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Results 61 through 80 out of 190

in category paleontology

 

61: Systematic revision and redefinition of the genus Scirrotherium Edmund and Theodor, 1997 (Cingulata, Pampatheriidae): Implications for the origin of pampatheriids and the evolution of the South American lineage including Holmesina

Kevin Jiménez-Lara

919 downloads (posted 30 Jul 2019)

The intrageneric relationships of the pampatheriid genus Scirrotherium and its affinities with supposedly related genera, i.e., Kraglievichia and Holmesina , are revised through parsimony phylogenetic analyses and new comparative morphological descriptions. For this work, unpublished material of pampatheriids (numerous osteoderms, one partial skull and a few postcranial bones) from Neogene formations of Colombia was analyzed. The results show that Scirrotherium is paraphyletic if we include all its referred species, i.e., Scirrotherium hondaensis , S. carinatum and S. antelucanus . The species S. carinatum is closer to Kraglievichia paranensis than to S. hondaensis or S. antelucanus , therefore the new name K. carinatum comb. nov. is proposed. The relationship among S. hondaensis and S. antelucanus could not be resolved, so these species should be designated in aphyly. In spite of failing to recover S. hondaensis and S. antelucanus as one single clade, here is preferred to maintain the generic name Scirrotherium in both species based on diagnostic evidence. New emended diagnoses for Scirrotherium , S. hondaensis and Kraglievichia are provided. The genus Holmesina was found to be monophyletic and positioned as the sister clade of Scirrotherium + Kraglievichia . The evolutionary and biogeographic implications of the new phylogeny and taxonomic re-arrangements are discussed. A possible geographic origin of the family Pampatheriidae and Scirrotherium in low latitudes of South America as early as Early Miocene times is claimed. The South American ancestor or sister taxon of Holmesina is predicted to be morphologically more similar to Scirrotherium than to Kraglievichia .

https://rxivist.org/papers/56997
https://doi.org/10.1101/719153

62: Pushing Raman spectroscopy over the edge: purported signatures of organic molecules in fossils are instrumental artefacts

Julien Alleon, Gilles Montagnac et al.

907 downloads (posted 10 Nov 2020)

Claims for the widespread preservation of fossilized biomolecules in many fossil animals have recently been reported in six studies, based on Raman microspectroscopy. Here, we show that the putative Raman signatures of organic compounds in these fossils are actually instrumental artefacts resulting from intense background luminescence. Raman spectroscopy relies upon the detection of photons scattered inelastically by matter as a result of its interaction with a laser beam. For many natural materials, this interaction al...

https://rxivist.org/papers/103600
https://doi.org/10.1101/2020.11.09.375212

63: Anamorphic development and extended parental care in a 520 million-year-old stem-group euarthropod from China

Dongjing Fu, Javier Ortega-Hernandez et al.

905 downloads (posted 15 Feb 2018)

Extended parental care (XPC) is a complex reproductive strategy in which progenitors actively look after their offspring up to - or beyond - the first juvenile stage in order to maximize their fitness. Although the euarthropod fossil record has produced several examples of brood-care, the appearance of XPC within this phylum remains poorly constrained given the scarcity of developmental data for Palaeozoic stem-group representatives that would link juvenile and adult forms in an ontogenetic sequence. Here, we describe t...

https://rxivist.org/papers/30115
https://doi.org/10.1101/266122

64: Cranial anatomy of the predatory actinopterygian Brazilichthys macrognathus from the Permian (Cisuralian) Pedra de Fogo Formation, Parnaíba Basin, Brazil

Rodrigo T. Figueroa, Matt Friedman et al.

900 downloads (posted 05 Feb 2019)

Brazilichthys macrognathus is the only named actinopterygian from the Permain (Cisuralian) Pedra de Fogo Formation of northeastern Brazil, where it is represented by a single three-dimensionally preserved but incompletely described skull of unclear systematic placement. We used X-ray computed microtomography (μ-CT) to better document its anatomy and phylogenetic affinities. μ-CT reveals parts of the internal skeleton. We correct errors in original description, including the number of infraorbital bones and the misidenti...

https://rxivist.org/papers/43316
https://doi.org/10.1101/540310

65: The R package divDyn for quantifying diversity dynamics using fossil sampling data

Kocsis Á. T., Reddin C. J. et al.

894 downloads (posted 23 Sep 2018)

Unbiased time series of diversity dynamics are vital for quantifying the grand history of life. Applications include identifying ancient mass extinctions and inferring both biotic and abiotic controls on diversification rates. We introduce divDyn, a new R package that facilitates the calculation of taxonomic richness, extinction and origination rates from time-binned fossil sampling data. State-of-the-art sampling completeness metrics, counting protocols, and sampling standardisation functions permit the reconstruction ...

https://rxivist.org/papers/33283
https://doi.org/10.1101/423780

66: Constructing a Timescale of Biotic Recovery across the Cretaceous Paleogene Boundary, Corral Bluffs, Denver Basin, Colorado

Anthony J Fuentes, William C. Clyde et al.

