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Results 141 through 160 out of 197

in category paleontology

 

141: Late Anisian microbe-metazoan build-ups ('stromatolites') in the Germanic Basin -- aftermath of the Permian -- Triassic Crisis

Yu Pei, Jan-peter Duda et al.

472 downloads (posted 16 Mar 2021)

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.

https://rxivist.org/papers/133530
https://doi.org/10.1101/2021.03.15.435468

142: The balancing act of Nipponites mirabilis (Nostoceratidae, Ammonoidea): managing hydrostatics during a complex ontogenetic trajectory

David J. Peterman, Tomoyuki Mikami et al.

467 downloads (posted 11 Jun 2020)

Nipponites is a heteromorph ammonoid with a complex and unique morphology that obscures its mode of life and ethology. The seemingly aberrant shell of this Late Cretaceous nostoceratid seems deleterious. However, hydrostatic simulations suggest that this morphology confers several advantages for exploiting a quasi-planktic mode of life. Virtual, 3D models of Nipponites mirabilis were used to compute various hydrostatic properties through 14 ontogenetic stages. At each stage, Nipponites had the capacity for neutral buoya...

https://rxivist.org/papers/86990
https://doi.org/10.1101/2020.06.11.145813

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

Joachim Reitner, Cui Luo et al.

466 downloads (posted 13 Dec 2020)

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,...

https://rxivist.org/papers/121418
https://doi.org/10.1101/2020.12.13.422563

144: A fossil fish assemblage from the middle Miocene of the Cocinetas Basin, northern Colombia

Gustavo A. Ballen, Carlos Jaramillo et al.

448 downloads (posted 20 Apr 2021)

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...

https://rxivist.org/papers/138792
https://doi.org/10.1101/2021.04.19.440491

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

Niklas Hohmann

447 downloads (posted 05 Sep 2018)

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 bl...

https://rxivist.org/papers/32194
https://doi.org/10.1101/408864

146: Millennial-scale change on a Caribbean reef system that experiences hypoxia

Blanca Figuerola, Ethan L Grossman et al.

442 downloads (posted 08 Apr 2021)

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 constr...

https://rxivist.org/papers/137001
https://doi.org/10.1101/2021.04.06.438665

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

Marina C. Rillo, Michal Kucera et al.

439 downloads (posted 18 Sep 2018)

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 Plei...

https://rxivist.org/papers/32984
https://doi.org/10.1101/419770

148: The oldest peracarid crustacean reveals a Late Devonian freshwater colonisation by isopod relatives

Ninon Robin, Pierre Gueriau et al.

429 downloads (posted 26 Apr 2021)

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 m...

https://rxivist.org/papers/139602
https://doi.org/10.1101/2021.04.25.441336

149: Rhizoliths identified as prehistoric filing tools for fishhook production on San Nicolas Island, California

Sebastian K.T.S. Wärmländer, Kevin N. Smith et al.

423 downloads (posted 07 Jan 2021)

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 partic...

https://rxivist.org/papers/123789
https://doi.org/10.1101/2021.01.05.425479

150: Estimating the age of poorly dated fossil specimens and deposits using a total-evidence approach and the fossilized birth-death process

Joelle Barido-Sottani, Dagmara Zyla et al.

418 downloads (posted 13 Apr 2021)

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-evi...

https://rxivist.org/papers/137744
https://doi.org/10.1101/2021.04.12.439507

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

Sabrina B. Sholts, Leslea J. Hlusko et al.

417 downloads (posted 05 Jan 2021)

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, du...

https://rxivist.org/papers/123615
https://doi.org/10.1101/2021.01.04.425345

152: The measurement of species selection on evolving characters

Carl Simpson

409 downloads (posted 15 Aug 2017)

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 in...

https://rxivist.org/papers/30125
https://doi.org/10.1101/176438

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

Sadhan K. Basumatary, Hukam Singh et al.

399 downloads (posted 09 Aug 2018)

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...

https://rxivist.org/papers/17329
https://doi.org/10.1101/388819

154: Before trilobite legs: Pygmaclypeatus daziensis reconsidered and the ancestral appendicular organization of Cambrian artiopods

Michel Schmidt, Xianguang Hou et al.

398 downloads (posted 19 Aug 2021)

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 Pygmac...

https://rxivist.org/papers/154670
https://doi.org/10.1101/2021.08.18.456779

155: Terrestrial effects of moderately nearby supernovae

Adrian L. Melott, Brian C Thomas

397 downloads (posted 08 Dec 2017)

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.

https://rxivist.org/papers/30119
https://doi.org/10.1101/230847

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

Yu Pei, Jan-Peter Duda et al.

392 downloads (posted 10 Aug 2020)

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...

https://rxivist.org/papers/94055
https://doi.org/10.1101/2020.08.10.244210

157: Foot scales in the Early Cretaceous bird Gansus yumenensis from China

Tao Zhao, Zhiheng LI et al.

392 downloads (posted 08 Jun 2021)

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...

https://rxivist.org/papers/145199
https://doi.org/10.1101/2021.06.07.447457

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

Evan Muzzall

382 downloads (posted 05 Nov 2020)

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...

https://rxivist.org/papers/103149
https://doi.org/10.1101/2020.11.04.368894

159: Holocephali From the Irati Formation (Paraná Basin), Brazil: Origin, Paleogographical and Paleoenvironmental Considerations

Artur Chahud

377 downloads (posted 10 Oct 2020)

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 ...

https://rxivist.org/papers/96509
https://doi.org/10.1101/2020.10.09.333591

160: Muon Radiation Dose and Marine Megafaunal Extinction at the end-Pliocene Supernova

Adrian L. Melott, Franciole Marinho et al.

370 downloads (posted 28 Dec 2017)

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...

https://rxivist.org/papers/30118
https://doi.org/10.1101/240093