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in category paleontology

183 results found. For more information, click each entry to expand.

1: Dinosaur bonebed amber from an original swamp forest soil
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Posted 16 Sep 2021

Dinosaur bonebed amber from an original swamp forest soil
569 downloads bioRxiv paleontology

Sergio Álvarez-Parra, Ricardo Pérez-de la Fuente, Enrique Peñalver, Eduardo Barrón, Luis Alcalá, Jordi Pérez-Cano, Carles Martín-Closas, Khaled Trabelsi, Nieves Meléndez, Rafael López Del Valle, Rafael P Lozano, David Peris, Ana Rodrigo, Víctor Sarto i Monteys, Carlos A Bueno-Cebollada, César Menor-Salván, Marc Philippe, Alba Sánchez-García, Constanza Peña-Kairath, Antonio Arillo, Eduardo Espílez, Luis Mampel, Xavier Delclòs

Dinosaur bonebeds with amber content, yet scarce, offer a superior wealth and quality of data on ancient terrestrial ecosystems. However, the preserved palaeodiversity and/or taphonomic characteristics of these exceptional localities had hitherto limited their palaeobiological potential. Here we describe the amber from the Lower Cretaceous dinosaur bonebed of Arino (Teruel, Spain) using a multidisciplinary approach. Amber is found in both a root layer with amber strictly in situ and a litter layer namely composed of aerial pieces unusually rich in bioinclusions, encompassing 11 insect orders, arachnids, and a few plant and vertebrate remains, including a feather. Additional palaeontological data - charophytes, palynomorphs, ostracods - are provided. Arino arguably represents the most prolific and palaeobiologically diverse locality in which fossiliferous amber and a dinosaur bonebed have been found in association, and the only one known where the vast majority of the palaeontological assemblage suffered no or low-grade pre-burial transport. That has enabled unlocking unprecedentedly complete and reliable palaeoecological data out of two complementary windows of preservation from the same site.

2: A crocodylian-style cloaca in a non-avialan dinosaur
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Posted 12 Oct 2020

A crocodylian-style cloaca in a non-avialan dinosaur
199 downloads bioRxiv paleontology

Phil R. Bell, Michael Pittman, Thomas G. Kaye, Christophe Hendrickx

Our knowledge of the reproductive biology of dinosaurs covers a range of aspects, from brooding behaviour to nesting style and the timing of sexual maturity. Yet, the basic anatomy and function of the cloaca in non-avialan dinosaurs remains unknown. Here, we describe the outer morphology of the only known non-avialan dinosaur cloaca, preserved in an exceptional specimen of the early-diverging ceratopsian dinosaur Psittacosaurus . We clarify the position of the cloaca with respect to the ischia and caudal vertebrae and document the scales immediately adjacent to the abdomen and tail. We find that the cloaca is from a near-sexually mature subadult individual and is most similar to the cloaca of crocodylians, to the exclusion of lepidosaurians and birds. However, the sex of SMF R 4970 could not be determined as the cloaca and the rest of the specimen does not yield any sexually dimorphic information. This study highlights the ongoing role of exceptional specimens in providing rare soft tissues that help to bridge longstanding gaps in our knowledge of the basic biology of dinosaurs and other extinct reptiles. ### Competing Interest Statement The authors have declared no competing interest.

3: Morphometric Analysis of Lungfish Endocasts Elucidates Early Dipnoan Palaeoneurological Evolution
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Posted 15 Sep 2021

Morphometric Analysis of Lungfish Endocasts Elucidates Early Dipnoan Palaeoneurological Evolution
151 downloads bioRxiv paleontology

Alice M Clement, Tom J Challands, Richard Cloutier, Laurent Houle, Per E Ahlberg, Shaun P Collin, John A Long

