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in category paleontology

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

141: Revisiting the phosphorite deposit of Fontanarejo (central Spain): new window into the early Cambrian evolution of sponges and into the microbial origin of phosphorites
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Posted 13 Dec 2020

Revisiting the phosphorite deposit of Fontanarejo (central Spain): new window into the early Cambrian evolution of sponges and into the microbial origin of phosphorites
459 downloads bioRxiv paleontology

Joachim Reitner, Cui Luo, Pablo Suarez-Gonzales, Jan-Peter Duda

Fossils within early Cambrian phosphorites worldwide are often well preserved due to early diagenetic permineralization. Here, we examine the fossil record contained within phosphorites of the Lower Cambrian Pusa Formation (late Fortunian to Cambrian Stage 2) in Fontanarejo, central Spain. The sedimentology and age of these phosphorites have been controversial and are here reviewed and discussed, providing also a updated geological map. The Pusa Formation is composed of fine clastic sediments that are partly turbiditic, with channels of quartz-rich conglomerates and abundant phosphorites in the upper part of the succession. The microfacies and mineralogy of these channel deposits are studied here for the first time in detail, showing that they are mainly composed of subspherical apatite clasts, with minor mudstone intraclasts, quartzite and mica grains. Numerous sponge spicules, as well as entirely preserved hexactinellid sponges and demosponges, were collected within these phosphorites and likely represent stem groups. In addition to sponges, other fossils, such as small shelly fossils (SSF) of the mollusk Anabarella sp., were found. The phosphorites exhibit multiple evidence of intense microbial activity, including diverse fabrics (phosphatic oncoidal-like microbialites, thrombolites, stromatolites, and cements) and abundant fossils of filamentous microbes that strongly resemble sulfur oxidizing bacteria. Our findings strongly suggest that microbial processes mediated the rapid formation of most of the Fontanarejo apatite, probably accounting for the exceptional preservation of fragile fossils such as sponge skeletons. The apparent presence of taxonomically diverse hexactinellid and demosponge communities by the lowermost Cambrian further corroborates a Precambrian origin of the phylum Porifera

142: 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
458 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.

143: Reversing Time Averaging and Reconstructing Extinction Rates with Approaches from Image Processing
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Posted 05 Sep 2018

Reversing Time Averaging and Reconstructing Extinction Rates with Approaches from Image Processing
446 downloads bioRxiv paleontology

Niklas Hohmann

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

144: Surface sediment samples from early age of seafloor exploration can provide a late 19th century baseline of the marine environment
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Posted 18 Sep 2018

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

Marina C. Rillo, Michal Kucera, Thomas H. G. Ezard, C. Giles Miller

Historical seafloor samples collected up to 150 years ago represent an important archive to benchmark the extent of current ocean acidification and pollution trends. Such benchmarking requires that the historical sediment samples represent the state of the environment at- or shortly before the time of collection. However, early oceanographic expeditions sampled the ocean floor using devices like the sounding tube or a dredge, which potentially disturb the sediment surface and recover a mix of Holocene (surface) and Pleistocene sediments. Here we use climate-sensitive microfossils as a fast and efficient biometric method to assess to what degree historical seafloor samples contain a mixture of modern and glacial sediments. Our assessment is based on comparing the composition of planktonic foraminifera (PF) assemblages in historical samples with Holocene and Last Glacial Maximum (LGM) global reference datasets. We show that eight out of the nine historical samples contain PF assemblages more similar to the Holocene than to the LGM PF assemblages. This result suggests that the majority of sediment samples from historical collections should be suitable to provide baseline of the state of marine ecosystems in the late 19th century.

145: 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
431 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.

