, increasing the potential for novel discoveries related to North American lizards and facilitating more holistic views of ancient faunal assemblages.

paleontology↗

bioRxiv2023

Ophidian physique: the capacity of middle trunk vertebral shape for quantitative taxonomic delimitation in snakes

Skeletal specializations in snakes have resulted in incredible locomotive adaptability, including oft-overlooked vertebral complexity. Snake vertebrae are usually identified via qualitative descriptions of morphological traits; however, identifying and describing snake vertebrae in a scientifically replicable way has long hindered fossil snake research, where attempts to identify between or within snake groups can be onerous. Here, we build a framework of extant snake middle trunk vertebral shape using 2D geometric morphometrics (GMM) and quantitative methods to explore the viability of using these tools to assign and identify snake trunk vertebrae taxonomically and ecologically. We use 23 landmarks to evaluate anterior vertebral shape variation in 504 snake trunk vertebrae representing 189 species across 11 families for delimiting taxonomy and primary foraging habitat. We found that snake vertebral shape variation of overall proportions and articular surfaces contained statistically significant taxonomic and ecomorphological information useful for group assignment. Differences in primary foraging habitat also resulted in similar morphological trends within taxonomic groups in shape space. We then used linear discriminant functions to test the reliability of taxonomic assignments based on the shape captured by our landmark scheme. Analysis of the full dataset had high overall accuracy for family and subfamily, but only moderate success for genus, species, and primary foraging habitat. When applied to a single subfamily, overall accuracy greatly increased for genus and primary foraging habitat, implying that iterative application of this method may improve results. This study presents the framework for a new replicable method to supplement qualitative morphological descriptions of taxa. We recommend that GMM is best employed alongside qualitative descriptions for the optimal and reproducible delimitation of snake vertebrae. Finally, this method will allow non-expert diagnosticians to have more confidence in identifying fossil snake vertebrae, helping increase the number of snake fossils identified in museum collections.

paleontology↗

bioRxiv2023

Lack of early animal fossils: insights from taphonomic experiments on placozoans and their traces

Placozoa are simple two-layered multicellular animals. Can such a simple animal preserve in the fossil record? The results of our taphonomic experiments showed that it is chemically possible; however, the chances of the presevation are negligible for two reasons. Firstly, the resistance of living Trichoplax to lethal factors turned out to be quite high. Secondly, post-mortem changes in the body of Trichoplax preclude preservation. We observed these changes for the first time: their bodies immediately disintegrated into a cloud of individual dead cells, apparently unrecognizable in the fossil record. We hypothesized that the absence of a basement membrane, which unites each cell layer into the epithelia, is a key factor in this dramatic disintegration. This hypothesis adds an option to the explainations of the gap between the time of emergence of metazoan body fossils and the reconstructed time of metazoan divergence from a single-celled ancestor. However, it is theoretically possible to find ichnofossils of Trichoplax-like locomotion. For the first time, we observed traces of Trichoplax on a soft substrate and identified a previously unknown type of traces. They were 3D chains of compacted round lumps of the substrate, similar in some features to the Precambrian meniscus ichnofossils.

paleontology↗

bioRxiv2023

Longer mandible or nose? Co-evolution of feeding organs in early elephantiforms

The long-trunked elephantids underwent a significant evolutionary stage characterized by an exceptionally elongated mandible. The initial elongation and subsequent regression of the long mandible, along with its co-evolution with the trunk, present an intriguing issue that remains incompletely understood. Through comparative functional and eco-morphological investigations, as well as feeding preference analysis, we reconstructed the feeding behavior of major groups of longirostrine elephantiforms. In the Platybelodon clade, the rapid evolutionary changes observed in the narial region, strongly correlated with mandible and tusk characteristics, suggest a crucial evolutionary transition where feeding function shifted from the mandible to the trunk, allowing proboscideans to expand their niches to more open regions. This functional shift further resulted in elephantids relying solely on their trunks for feeding. Our research provides insights into how unique environmental pressures shape the extreme evolution of organs, particularly in large mammals that developed various peculiar adaptations during the late Cenozoic global cooling trends.