Lungfish (Dipnoi) are lobe-finned fish (Sarcopterygii) that have persisted for over 400 million years from the Devonian Period to present day. They are the extant sister group to tetrapods and thus have the ability to provide unique insight into the condition of the earliest tetrapods as well as their own evolutionary history. The evolution of their dermal skull and dentition is relatively well understood, but this is not the case for the central nervous system. While the brain itself has very poor preservation potential and is not currently known in any fossil lungfish, substantial indirect information about it and associated structures such as the inner ears can be obtained from the cranial endocast. However, before the recent development of X-ray tomography as a palaeontological tool, these endocasts could not be studied non-destructively, and few detailed studies were undertaken. Here we describe and illustrate the endocasts of six Palaeozoic lungfishes (Iowadipterus halli, Gogodipterus paddyensis, Pillararhynchus longi, Griphognathus whitei, Orlovichthys limnatis, and Rhinodipterus ulrichi) from tomographic scans. We combine these with six previously described lungfish endocasts (4 fossil and 2 recent taxa), also based on tomographic studies, into a 12-taxon data set for multivariate morphometric analysis using 17 variables. We find that the olfactory region appears to be more highly plastic than the hindbrain, and undergoes significant elongation in several taxa. Further, while the semicircular canals covary as an integrated module, the utriculus and sacculus of the inner ear instead vary independently of each other. The functional and phylogenetic implications of our findings are discussed.

4: Before trilobite legs: Pygmaclypeatus daziensis reconsidered and the ancestral appendicular organization of Cambrian artiopods
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Posted 19 Aug 2021

Before trilobite legs: Pygmaclypeatus daziensis reconsidered and the ancestral appendicular organization of Cambrian artiopods
146 downloads bioRxiv paleontology

Michel Schmidt, Xianguang Hou, Dayou Zhai, Huijuan Mai, Jelena Belojevic, Xiaohan Chen, Roland R. Melzer, Javier Ortega-Hernandez, Yu Liu

The Cambrian Stage 3 Chengjiang biota in South China is one of the most influential Konservat Lagerstatten worldwide thanks to the fossilization of diverse nonbiomineralizing organisms through pyritization. Despite their contributions to understanding the evolution of early animals, several Chengjiang species remain poorly known due to their scarcity and/or incomplete preservation. Here, we use micro-computed tomography to reveal in detail the ventral appendage organization of the enigmatic non-trilobite artiopod Pygmaclypeatus daziensis, one of the rarest euarthropods in Chengjiang, and explore its functional ecology and broader evolutionary significance. P. daziensis possesses a set of uniramous antennae and 14 pairs of post-antennal biramous appendages, the latter of which show an unexpectedly high degree of heteronomy based on the localized differentiation of the protopodite, endopod and exopod along the antero-posterior body axis. The small body size (less than 2 cm), presence of delicate spinose endites, and well-developed exopods with multiple paddle-shaped lamellae on the appendages of P. daziensis indicate a nekto-benthic mode of life, and a scavenging/detritus feeding strategy. P. daziensis shows that appendage heteronomy is phylogenetically widespread within Artiopoda, the megadiverse clade that includes trilobites and their relatives with nonbiomineralizing exoskeletons and suggests that a single exopod lobe with paddle like lamellae is ancestral for this clade.

5: High lineage survivorship across the end-Devonian Mass Extinction suggested by a remarkable new Late Devonian actinopterygian
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Posted 03 Sep 2021

High lineage survivorship across the end-Devonian Mass Extinction suggested by a remarkable new Late Devonian actinopterygian
138 downloads bioRxiv paleontology