146: The oldest peracarid crustacean reveals a Late Devonian freshwater colonisation by isopod relatives
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Posted 26 Apr 2021

The oldest peracarid crustacean reveals a Late Devonian freshwater colonisation by isopod relatives
421 downloads bioRxiv paleontology

Ninon Robin, Pierre Gueriau, Javier Luque, David Jarvis, Allison Daley, Ronald Vonk

Peracarida (e.g., woodlice & side-swimmers) are, together with their sister-group Eucarida (e.g. krill & decapods), the most speciose group of modern crustaceans, suggested to have appeared as early as the Ordovician. While eucarids incursion onto land consists of mainly freshwater and littoral grounds, some peracarids have evolved fully terrestrial ground-crawling ecologies, inhabiting even our gardens in temperate regions (e.g. pillbugs and sowbugs). Their fossil record extends back to the Carboniferous and consists mainly of marine occurrences. Here, we provide a complete re-analysis of a fossil arthropod, Oxyuropoda, reported in 1908 from the Late Devonian floodplains of Ireland, and left with unresolved systematic affinities despite a century of attempts at identification. Known from a single specimen preserved in two-dimensions, we analysed its anatomy using digital microscopy and multispectral macro-imaging to enhance contrast of morphological structures. The new anatomical characters and completeness of Oxyuropoda, together with a phylogenetic analysis with representatives of all major Eumalacostraca groups, indicate that Oxyuropoda is a crown-peracarid, part of a clade including amphipods and isopods. As such, Oxyuropoda is the oldest known Peracarida, and provides evidence that derived peracarids had an incursion into freshwater and terrestrial environments as early as the Famennian, more than 360 million years ago.

147: Rhizoliths identified as prehistoric filing tools for fishhook production on San Nicolas Island, California
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Posted 07 Jan 2021

Rhizoliths identified as prehistoric filing tools for fishhook production on San Nicolas Island, California
420 downloads bioRxiv paleontology

Sebastian K.T.S. Wärmländer, Kevin N. Smith, René L. Vellanoweth, Ryan Moritz, Kjell Jansson, Tim Gooding, William E. Kendig, Sabrina B. Sholts

Chemical analysis of archeological objects can provide important clues about their purpose and function. In this study, we used scanning electron microscopy (SEM) and chemical spectroscopy (SEM-EDS and XRD) to identify a white residue present on cylindrical rhizoliths from a component at an archaeological site (CA-SNI-25) on San Nicolas Island, California, dated ca. AD 1300 to 1700. The residue was found to consist of biogenic calcite and aragonite particles, different in composition and morphology from the CaCO3 particles in the rhizoliths, but identical to marine shell material. These results, together with observations of surface micro-wear patterning on fishhooks and rhizoliths, replicative experiments, in situ spatial analysis, and other archaeological evidence, show that rhizoliths were used as files in a larger tool kit for crafting shell fishhooks. Our findings shed new light on the technological innovations devised by Native Americans to exploit the rich marine resources surrounding the Channel Islands, and provide the first analytical evidence for the use of rhizoliths as a production tool.

148: Millennial-scale change on a Caribbean reef system that experiences hypoxia
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Posted 08 Apr 2021

Millennial-scale change on a Caribbean reef system that experiences hypoxia
415 downloads bioRxiv paleontology

Blanca Figuerola, Ethan L Grossman, Noelle Lucey, Nicole D Leonard, Aaron O'Dea

Coastal hypoxia has become an increasingly acknowledged threat to coral reefs that is potentially intensifying because of increased input of anthropogenic nutrients. Almirante Bay (Caribbean Panama) is a semi-enclosed system that experiences hypoxia in deeper waters which occasionally expand into shallow coral reefs, suffocating most aerobic benthic life. To explore the long-term history of reefs in the bay we extracted reef matrix cores from two reefs that today experience contrasting patterns of oxygenation. We constructed a 1800-year-long record of gastropod assemblages and isotope compositions from six U-Th chronologically-constrained reef matrix cores. We extracted two cores from each reef at 3 m water depth and two additional cores from a deeper part (4.8 m) of the hypoxia-exposed reef. Results show that the deeper part of the hypoxic reef slowed in growth and stopped accreting approximately 1500 years BP while the shallow part of the reef continued to accrete to the present day, in agreement with a model of expanding hypoxia at this time. Our proxy-based approach suggests that differences among these palaeoindicators in the two reefs may have been driven by an increase in hypoxia via eutrophication caused by either natural changes or human impacts. Similar patterns of increasing herbivores and decreasing carbon isotope values occurred in the shallow part of the hypoxic reef during the last few decades. This suggests that hypoxia may be expanding to depths as shallow as 3 m and that shallow reefs are experiencing greater risk due to increased human activity.