paleontology↗

bioRxiv2023

The three-dimensionally articulated oral apparatus of a Devonian heterostracan sheds light on feeding in Palaeozoic jawless fishes

Attempts to explain the origin and diversification of vertebrates have commonly invoked the evolution of feeding ecology, contrasting the passive suspension feeding of invertebrate chordates and larval lampreys with active predation in living jawed vertebrates. Of the extinct jawless vertebrates that phylogenetically intercalate these living groups, the feeding apparatus is preserved only in the early diverging stem-gnathostome heterostracans and its anatomy remains poorly understood. Here we use X-ray microtomography to characterise the feeding apparatus of the pteraspid heterostracan Rhinopteraspis dunensis (Roemer, 1855). We show that the apparatus is composed of thirteen plates arranged approximately bilaterally, the majority of which articulate from the postoral plate. Our reconstruction of the apparatus shows that the oral plates would have been capable of movement within the dorso-ventral plane, but their degree of movement was limited. The functional morphology of the apparatus in Rhinopteraspis precludes all proposed interpretations of feeding except for suspension/deposit feeding and we interpret the apparatus as having served primarily to moderate the oral gape. This is consistent with evidence that at least some early jawless gnathostomes were suspension feeders and runs contrary to macroecological scenarios that envisage early vertebrate evolution as characterised by a directional trend towards increasingly active food acquisition.

paleontology↗

bioRxiv2023

The pharynx of the iconic stem-group chondrichthyan Acanthodes (Agassiz, 1833) revisited with micro computed tomography.

Acanthodes has long been the primary source of information on the pharyngeal skeleton of acanthodians, a stem-group chondrichthyan grade. Because of this its anatomy has played an outsized role in attempts to understand the evolution of the jawed vertebrate pharynx and the clade as a whole. However, the anatomy of the pharynx of Acanthodes remains poorly understood and subject to several competing interpretations. We use computed tomography (CT) to image the articulated pharyngeal skeletons of three specimens of Acanthodes confusus from Lebach, Germany. Acanthodes had a melange of osteichthyan-like and chondrichthyan-like morphologies in its pharyngeal skeleton. Like other stem-chondrichthyans, Acanthodes had a basihyal with no hypohyals, and four pairs of posteriorly oriented pharyngobranchials. Like osteichthyans, Acanthodes possessed an interhyal, but lacked the separate infra- and supra-pharyngobranchial elements present in osteichthyans and the crown-chondrichthyan Ozarcus. Using this new data we build and animated a digital 3D model of the pharyngeal endoskeleton in Acanthodes, showing that the jaws would have swung outwards during the opening cycle, increasing the anteriorly facing area of the gape for suspension feeding. These new data provide a more definitive picture of the anatomy of a taxon that has long been of great significance in early vertebrate palaeontology.

paleontology↗

bioRxiv2023

Age-dependent extinction and the neutral theory of biodiversity

Red Queen (RQ) theory states that adaptation does not protect species from extinction because their competitors are continually adapting alongside them. RQ was founded on the apparent independence of extinction risk and fossil taxon age, but analytical developments have since demonstrated that age-dependent extinction is widespread, usually most intense among young species. Here we develop ecological neutral theory as a general framework for modeling fossil species survivorship under incomplete sampling. We show that it provides excellent fit to a high-resolution dataset of species durations for Paleozoic zooplankton, and more broadly can account for age-dependent extinction seen throughout the fossil record. Unlike widely used alternative models, the neutral model has parameters with biological meaning, thereby generating testable hypotheses on changes in ancient ecosystems. The success of this approach suggests novel interpretations of mass extinctions and of scaling in eco-evolutionary systems. Intense extinction among young species does not necessarily refute RQ or require a special explanation, but can instead be parsimoniously explained by neutral dynamics operating across species regardless of age. Significance StatementRed Queen theory predicts that competition among species should cause extinction risk to be independent of species age, but recent analyses have refuted this central prediction. To fill the resulting theoretical vacuum, we used ecological neutral theory to build a model of the lifespans of incompletely sampled species evolving under zero-sum competition. This model predicts survivorship among fossil zooplankton with surprising accuracy and accounts for empirical deviations from the predictions of Red Queen more generally. A neutral model of background extinction allows for interpreting survivorship curves in terms of biological process, suggests a novel understanding of mass extinctions, and supports a role for competition in extinction.