Sam Giles, Kara Feilich, Stephanie E Pierce, Matt Friedman

Actinopterygian (ray-finned) fishes represent the principal vertebrate group in aquatic settings. This dominance is often attributed to their apparent success in the aftermath of the end-Devonian extinction. Increases in taxonomic and morphological diversity in the early Carboniferous, coupled with phylogenetic hypotheses implying the survival of few Devonian lineages, contribute to a model of explosive post-extinction radiation. However, most actinopterygian fossils from within a ca. 20 Myr window surrounding the end-Devonian extinction remain poorly known, contributing to uncertainty about these patterns. Here we present detailed anatomical data for an exceptionally preserved but diminutive ray-finned fish from within this gap, ~7 Myr prior to the Devonian-Carboniferous boundary. Representing a new genus and species, it bears a series of derived anatomical features otherwise known only from Carboniferous and younger taxa. It nests phylogenetically within a clade of post-Devonian species and, in an expanded phylogenetic analysis incorporating other previously neglected taxa, draws at least ten lineages of Carboniferous actinopterygians into the Late Devonian. This suggests phenotypically cryptic divergence among ray-finned fishes in the latest Devonian, followed by more conspicuous diversification in feeding and locomotor structures in the Carboniferous. This revised model finds parallels in patterns emerging for other clades, and provides a refined perspective on key events early in the history of a group that today contains half of all living vertebrate species.

6: Population modelling insights of extinct environments: the case of the Kem Kem palaeocommunity
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Posted 09 Sep 2021

Population modelling insights of extinct environments: the case of the Kem Kem palaeocommunity
133 downloads bioRxiv paleontology

Lucas dos Anjos

The Kem Kem beds are well-known palaeontological deposits. Among the species that lived there, there are some large theropods, such as Deltadromeus agilis, Carcharodontosaurus saharicus, and Spinosaurus aegyptiacus. It is possible that these large predators were facultative scavengers, and they could compete for carrion. In the present paper, I simulate a small community module of this environment, consisting of Carrion, Fishes, Spinosaurus, and a functional group composed of large terrestrial Theropods. I assume that these top predators feed on carrion, but they also have exclusive food sources. I show that these exclusive food sources could have assured the possibility of coexistence, and in their absence, one top predator could be locally extinct.

7: Three new Cenomanian conifers from El Chango (Chiapas, Mexico) offer a snapshot of the geographic mosaic of the Mesozoic conifer decline
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Posted 03 Sep 2021

Three new Cenomanian conifers from El Chango (Chiapas, Mexico) offer a snapshot of the geographic mosaic of the Mesozoic conifer decline
109 downloads bioRxiv paleontology

Ixchel Gonzalez-Ramirez, Sergio RS Cevallos-Ferriz, Carl Rothfels

Premise of study: El Chango is a recently discovered quarry that contains extremely well preserved fossils. The Cenomanian age of the locality corresponds to a time when the global flora was transitioning from gymnosperm- to angiosperm-dominated, yet conifers predominate in this locality. These fossils thus provide a rare opportunity to understand the replacement of conifers by angiosperms as the dominant group of plants. Methods: We collected material from El Chango in annual expeditions (2010 to 2014). We selected the three most abundant and best preserved conifer morphotypes and conducted a total-evidence (i.e., including molecular and morphological data) phylogenetic analysis of a sample of 72 extant conifer species plus the three fossils. We use these results to inform our taxonomic decisions. Results: We obtained four equally most-parsimonious trees (consistency index = 44.1%, retention index = 78.8%). Despite ambiguous relationships among some extant taxa, the three fossil conifers had the same phylogenetic position in all four most parsimonious trees; we describe these species as new: Sequoiadendron helicalancifolium sp. nov. (Cupressaceae), and Microcachrys rhomboidea sp. nov. and Dacrydium bifoliosus sp. nov (Podocarpaceae). The ecosystem is interpreted as a coastal humid mixed forest. Conclusions: Our findings contribute to the understanding of Cenomanian equatorialregions, and support the hypothesis of a geographically and ecologically structured rise of angiosperms, with conifers remaining dominant in brackish-water and angiosperms becoming dominant in freshwater-ecosystems. These fossils fill in gaps in the evolutionary history of lineages like Microcachrys, which we demonstrate occurred in the Northern hemisphere before becoming restricted to its current range (Tasmania).