149: 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
412 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.

150: Differential taphonomic effects of petroleum seeps and karstic sinkholes on ancient dire wolf teeth: Hydrocarbon impregnation preserves fossils for chemical and histological analysis
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Posted 05 Jan 2021

Differential taphonomic effects of petroleum seeps and karstic sinkholes on ancient dire wolf teeth: Hydrocarbon impregnation preserves fossils for chemical and histological analysis
406 downloads bioRxiv paleontology

Sabrina B. Sholts, Leslea J. Hlusko, Joshua P. Carlson, Sebastian K. T. S. Wärmländer

Histological analysis of teeth can yield information on an organisms growth and development, facilitating investigations of diet, health, environment, and long-term responses to selective pressures. In the Americas, an extraordinary abundance of Late Pleistocene fossils including teeth has been preserved in petroleum seeps, constituting a major source of information about biotic changes and adaptations at the end of the last glacial period. However, the usefulness of these fossils for histological studies is unclear, due to the unknown taphonomic effects of long-term deposition in petroleum. Here, we compare histological and chemical analyses on dire wolf (Canis dirus) teeth obtained from two different environments, i.e. a petroleum seep (Rancho La Brea tar pits, California) and a carstic sinkhole (Cutler Hammock sinkhole, Florida). Optical and scanning electron microscopy (SEM) together with X-ray diffraction (XRD) analysis revealed excellent preservation of dental microstructure in the seep sample, and the petroleum-induced discoloration was found not to interfere with the histological and chemical examination. By comparison, teeth from the sinkhole sample showed severe degradation and contamination of the dentine by exogenous substances. These results indicate that petroleum seep assemblages are useful, or even ideal, environments for preserving the integrity of fossil material for chemical and histological analysis.

151: The measurement of species selection on evolving characters
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Posted 15 Aug 2017

The measurement of species selection on evolving characters
400 downloads bioRxiv paleontology

Carl Simpson

Many processes can contribute to macroevolutionary change. This fact is the source of the wide variety of macroevolutionary change across time and taxa as well as the bane of paleobiological research trying to understand how macroevolution works. Here, I present a general framework for understanding the variety of macroevolutionary phenomena. Based on Price's theorem, this framework provides a simple quantitative means to understand (1) the macroevolutionary processes that are possible and (2) the way those processes interact with each other. The major qualitative features of macroevolution depend first on the number of processes that co-occur and then on the magnitudes and evolutionary directions of those processes. Species selection, the major macroevolutionary process, consists of patterns of differential rates of speciation and extinction. Its macroevolutionary efficacy depends on the presences of sufficient microevolutionary change. Conversely, microevolutionary change is limited in power by the independent evolution of species, and species selection acting across populations of species can amplify or suppress microevolution. Non-trends may result if species selection sufficiently neutralizes microevolution and may yield stable macroevolutionary patterns over many millions of years.

152: Terrestrial effects of moderately nearby supernovae
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Posted 08 Dec 2017

Terrestrial effects of moderately nearby supernovae
396 downloads bioRxiv paleontology

Adrian L. Melott, Brian C Thomas

Recent data indicate one or more moderately nearby supernovae in the early Pleistocene, with additional events likely in the Miocene. This has motivated more detailed computations, using new information about the nature of supernovae and the distances of these events to describe in more detail the sorts of effects that are indicated at the Earth. This short communication/review is designed to describe some of these effects so that they may possibly be related to changes in the biota around these times.