paleontology↗

bioRxiv2023

Forensic Facial Approximation of Achondroplastic Dwarf from Medieval Cemetery in Central Europe

Achondroplasia (ACH, achondroplastic dwarfism) represents the most common form of skeletal dysplasia, occurring in c. 4 out of every 100,000 births. This study presents a computer-based facial approximation of the skull of a male individual suffering from ACH, who died at 30-45 years of age and was buried in ekno, Poland between the 9th and 11th centuries AD. For the approximation procedure, soft tissue data from CT scans and ultrasonic measurements performed on living individuals were used. Additionally, the anatomical deformation technique was applied to arrive at the most reliable reconstruction of the dwarfs appearance. To our knowledge, this is the first recreation of a person with achondroplasia, and one of the few showing a head of an individual suffering from a hereditary disease, with dimensions and shape differing from the population average values. Highlights- Forensic facial approximation of an achondroplastic dwarf from 9th-11th century AD has been performed as the first in the world - The applied procedure included CT of a virtual donor - Anatomical deformation technique allowed to extract the endocast, revealing a large volume of the endocranium - Few measurements applied to the facial skeleton proved successful in identification of a person suffering from achondroplasia

paleontology↗

bioRxiv2023

Approaches to Species Distribution Modelling in Dinosaurs and Other Fossil Organisms

SDM describes a family of methods aiming to predict the geographic distribution of organisms using environmental data such as climate variables. It is a versatile tool in estimating ecological communities and interactions both spatially and through time. However, it has had limited utility in predicting the geographic distribution of fossil organisms. Due to preservation and sampling biases, fossil data does not satisfy the assumptions of species distribution models. Here is presented an analysis proposing a new methodology, which substitutes the conventional pseudoabsence data for fossil occurrences from non-target species. This approach eliminates variation in preservation and sampling, and returns a SDM which performs better than a conventional example. This model concludes that the ceratopsian Triceratops may have been widespread across North America, and beyond the region where its fossils have been recovered. The geographic distribution of Triceratops appears to have been governed by seasonality in temperature and temperature of the coldest month.

paleontology↗

bioRxiv2023

Life in a Central European warm-temperate to subtropical open forest: paleoecology of the rhinocerotids from Ulm-Westtangente (Aquitanian, early Miocene, Germany)

The locality of Ulm-Westtangente yielded the richest vertebrate fauna from the Aquitanian (23.03 to 20.44 Mya; early Miocene) of Germany. Its dating to the Mammal Neogene Zone 2a, a turnover in Cenozoic climate, makes it a crucial source for the understanding of faunal, palaeoecological and palaeoenvironmental specifics of the European Aquitanian. However, if most taxa from Ulm-Westtangente have been studied, very little or nothing has been done on the large herbivores and notably the two rhinocerotids Mesaceratherium paulhiacense and Protaceratherium minutum. Here, we used a multi-proxy approach to investigate the paleoecology of these two species. The remains of the smaller species P. minutum (body mass based on teeth: 442 to 667 kg) are twice as abundant as those of the larger M. paulhiacense (1687 to 2576 kg), but both display a similar age structure with around 10 % of juveniles, 20 % of subadults and 70 % of adults. Results from mesowear, microwear, and carbon isotopes indicate different feeding preferences for the two species at Ulm-Westtangente: both were C3 feeders but M. paulhiacense had a more abrasive diet and was probably a mixed feeder inhabiting a wider range of habitats. Both species had similar mortality curves revealing four mortality peaks correlated with life events: birth or shortly after (age classes I and II), juvenile diseases (IV), weaning (VI-VII), and sexual maturity (IX-X). They were also similarly affected by hypoplasia, with about 17 % of teeth bearing at least one defect, but the most affected loci did not always correlate with the events highlighted by the mortality curves. Our study on rhinocerotids also yielded new paleoenvironmental insights, such as the mean annual temperature (19.2 {degrees}C), confirming the warm-temperate to subtropical conditions previously inferred.