8: Diverse genetic origins of medieval steppe nomad conquerors
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Posted 16 Dec 2019

Diverse genetic origins of medieval steppe nomad conquerors
104 downloads bioRxiv paleontology

Alexander S. Mikheyev, Lijun Qiu, Alexei Zarubin, Nikita Moshkov, Yuri Orlov, Duane R. Chartier, Igor V. Kornienko, Tatyana G. Faleeva, Vladimir Klyuchnikov, Elena F. Batieva, Tatiana V. Tatarinova

Over millennia, steppe nomadic tribes raided and sometimes overran settled Eurasian civilizations. Most polities formed by steppe nomads were ephemeral, making it difficult to ascertain their genetic roots or what present-day populations, if any, have descended from them. Exceptionally, the Khazar Khaganate controlled the trade artery between the Black and Caspian Seas in VIII-IX centuries, acting as one of the major conduits between East and West. However, the genetic identity of the ruling elite within the polyglot and polyethnic Khaganate has been a much-debated mystery; a controversial hypothesis posits that post-conversion to Judaism the Khazars gave rise to modern Ashkenazim. We analyzed whole-genome sequences of eight men and one woman buried within the distinctive kurgans of the Khazar upper (warrior) class. After comparing them with reference panels of present-day Eurasian and Iron Age populations, we found that the Khazar political organization relied on a polyethnic elite. It was predominantly descended from Central Asian tribes but incorporated genetic admixture from populations conquered by Khazars. Thus, the Khazar ruling class was likely relatively small and able to maintain a genetic identity distinct from their subjugated populations over the course of centuries. Yet, men of mixed ancestry could also rise into the warrior class, possibly providing troop numbers necessary to maintain control of their large territory. However, when the Khaganate collapsed it left few persistent genetic traces in Europe. Our data confirm the Turkic roots of the Khazars, but also highlight their ethnic diversity and some integration of conquered populations.

9: Presenting the Compendium Isotoporum Medii Aevi (CIMA) and Bayesian Case Studies
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Posted 06 Aug 2021

Presenting the Compendium Isotoporum Medii Aevi (CIMA) and Bayesian Case Studies
95 downloads bioRxiv paleontology

Carlo Cocozza, Enrico Cirelli, Marcus Gross, Wolf-Ruediger Teegen, Ricardo Fernandes

The Compendium Isotoporum Medii Aevi (CIMA) gathers more than 50 000 isotopic measurements for bioarchaeological samples located within Europe and its margins dating between AD 500-1500. This volume of isotopic data, together with collected supporting information, offers multiple research opportunities. This is illustrated here using novel Bayesian modelling methods on selected case studies to reconstruct medieval human lifeways (i.e. human subsistence, spatial mobility), animal management practices, and paleo-environmental conditions. We also discuss how the integration of isotopic data with other types of archaeological and historical data can improve our knowledge of historical developments throughout medieval Europe.

10: Does time matter in phylogeny? A perspective from the fossil record
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Posted 11 Jun 2021

Does time matter in phylogeny? A perspective from the fossil record
92 downloads bioRxiv paleontology

Pauline Guenser, Rachel C. M. Warnock, Walker Pett, Philip Donoghue, Emilia Jarochowska

The role of time (i.e. taxa ages) in phylogeny has been a source of intense debate within palaeontology for decades and has not yet been resolved fully. The fossilised birth-death range process is a model that explicitly accounts for information about species through time. It presents a fresh opportunity to examine the role of stratigraphic data in phylogenetic inference of fossil taxa. Here, we apply this model in a Bayesian framework to an exemplar dataset of well-dated conodonts from the Late Devonian. We compare the results to those obtained using traditional unconstrained tree inference. We show that the combined analysis of morphology and stratigraphic data under the FBD range process reduces overall phylogenetic uncertainty, compared to unconstrained tree inference. We find that previous phylogenetic hypotheses based on parsimony and stratophenetics are closer to trees generated under the FBD range process. However, the results also highlight that irrespective of the inclusion of age data, a large amount of topological uncertainty will remain. Bayesian inference provides the most intuitive way to represent the uncertainty inherent in fossil datasets and new flexible models increase opportunities to refine hypotheses in palaeobiology.