890 downloads (posted 15 May 2019)

The Cretaceous-Paleogene (K-Pg) boundary interval represents one of the most significant mass extinctions and ensuing biotic recoveries in Earth history. Earliest Paleocene fossil mammal faunas corresponding to the Puercan North American Land Mammal Age (NALMA) are thought to be highly endemic and potentially diachronous, necessitating precise chronostratigraphic controls at key fossil localities to constrain recovery dynamics in continental biotas following the K-Pg mass extinction. The Laramide synorgenic sedimentary ...

https://rxivist.org/papers/50733
https://doi.org/10.1101/636951

67: NON-AVIAN DINOSAUR EGGSHELL CALCITE CONTAINS ANCIENT, ENDOGENOUS AMINO ACIDS

Evan T. Saitta, Jakob Vinther et al.

874 downloads (posted 03 Jun 2020)

Rates of peptide bond hydrolysis and other diagenetic reactions are not favourable for Mesozoic protein survival. Proteins hydrolyse into peptide fragments and free amino acids that, in open systems such as bone, can leach from the specimen and be further degraded. However, closed systems are more likely to retain degradation products derived from endogenous proteins. Amino acid racemisation data in experimental and subfossil material suggests that mollusc shell and avian eggshell calcite crystals can demonstrate closed...

https://rxivist.org/papers/85902
https://doi.org/10.1101/2020.06.02.129999

68: Fables and foibles: a critical analysis of the Palaeoflora database and the Coexistence approach for palaeoclimate reconstruction

Guido W. Grimm, Johannes M. Bouchal et al.

873 downloads (posted 10 Mar 2015)

The “Coexistence Approach” is a mutual climate range (MCR) technique combined with the nearest-living relative (NLR) concept. It has been widely used for palaeoclimate reconstructions based on Eurasian plant fossil assemblages, most of them palynofloras (studied using light microscopy). The results have been surprisingly uniform, typically converging to subtropical, per-humid or monsoonal conditions. Studies based on the coexistence approach have had a marked impact in literature, generating over 10,000 citations thus f...

https://rxivist.org/papers/30136
https://doi.org/10.1101/016378

69: Life histories and niche dynamics in late Quaternary proboscideans from Midwestern North America: evidence from stable isotope analyses

Chris Widga, Greg Hodgins et al.

864 downloads (posted 09 Jan 2020)

Stable isotopes of mammoths and mastodons have the potential to illuminate ecological changes in late Pleistocene landscapes and megafaunal populations as these species approached extinction. The ecological factors at play in this extinction remain unresolved, but isotopes of bone collagen (δ13C, δ15N) and tooth enamel (δ13C, δ18O, 87Sr/86Sr) from the Midwest, USA are leveraged to examine ecological and behavioral changes that occurred during the last interglacial-glacial cycle. Both species had significant C3 contribut...

https://rxivist.org/papers/70517
https://doi.org/10.1101/2020.01.08.896647

70: Automated Microfossil Identification and Segmentation Using a Deep Learning Approach

L.E Carvalho, G. Fauth et al.

832 downloads (posted 06 Jun 2019)

The applicability of computational analysis to paleontological images ranges from the study of the animals, plants and evolution of microorganisms to the simulation of the habitat of living beings of a given epoch. It also can be applied in several niches, such as oil exploration, where there are several factors to be analyzed in order to minimize the expenses related to the oil extraction process. One factor is the characterization of the environment to be explored. This analysis can occur in several ways: use of probe...

https://rxivist.org/papers/52665
https://doi.org/10.1101/661694

71: Petrosal morphology and cochlear function in Mesozoic stem therians

Tony Harper, Guillermo Rougier

830 downloads (posted 07 Dec 2018)

Here we describe the bony anatomy of the inner ear and surrounding structures seen in three of the most plesiomorphic crown mammalian petrosal specimens in the fossil record. Our study sample includes the stem therian taxa Priacodon fruitaensis from the Upper Jurassic of North America, and two isolated petrosal specimens colloquially known as the Höövör petrosals, recovered from Aptian-Albian sediments in Mongolia. The second Höövör petrosal is here described at length for the first time. All three of these stem therian...

https://rxivist.org/papers/38456
https://doi.org/10.1101/490367

72: A late Permian ichthyofauna from the Zechstein Basin, Lithuania-Latvia Region

Darja Dankina-Beyer, Andrej Spiridonov et al.