paleontology↗

bioRxiv2023

Femora Nutrient Foramina and Aerobic Capacity in Giant Extinct Xenarthrans

Nutrient foramina are small openings in the periosteal surface of long bones that traverse the cortical layer and reach the medullary cavity. They are important for the delivery of nutrients and oxygen to bone tissue, and are crucial for the repair and remodeling of bones over time. The nutrient foramina in the femurs diaphysis are related to the energetic needs of the femur, and have been shown to be related to the maximum metabolic rate (MMR) of taxa. Here, we investigate the relationship between nutrient foramen size and body mass as a proxy to the aerobic capacity of taxa in living and extinct xenarthrans, including living sloths, anteaters, and armadillos, as well as extinct xenarthrans such as glyptodonts, pampatheres, and ground sloths. Sixtynine femora were sampled, including 19 from extant taxa and 50 from extinct taxa. We obtained the blood flow index (Qi) based on foramina area and performed PGLS and phylogenetic ANCOVA in order to explore differences among mammalian groups. Our results show that among mammals, taxa commonly associated with lower metabolism like marsupials and living xenarthrans showed relatively smaller foramina, while the foramina of giant extinct xenarthrans like ground sloths and glyptodonts overlapped with non-xenarthran placentals. Consequently, Qi estimations indicated aerobic capacities comparable to other placental giant taxa like elephants or some ungulates. Furthermore, the estimation of the MMR for fossil giant taxa showed similar results, with almost all taxa showing high values except for those for which strong semi-arboreal or fossorial habits have been described. Moreover, the results are compatible with the diets predicted for extinct taxa, which indicate a strong consumption of grass similar to ungulates and in contrast to the folivorous or insectivorous diets of extant xenarthrans. The ancestral reconstruction of the MMR values indicated a lack of a common pattern for all xenarthrans, strongly supporting the occurrence of low metabolic rates in extant forms due to their particular dietary preferences and arboreal or fossorial habits. Our results highlight the importance of considering different evidence beyond the phylogenetic position of extinct taxa, especially when extinct forms are exceptionally different from their extant relatives. Future studies evaluating the energetic needs of giant extinct xenarthrans should not assume lower metabolic rates for these extinct animals based solely on their phylogenetic position and the observations on their extant relatives.

paleontology↗

bioRxiv2023

Convergent evolution of ventral adaptations for enrollment in trilobites and extant euarthropods

The ability to enroll for protection is an effective defensive strategy that has convergently evolved multiple times in disparate animal groups ranging from euarthropods to mammals. Enrollment is an evolutionary staple of trilobites, and their biomineralized dorsal exoskeleton offers a versatile substrate for the evolution of interlocking devices. However, it is unknown whether trilobites also featured ventral adaptations for enrolment. Here, we report ventral exoskeletal adaptations that facilitate enrollment in exceptionally preserved trilobites from the Upper Ordovician Walcott-Rust Quarry in New York State, USA. Walcott-Rust trilobites reveal the intricate three-dimensional organization of the non-biomineralized ventral anatomy preserved as calcite casts, including the spatial relationship between the articulated sternites (i.e., ventral exoskeletal plates) and the wedge-shaped protopodites. Enrollment in trilobites is achieved by ventrally dipping the anterior margin of the sternites during trunk flexure, facilitated by the presence of flexible membranes, and the close coupling of the wedge-shaped protopodites. Comparisons with the ventral morphology of extant glomerid millipedes and terrestrial isopods reveal similar mechanisms used for enrollment. The wedge-shaped protopodites of trilobites closely resemble the gnathobasic coxa/protopodite of extant horseshoe crabs. We propose that the trilobites wedge-shaped protopodite simultaneously facilitates tight enrollment and gnathobasic feeding with the trunk appendages.