11: Comments on a small sabretooth cat in the Abismo Ponta de Flecha Cave, Vale do Ribeira, southeastern Brazil
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Posted 06 Sep 2021

Comments on a small sabretooth cat in the Abismo Ponta de Flecha Cave, Vale do Ribeira, southeastern Brazil
90 downloads bioRxiv paleontology

Artur Chahud

The Vale do Ribeira, located in southeastern Brazil, is known for many caves with osteological material, including several extinct species. The saber-tooth cat Smilodon populator was a large predator that inhabited the Pleistocene and Holocene of South America. A specimen found in the Abismo Ponta de Flecha Cave based on small bones (metacarpals and phalanges) is commented here. The metacarpals have morphological characteristics of S. populator, but are smaller than that of S. fatalis and Panthera onca and larger than that of S. gracilis. The specimen is among the smallest ever found and is comparable in size to an adult lion.

12: New opabiniid diversifies the weirdest wonders of the euarthropod lower stem group
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Posted 11 Mar 2021

New opabiniid diversifies the weirdest wonders of the euarthropod lower stem group
88 downloads bioRxiv paleontology

Stephen Pates, Joanna M Wolfe, Rudy Lerosey-Aubril, Allison C Daley, Javier Ortega-Hernandez

Once considered "weird wonders" of the Cambrian, the emblematic Burgess Shale animals Anomalocaris and Opabinia are now recognized as lower stem-group euarthropods. Anomalocaris and its relatives (radiodonts) had a worldwide distribution and survived until at least the Devonian, whereas - despite intense study - Opabinia remains the only formally described opabiniid to date. Here we reinterpret a fossil from the Wheeler Formation of Utah as a new opabiniid, KUMIP 314087. By visualizing the sample of phylogenetic topologies in treespace, our results fortify support for the position of KUMIP 314087 beyond the nodal support traditionally applied. Our phylogenetic evidence expands opabiniids to multiple Cambrian Stages spanning approximately five million years. Our results underscore the power of treespace visualization for resolving imperfectly preserved fossils and expanding the known diversity and spatiotemporal ranges within the euarthropod lower stem group.

13: A fossil fish assemblage from the middle Miocene of the Cocinetas Basin, northern Colombia
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Posted 20 Apr 2021

A fossil fish assemblage from the middle Miocene of the Cocinetas Basin, northern Colombia
83 downloads bioRxiv paleontology

Gustavo A. Ballen, Carlos Jaramillo, Fernando C. P. Dagosta, Mario C. C. de Pinna

Freshwater fossil fish faunas have been long used to infer past drainage connections, as they are bounded by physical freshwater barriers. Here we study a middle Miocene (15.0--15.5 Ma) fossil fauna (Makaraipao) from the Castilletes Formation in northern Colombia, nowadays west of the Andes. We record the presence of lungfishes (Lepidosiren), pacus (Mylossoma and Piaractus), armored catfishes (Callichthyidae), and red-tail catfishes (Phractocephalus). Extant members of all those groups (except the Callichthyidae, due to lack of taxonomic resolution) are found in Amazonian faunas east of the Andes and are absent from faunas west of the Andes, indicating that the riverine systems of the Guajira Peninsula were connected to Amazonia during the middle Miocene. The similarity of La Venta (west of the Andes) and Rio Acre (east of the Andes) fish faunas during the late Miocene further indicates that the northern Andean uplift was not a complete barrier at least until ~ 11 Myr ago. However, there is a continental-wide structuring of the Miocene fish faunas that is also found in the extant faunas, suggesting that other factors, in addition to the uplift of the Andes, have shaped the biogeographic evolution of South American fish faunas.