153: Modern botanical analogue of endangered Yak (Bos mutus) dung from India: Plausible linkage with living and extinct megaherbivores
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Posted 09 Aug 2018

Modern botanical analogue of endangered Yak (Bos mutus) dung from India: Plausible linkage with living and extinct megaherbivores
396 downloads bioRxiv paleontology

Sadhan K. Basumatary, Hukam Singh, H. Gregory McDonald, Swati Tripathi, Anil K. Pokharia

The study present to document the micro and macrobotanical remain on wild Yak dung to understand the diet, habitat, and ecology in relation to determining possible ecological relationships with extant and extinct megaherbivores. Grasses are the primary diet of the yak as indicated by the abundance of grass pollen and phytoliths, though it is obvious. The other associates non-arboreal and arboreal taxa namely, Cyperacaeae, Rosaceae, Chenopodiaceae, Artemisia, Prunus, and Rhododendron are also important dietary plants for their survival. The observation of plant macrobotanical remains especially the vegetative part and seed of the grasses and Cyperaceae also indicates good agreement with the palynodata. The documented micro and macrobotanical data is indicative of both Alpine meadow and steppe vegetation under cold and dry climate which exactly reflected the current vegetation composition and climate in the region. The recovery of Botryococcus, Arcella, and diatom was marked though in trace values and suggestive of the perennial water system in the region which incorporated through the ingestion of water. Energy dispersive spectroscopy analysis marked that the element contained in dung samples has variation in relation to the summer and winter which might be the availability of the food plants and vegetation. This generated multiproxy data serves as a strong supplementary data for modern pollen and vegetation relationship based on surface soil samples in the region. The recorded multiproxy data could be useful to interpret the coprolites of herbivorous fauna in relation to the palaeodietary and paleoecology in the region and to correlate with other mega herbivores in a global context.

154: Sedimentary factories and ecosystem change across the Permian-Triassic Critical Interval (P-TrCI) – insights from the Xiakou area (South China)
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Posted 10 Aug 2020

Sedimentary factories and ecosystem change across the Permian-Triassic Critical Interval (P-TrCI) – insights from the Xiakou area (South China)
390 downloads bioRxiv paleontology

Yu Pei, Jan-Peter Duda, Joachim Reitner

The Permian-Triassic mass extinction included a potentially catastrophic decline of biodiversity, but ecosystem change across this event remains poorly characterized. Here we reconstruct sedimentary factories and ecosystem change across the Permian-Triassic Critical Interval (P-TrCI) in the Xiakou area (South China). Six microfacies (MF) were classified. The succession begins with a eukaryote-controlled carbonate factory (MF-1) that passes upward into an organomineralization-dominated carbonate factory (MF-2–3). Organic-rich marls atop these units reflect carbonate factory collapse (MF-4). Organomineralization-driven carbonate formation restarts prior to the Permian-Triassic boundary (MF-5) and subsequently develops into a mixed carbonate factory where organomineralization and biomineralization are almost equally important (MF-6). MF-1 reflects oxygenated shallow water environments. In contrast, MF-2–6 were all deposited in somewhat deeper environments, some of which episodically exhibited elevated salinities, oxygen depletion, and, possibly, euxinic conditions. Our results demonstrate that distinct changes in carbonate production styles, biodiversity, and environmental conditions are not synchronous at Xiakou. Furthermore, the Xiakou record is strikingly different to that of other localities, even from the same area (e.g., the Global Stratotype Section and Point section at Meishan). Together, these findings highlight the enormous complexity of the P-TrCI and calls simplified views of the Permian-Triassic mass extinction into question. ### Competing Interest Statement The authors have declared no competing interest.