paleontology↗

bioRxiv2023

Evolution of hind limb morphology of Titanosauriformes (Dinosauria, Sauropoda) via 3D Geometric Morphometrics reveals wide-gauge posture as an exaptation for gigantism

The sauropod hind limb was the main support that allowed their gigantic body masses and a wide range of dynamic stability adaptations. It was closely related to the position of the centre of masses of their multi-ton barrel-shaped bodies, and experienced one of the most noticeable posture changes during macronarian evolution. Deeply branched macronarians achieved increasingly arched hind limbs in what is known as wide-gauge posture. However, it is not clear if this evolutionary trend is related to the evolutionary cascade toward gigantism even though some titanosaurians were the largest terrestrial vertebrates that ever existed. We tested evolutionary changes in hind limb morphology in the Macronaria phylogenetic tree by 3D geometric morphometrics. The macronarian hind limb does become progressively more arched toward deeply-branched groups, specifically Saltasauridae. However, there is morphological convergence between different macronarian subclades. Wide-gauge posture does not correlate with changes in body size deeper in the macronarian evolutionary tree, and acted as an exaptation to gigantism. Despite some titanosaurian subclades becoming some of the largest vertebrates, there is not a statistically-significant trend toward a particular body size but we identify a phyletic body size decrease in Macronaria.

paleontology↗

bioRxiv2023

Multiple origins of cephalic sutures in trilobites and their relatives

Euarthropods are an extremely diverse phylum in the modern, and have been since their origination in the early Palaeozoic. They grow through moulting the exoskeleton (ecdysis) facilitated by breaking along lines of weakness (sutures). Artiopodans, a group that includes trilobites and their non-biomineralizing relatives, dominated arthropod diversity in benthic communities during the Palaeozoic. Most trilobites - a hyperdiverse group of tens of thousands of species - moult by breaking the exoskeleton along cephalic sutures, a strategy that has contributed to their high diversity during the Palaeozoic. However, the recent description of similar sutures in early diverging non-trilobite artiopodans mean that it is unclear whether these sutures evolved deep within Artiopoda, or convergently appeared multiple times within the group. Here we describe new well-preserved material of Acanthomeridion, a putative early diverging artiopodan, including hitherto unknown details of its ventral anatomy and appendages revealed through CT scanning, highlighting additional possible homologous features between the ventral plates of this taxon and trilobite free cheeks. We used three coding strategies treating ventral plates as homologous to trilobite free cheeks, to trilobite cephalic doublure, or independently derived. If ventral plates are considered homologous to free cheeks, Acanthomeridion is recovered sister to trilobites however dorsal ecdysial sutures are still recovered at many places within Artiopoda. If ventral plates are considered homologous to doublure or non-homologous, then Acanthomeridion is not recovered as sister to trilobites, and thus the ventral plates represent a distinct feature to trilobite doublure/free cheeks.

paleontology↗

bioRxiv2023

Macroevolutionary drivers of morphological disparity in the avian quadrate

In birds, the quadrate bone acts as a hinge between the lower jaw and the skull, playing an important role in cranial kinesis. As such, the evolution of avian quadrate morphology may plausibly be assumed to have been influenced by selective pressures related to feeding ecology. However, variation in quadrate morphology across living birds and its potential relationship with ecology have never been quantitatively characterised. Here, we used three-dimensional geometric morphometrics and phylogenetic comparative methods to quantify morphological variation of the quadrate and its relationship with an array of key ecological features across 200 bird species covering all major extant lineages. We found non-significant associations between quadrate shape and several aspects of feeding and foraging ecology across different scales of phylogenetic comparison. By contrast, allometry and phylogeny exhibit stronger relationships with quadrate shape than other ecological features. We show that the avian quadrate evolves as an integrated unit and exhibits strong associations with the morphologies of neighbouring bones. Our results collectively suggest a macroevolutionary scenario in which the shape of the quadrate evolved jointly with other elements of the avian kinetic system, with the major lineages of birds exploring alternative quadrate morphologies--highlighting the potential diagnostic value of quadrate morphology in investigations of fossil bird systematics.