14: Generating and testing hypotheses about the fossil record of insect herbivory with a theoretical ecospace
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Posted 16 Jul 2021

Generating and testing hypotheses about the fossil record of insect herbivory with a theoretical ecospace
83 downloads bioRxiv paleontology

Sandra R Schachat, Jonathan L Payne, C. Kevin Boyce, Conrad C Labandeira

A typical fossil flora examined for insect herbivory contains a few hundred leaves and a dozen or two insect damage types. Paleontologists employ a wide variety of metrics to assess differences in herbivory among assemblages: damage type diversity, intensity (the proportion of leaves, or of leaf surface area, with insect damage), the evenness of diversity, and comparisons of the evenness and diversity of the flora to the evenness and diversity of damage types. Although the number of metrics calculated is quite large, given the amount of data that is usually available, the study of insect herbivory in the fossil record still lacks a quantitative framework that can be used to distinguish among different causes of increased insect herbivory and to generate null hypotheses of the magnitude of changes in insect herbivory over time. Moreover, estimates of damage type diversity, the most common metric, are generated with inconsistent sampling standardization routines. Here we demonstrate that coverage-based rarefaction yields valid and reliable estimates of damage type diversity that are robust to differences among floral assemblages in the number of leaves examined, average leaf surface area, and the inclusion of plant organs other than leaves such as seeds and axes. We outline the potential of a theoretical ecospace that combines various metrics to distinguish between potential causes of increased herbivory. We close with a discussion of the most appropriate uses of a theoretical ecospace for insect herbivory, with the overlapping damage type diversities of Paleozoic gymnosperms and Cenozoic angiosperms as a brief case study.

15: Computed tomography reveals hip dysplasiain the extinct Pleistocene saber-tooth cat Smilodon
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Posted 07 Jan 2020

Computed tomography reveals hip dysplasiain the extinct Pleistocene saber-tooth cat Smilodon
83 downloads bioRxiv paleontology

Mairin A Balisi, Abhinav K Sharma, Carrie M Howard, Christopher A Shaw, Robert Klapper, Emily L Lindsey

Reconstructing the behavior of extinct species is challenging, particularly for those with no living analogues. However, damage preserved as paleopathologies on bone can record how an animal moved in life, potentially reflecting behavioral patterns. Here, we assess hypothesized etiologies of pathology in a pelvis and associated right femur of a Smilodon fatalis saber-toothed cat, one of the best-studied species from the Pleistocene-age Rancho La Brea asphalt seeps, California, USA, using visualization by computed tomography (CT). The pelvis exhibits massive destruction of the right hip socket that was interpreted, for nearly a century, to have developed from trauma and infection. CT imaging reveals instead that the pathological distortions characterize chronic remodeling that began at birth and led to degeneration of the joint over the animal's life. These results suggest that this individual suffered from hip dysplasia, a congenital condition common in domestic dogs and cats. This individual reached adulthood but could not have hunted properly nor defended territory on its own, likely relying on a social group for feeding and protection. While extant social felids are rare, these fossils and others with similar pathologies are consistent with a spectrum of social strategies in Smilodon supported by a predominance of previous studies.

16: Online spike sorting via deep contractive autoencoder
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Posted 24 Apr 2021

Online spike sorting via deep contractive autoencoder
82 downloads bioRxiv paleontology

Morteza Moazami Goudarzi, Mohammadreza Radmanesh, Ahmad Asgharian Rezaei, Alireza Hashemi, Mahdi Jalili