155: Bioarchaeological sex prediction from central Italy using generalized low rank imputation for cross-validated metric craniodental supervised ensemble machine learning with missing data
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Posted 05 Nov 2020

Bioarchaeological sex prediction from central Italy using generalized low rank imputation for cross-validated metric craniodental supervised ensemble machine learning with missing data
378 downloads bioRxiv paleontology

Evan Muzzall

I use a novel supervised ensemble machine learning approach to verify sex estimation of archaeological skeletons from central Italian bioarchaeological contexts with large amounts of missing data present. Eighteen cranial interlandmark distances and five maxillary metric distances were recorded from n = 240 estimated males and n = 180 estimated females from four locations at Alfedena (600-400 BCE) and two locations at Campovalano (750-200 BCE and 9-11th Century CE). A generalized low rank model (GLRM) was used to impute missing data and 20-fold external stratified cross-validation was used to fit an ensemble of eight machine learning algorithms to six different subsets of the data: 1) the face, 2) vault, 3) cranial base, 4) combined face/vault/base, 5) dentition, and 6) combined cranianiodental. Area under the receiver operator characteristic curve (AUC) was used to evaluate the predictive performance of six constituent algorithms, the discrete algorithmic winner(s), and the SuperLearner weighted ensemble's classification of males and females from these six bony regions. This approach is useful for predicting male/female sex from central Italy. AUC for the combined craniodental data was the highest (0.9722), followed by the combined cranial data (0.9644), the face (0.9426), vault (0.9116), base (0.9060), and dentition (0.7421). Cross-validated ensemble machine learning of cranial and dental data shows strong potential for estimating sex in the bioarchaeological record and can contribute additional perspectives to help refine our understanding of human sex estimation. Additionally, GLRMs have the potential to handle missing data in ways previously unexplored in the discipline. The main limitation is that the biological sexes of the individuals estimated in this study are not certain, but were estimated macroscopically using common bioarchaeological methods. However, these methods show great promise for estimation of sex in bioarchaeological and forensic contexts and should be investigated on known-sex reference samples for confirmation. ### Competing Interest Statement The authors have declared no competing interest.

156: Holocephali From the Irati Formation (Paraná Basin), Brazil: Origin, Paleogographical and Paleoenvironmental Considerations
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Posted 10 Oct 2020

Holocephali From the Irati Formation (Paraná Basin), Brazil: Origin, Paleogographical and Paleoenvironmental Considerations
370 downloads bioRxiv paleontology

Artur Chahud

The Permian (Cisuralian) Irati Formation, from the Brazilian southeastern Parana Basin bears, at some levels, Chondrichthyes, besides other vertebrates. Outcrops of this unit are frequent at the state of Sao Paulo eastern belt. Two members of the Irati are recognized at this state, Assistencia, the upper, and Taquaral. A sandy facies, mostly at the base of the Taquaral, is noteworthy by the richness of the Chondrichthyes, mainly Holocephali. The Petalodontiformes are the Chondrichthyes most abundant, so far referred to Itapyrodus punctatus. Recent studies of several specimens revealed that some morphotypes must belong to different species of the genus Itapyrodus. Others are akin to this genus, justifying a proposition of an endemic family Itapyrodidae. The presence of this endemic family is an argument, among others, for a proposed isolation of two Brazilan Basins northeast Parnaiba and southeast Parana, during the time of deposition of the Irati, inasmuch as Itapyrodidae are present in both basins. ### Competing Interest Statement The authors have declared no competing interest.

157: Muon Radiation Dose and Marine Megafaunal Extinction at the end-Pliocene Supernova
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Posted 28 Dec 2017

Muon Radiation Dose and Marine Megafaunal Extinction at the end-Pliocene Supernova
364 downloads bioRxiv paleontology

Adrian L. Melott, Franciole Marinho, Laura Paulucci

Considerable data and analysis support the detection of a supernova at a distance of about 50 pc, ~2.6 million years ago. This is possibly related to the extinction event around that time and is a member of a series of explosions which formed the Local Bubble in the interstellar medium. We build on the assumptions made in previous work, and propagate the muon flux from supernova-initiated cosmic rays from the surface to the depths of the ocean. We find that the radiation dose from the muons will exceed the total present surface dose from all sources at depths up to a kilometer and will persist for at least the lifetime of marine megafauna. It is reasonable to hypothesize that this increase in radiation load may have contributed to a newly documented marine megafaunal extinction at that time.