paleontology↗

bioRxiv2023

GIRAFFOIDS FROM THE SIWALIKS OF PAKISTAN

Although today they occur in Africa, during the Miocene Giraffoids were widespread in Eurasia. We describe the giraffoid faunas found in the Siwaliks of Pakistan. These faunas are extremely rich and provide with several new giraffoid taxa that are morphologically different to what taxa known before and give new insights in the taxa. Non-Siwalik localities that contribute key information are: Fort Ternan, Kalodirr, Tung Gur, Gebel Zelten, Gebel Hamrin and Bou Hanifia. (1) The Palaoemerycidae are distinct with ossicones and an occipital horn. The list of taxa includes five new palaeomerycids: Tauromeryx canteroi nov. sp., Charis gratia nov. gen. sp. nov., Fovea fossata nov. gen. sp. nov, Goniomeryx flynni gen. nov. sp. nov., and Lateralia morgani nov. gen. nov. sp. nov.; (2) new climacoceratids: Vittoria soriae gen nov. sp nov. Orangemeryx badgleyi nov. sp. We also define two new ranks within the Climacoceridae family: the Climacocerinae and the Prolibytheriinae. (3) Preliminary systematics suggest that Giraffidae can be subdivided into two clades: the long and the short neck groups. The Siwaliks sample a total of twelve different giraffids: Progiraffa exigua, Giraffokeryx punjabiensis, Ua pilbeami, Orea leptia, Injanatherium hazimi, Giraffa punjabiensis, Giraffa sivalensis, Decennatherium asiaticum, Bramatherium megacephalum, Bramatherium perminese, Bamiscus micros, and Sivatherium giganteum. Palaeotragus germanii and Bohlinia tungurensis are new determinations. Progiraffinae and Bramatheriinae as new subfamilies. The subfamilies of Giraffidae seem to hold as isolated evolutionary silos. They are: Progiraffinae, Giraffokerycinae, Okapiinae, Bohlininae, Giraffinae, Palaeotraginae, Samotheriinae, Bramatheriinae and Sivatheriinae. It is hard to connect these subfamilies as they most appear around 15 Ma.

paleontology↗

bioRxiv2023

Alasemenia, the earliest ovule with three wings and without cupule

The ovules or seeds (fertilized ovules) with wings are widespread and especially important for wind dispersal. However, the earliest ovules in the Famennian of the Late Devonian are rarely known about the dispersal syndrome and usually surrounded by a cupule. From Xinhang, Anhui, China, we report a new taxon of Famennian ovules, Alasemenia tria gen. et sp. nov. Each ovule possesses three integumentary wings evidently extending outwards, folding inwards along abaxial side and enclosing most part of nucellus. The ovule is borne terminally on smooth dichotomous branches and lacks a cupule. Alasemenia suggests that the integuments of the earliest ovules without a cupule evolved functions in wind dispersal and probable photosynthetic nutrition. It indicates that the seed wing originated earlier than other wind dispersal mechanisms such as seed plume and pappus, and that three- or four-winged seeds were followed by seeds with less wings. Mathematical analysis shows that three-winged seeds are more adapted to wind dispersal than seeds with one, two or four wings under the same condition.

paleontology↗

bioRxiv2023

Estimating body volumes and surface areas of animalsfrom cross-sections

Body mass and surface area are among the most important biological properties, but such information are lacking for some extant organisms and all extinct species. Numerous methods have been developed for body size estimation for this reason. There are two main categories of mass-estimating methods: volumetric-density approaches and extant-scaling approaches. In this paper, a new 2D volumetric-density approach named cross-sectional method is presented. Cross-sectional method integrates biological cross-sections to obtain volume and surface area accurately. Unlike all previous 2D methods, cross-sectional method processes true cross-sectional profiles directly rather than approximating. Cross-sectional method also has the advantage over others that it can deal with objects with gradually changing cross-sections. It generates very accurate results, with errors always lower than 2% in all cases tested.

paleontology↗