Spike sorting-the process of separating spikes from different neurons-is often the first and most critical step in the neural data analysis pipeline. Spike-sorting techniques isolate a single neuron's activity from background electrical noise based on the shapes of the waveforms (WFs) obtained from extracellular recordings. Despite several advancements in this area, an important remaining challenge in neuroscience is online spike sorting, which has the potential to significantly advance basic neuroscience research and the clinical setting by providing the means to produce real-time perturbations of neurons via closed-loop control. Current approaches to online spike sorting are not fully automated, are computationally expensive and are often outperformed by offline approaches. In this paper, we present a novel algorithm for fast and robust online classification of single neuron activity. This algorithm is based on a deep contractive autoencoder (DCAE) architecture. DCAEs are deep neural networks that can learn a latent state representation of their inputs. The main advantage of DCAE approaches is that they are less sensitive to noise (i.e., small perturbations in their inputs). We therefore reasoned that they can form the basis for robust online spike sorting algorithms. Overall, our DCAE-based online spike sorting algorithm achieves over 90% accuracy at sorting previously-unseen spike waveforms. Moreover, our approach produces superior results compared to several state-of-the-art offline spike-sorting procedures.

17: Late Anisian microbe-metazoan build-ups ('stromatolites') in the Germanic Basin -- aftermath of the Permian -- Triassic Crisis
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Posted 16 Mar 2021

Late Anisian microbe-metazoan build-ups ('stromatolites') in the Germanic Basin -- aftermath of the Permian -- Triassic Crisis
80 downloads bioRxiv paleontology

Yu Pei, Jan-peter Duda, Jan Schoenig, Cui Luo, Joachim Reitner

The so-called Permian -- Triassic mass extinction was followed by a prolonged period of ecological recovery that lasted until the Middle Triassic. Triassic stromatolites from the Germanic Basin seem to be an important part of the puzzle, but have barely been investigated so far. Here we analyzed late Anisian (upper Middle Muschelkalk) stromatolites from across the Germanic Basin by combining petrographic approaches (optical microscopy, micro X-ray fluorescence, Raman imaging) and geochemical analyses (sedimentary hydrocarbons, stable carbon and oxygen isotopes). Paleontological and sedimentological evidence, such as Placunopsis bivalves, intraclasts and disrupted laminated fabrics, indicate that the stromatolites formed in subtidal, shallow marine settings. This interpretation is consistent with {delta}13Ccarb of about -2.1 % to -0.4 %. Occurrences of calcite pseudomorphs after gypsum suggest slightly evaporitic environments, which is well in line with the relative rarity of fossils in the host strata. Remarkably, the stromatolites are composed of microbes (perhaps cyanobacteria and sulfate reducing bacteria) and metazoans such as non-spicular demosponges, Placunopsis bivalves, and/or Spirobis-like worm tubes. Therefore, these ''stromatolites'' should more correctly be referred to as microbe-metazoan build-ups. They are characterized by diverse lamination types, including planar, wavy, domal and conical ones. Microbial mats likely played an important role in forming the planar and wavy laminations. Domal and conical laminations commonly show clotted to peloidal features and mesh-like fabrics, attributed to fossilized non-spicular demosponges. Our observations not only point up that non-spicular demosponges are easily overlooked and might be mistakenly interpreted as stromatolites, but also demonstrate that microbe-metazoan build-ups were widespread in the Germanic Basin during Early to Middle Triassic times. In the light of our findings, it appears plausible that the involved organisms benefited from elevated salinities. Another (not necessarily contradictory) possibility is that the mutualistic relationship between microbes and non-spicular demosponges enabled these organisms to fill ecological niches cleared by the Permian -- Triassic Crisis. If that is to be the case, it means that such microbe-metazoan associations maintained their advantage until the Middle Triassic.

18: Estimating the age of poorly dated fossil specimens and deposits using a total-evidence approach and the fossilized birth-death process
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Posted 13 Apr 2021

Estimating the age of poorly dated fossil specimens and deposits using a total-evidence approach and the fossilized birth-death process
79 downloads bioRxiv paleontology