158: Metacommunity analyses show increase in ecological specialisation throughout the Ediacaran
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Posted 17 May 2021

Metacommunity analyses show increase in ecological specialisation throughout the Ediacaran
348 downloads bioRxiv paleontology

Rebecca Eden, Andrea Manica, Emily G. Mitchell

The first animals appear during the late Ediacaran (572 - 541 Ma); an initial diversity increase was followed by a drop, interpreted as catastrophic mass extinction. We investigate the processes underlying these changes using the "Elements of Metacommunity Structure" framework. The oldest metacommunity was characterized by taxa with wide environmental tolerances, and limited specialisation and inter-taxa interactions. Structuring increased in the middle metacommunity, with groups of taxa sharing synchronous responses to environmental gradients, aggregating into distinct communities. This pattern strengthened in the youngest metacommunity, with communities showing strong environmental segregation and depth structure. Thus, metacommunity structure increased in complexity, with increased specialisation and resulting competitive exclusion, not a catastrophic environmental disaster, leading to diversity loss in the terminal Ediacaran, revealing that the complex eco-evolutionary dynamics associated with Cambrian diversification were established in the Ediacaran.

159: Foot scales in the Early Cretaceous bird Gansus yumenensis from China
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Posted 08 Jun 2021

Foot scales in the Early Cretaceous bird Gansus yumenensis from China
347 downloads bioRxiv paleontology

Tao Zhao, Zhiheng LI, He Zhang, Yanhong Pan

Most modern birds have scales covering the foot and feathers elsewhere. Discoveries of fossil feathers attached to the metatarsus in non-avian dinosaurs and basal birds suggests that the avian scales are secondarily derived from feathers. However, our knowledge of early avian scales and their taphonomy is still limited, due to the scarcity of fossil record. Here we employ multiple techniques to characterize the morphological and chemical details preserved and investigate how they are preserved in the skin of IVPP V15077, a referred specimen of the Early Cretaceous Gansus yumenensis. Results show that two types of scales, scutellate and interstitial scales, are preserved in IVPP V15077, which, in combination with previous discovery of scutate and reticulate scales in other Early Cretaceous birds, indicates that all four types of scales present in modern birds have appeared in the Early Cretaceous. SEM observations and Raman analysis suggest that the skin of Gansus yumenensis may be pigmented. Elemental mapping indicates that aluminosilicates and calcium phosphate are involved in the mineralization of the skin.

160: Preservation of collagen in the soft tissues of frozen mammoths
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Posted 12 Apr 2021

Preservation of collagen in the soft tissues of frozen mammoths
347 downloads bioRxiv paleontology

Shunji Hattori, Tomomi Kiriyama-Tanaka, Masashi Kusubata, Yuki Taga, Testuya Ebihara, Katsuyuki Imai, Mitsutaka Miura, Yoshihiro Mezaki, Alexei Tikhonov, Haruki Senoo

We investigated the characteristics of extracellular matrix (ECM) in the soft tissue of two frozen baby woolly mammoths (Mammuthus primigenius) that died and were buried in Siberian permafrost approximately 40,000 years ago. Morphological and biochemical analyses of mammoth lung and liver demonstrated that those soft tissues were preserved at the gross anatomical and histological levels. The ultrastructure of ECM components, namely a fibrillar structure with a collagen-characteristic pattern of cross-striation, was clearly visible with transmission and scanning electron microscopy. Type I and type IV collagens were detected by immunohistochemical observation. Quantitative amino acid analysis of liver and lung tissues of the baby mammoths indicated that collagenous protein is selectively preserved in these tissues as a main protein. Type I and type III collagens were detected as major components by means of liquid chromatography-mass spectrometry analysis after digestion with trypsin. These results indicate that the triple helical collagen molecule, which is resistant to proteinase digestion, has been preserved in the soft tissues of these frozen mammoths for 40,000 years.

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