Joelle Barido-Sottani, Dagmara Zyla, Tracy A. Heath

Bayesian total-evidence approaches under the fossilized birth-death model enable biologists to combine fossil and extant data---while accounting for uncertainty in the ages of fossil specimens---in an integrative phylogenetic analysis. Fossil age uncertainty is a key feature of the fossil record as many empirical datasets may contain a mix of precisely dated and poorly dated fossil specimens or deposits. In this study, we explore whether reliable age estimates for fossil specimens can be obtained from Bayesian total-evidence phylogenetic analyses under the fossilized birth-death model. Through simulations based on the example of the Baltic amber deposit, we show that estimates of fossil ages obtained through such an analysis are accurate, particularly when the proportion of poorly dated specimens remains low and the majority of fossil specimens have precise dates. We confirm our results using an empirical dataset of living and fossil penguins by artificially increasing the age uncertainty around some fossil specimens and showing that the resulting age estimates overlap with the recorded age ranges. Our results are applicable to many empirical datasets where classical methods of establishing fossil ages have failed, such as the Baltic amber and the Gobi Desert deposits.

19: New fossils of Australopithecus sediba reveal a nearly complete lower back
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Posted 29 May 2021

New fossils of Australopithecus sediba reveal a nearly complete lower back
78 downloads bioRxiv paleontology

Scott A Williams, Thomas Cody Prang, Marc R Meyer, Thierra K Nalley, Renier Van Der Merwe, Christopher Yelverton, Daniel Garcia-Martinez, Gabrielle A Russo, Kelly R Ostrofsky, Jennifer Eyre, Mark Grabowski, Shahed Nalla, Markus Bastir, Peter Schmid, Steven E Churchill, Lee R Berger

Adaptations of the lower back to bipedalism are frequently discussed but infrequently demonstrated in early fossil hominins. Newly discovered lumbar vertebrae contribute to a near-complete lower back of Malapa Hominin 2 (MH2), offering additional insights into posture and locomotion in Australopithecus sediba. We show that MH2 demonstrates a lower back consistent with human-like lumbar lordosis and other adaptations to bipedalism, including an increase in the width of intervertebral articular facets from the upper to lower lumbar column ("pyramidal configuration"). This contrasts with recent work on lordosis in fossil hominins, where MH2 was argued to demonstrate no appreciable lordosis ("hypolordosis") similar to Neandertals. Our three-dimensional geometric morphometric (3D GM) analyses show that MH2s nearly complete middle lumbar vertebra is human-like in shape but bears large, cranially-directed transverse processes, implying powerful trunk musculature. We interpret this combination of features to indicate that A. sediba used its lower back in both human-like bipedalism and ape-like arboreal positional behaviors, as previously suggested based on multiple lines of evidence from other parts of the skeleton and reconstructed paleobiology of A. sediba.

20: New insights into the earlier evolutionary history of epiphytic macrolichens
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Posted 03 Aug 2021

New insights into the earlier evolutionary history of epiphytic macrolichens
77 downloads bioRxiv paleontology

Qiuxia Yang, Yanyan Wang, Robert Lucking, H. Thorsten Lumbsch, Xin Wang, Zhenyong Du, Yunkang Chen, Ming Bai, Dong Ren, Jiangchun Wei, Hu Li, Yongjie Wang, Xinli Wei

Lichens are well known as pioneer organisms colonizing bare surfaces such as rocks and therefore have been hypothesized to play a role in the early formation of terrestrial ecosystems. Given the rarity of fossil evidence, our understanding of the evolutionary history of lichen-forming fungi is primarily based on molecular dating approaches. These studies suggest extant clades of macrolichens diversified after the K-Pg boundary. Here we corroborate the mid-Mesozoic fossil Daohugouthallus ciliiferus as an epiphytic macrolichen that predates the K-Pg boundary by 100 Mys. Based on new material and geometric morphometric analysis, we demonstrate that the Jurassic fossil is morphologically most similar to Parmeliaceae, but cannot be placed in Parmeliaceae or other similar family-level clades forming macrolichens as these evolved much later. Consequently, a new family, Daohugouthallaceae, is proposed here to accommodate this fossil, which reveals macrolichens may have been diverse long before the Cenozoic diversification of extant lineages.

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