818 downloads (posted 20 Feb 2019)

The late Permian is a transformative time, which ended in one of the most significant extinction events in Earth's history. Fish assemblages are a major component of marine foods webs. The macroevolution and biogeographic patterns of late Permian fish are currently insufficiently known. In this contribution, the late Permian fish fauna from Kūmas quarry (southern Latvia) is described for the first time. As a result, the studied late Permian Latvian assemblage consisted of isolated chondrichthyan teeth of Helodus sp., ?A...

https://rxivist.org/papers/44368
https://doi.org/10.1101/554998

73: The dynamics of stem and crown groups

Graham E Budd, Richard P. Mann

812 downloads (posted 09 May 2019)

The fossil record of the origins of major groups is of great interests to many biologists, especially when the fossil record apparently conflicts with timings based on molecular clock estimates. Here we model the diversity of 'stem' (basal) and 'crown' (modern) members of groups as seen in the fossil record, using a 'birth-death model'. Under background conditions, the stem group members must diversify rapidly until the modern crown group emerges, at which point their diversity rapidly collapses, followed shortly by the...

https://rxivist.org/papers/50355
https://doi.org/10.1101/633008

74: Classification of down-core foraminifera image sets using convolutional neural networks.

Ross Marchant, Martin Tetard et al.

806 downloads (posted 13 Nov 2019)

Manual identification of foraminifera species or morphotypes under stereoscopic microscopes is time-consuming for the taxonomist, and a long-time goal has been automating this process to improve efficiency and repeatability. Recent advances in computation hardware have seen deep convolutional neural networks emerge as the state-of-the-art technique for image-based automated classification. Here, we describe a method for classifying large down-core foraminifera image set using convolutional neural networks. Construction ...

https://rxivist.org/papers/66130
https://doi.org/10.1101/840926

75: Crocodylomorph cranial shape evolution and its relationship with body size and ecology

Pedro L. Godoy

805 downloads (posted 05 Aug 2019)

Crocodylomorpha, which includes living crocodylians and their extinct relatives, has a rich fossil record, extending back for more than 200 million years. Unlike modern semi-aquatic crocodylians, extinct crocodylomorphs exhibited more varied lifestyles, ranging from marine to fully terrestrial forms. This ecological diversity was mirrored by a remarkable morphological disparity, particularly in terms of cranial morphology, which seems to be closely associated with ecological roles in the group. Here, I use geometric mor...

https://rxivist.org/papers/57490
https://doi.org/10.1101/724609

76: Diverse stem-chondrichthyan oral structures and evidence for an independently acquired acanthodid dentition

Richard P Dearden, Sam Giles

791 downloads (posted 10 Jul 2020)

The teeth of sharks famously form a series of parallel, continuously replacing files borne directly on the jaw cartilages, in contrast to the site-specific, dermal plate-borne dentition of bony fishes. A major obstacle in understanding how this system evolved is the poorly understood relationships of the earliest chondrichthyans and the profusion of morphologically and terminologically diverse bones, cartilages, splints and whorls that they possess. Here we use tomographic methods to investigate mandibular structures in...

https://rxivist.org/papers/90578
https://doi.org/10.1101/2020.07.08.193839

77: A Whole-Plant Monocot from the Early Cretaceous

Zhong-Jian Liu, Li-Jun Chen et al.

787 downloads (posted 17 Apr 2018)

The Yixian Formation (the Lower Cretaceous) of China is world famous for its fossils of early angiosperms. Although these diverse angiosperms demonstrate an unexpectedly great diversity, few are preserved as whole plants (not mention of monocots), making our understanding of them incomplete. Here, we report a fossil angiosperm, Sinoherba ningchenensis gen. et sp. nov (Sinoherbaceae fam. nov.), from the Yixian Formation of China; this fossil has a physically connected underground stem with fibrous rootlets, a stem with b...

https://rxivist.org/papers/30113
https://doi.org/10.1101/302075

78: A new method for enamel amino acid racemization dating: a closed system approach

Marc R. Dickinson, Adrian M Lister et al.

786 downloads (posted 25 Oct 2018)

Analysis of the predictable breakdown of proteins and amino acids in ancient biominerals enables age estimation over the Quaternary. We postulate that enamel is a suitable biomineral for the long-term survival of endogenous amino acids. Analysis of multiple amino acids for geochronological studies is typically achieved using a RP-HPLC method. However, the low concentrations of amino acids coupled with high concentrations of inorganic species make accurate determination of amino concentrations challenging. We have develo...

https://rxivist.org/papers/35342
https://doi.org/10.1101/453340

79: An early Cambrian ecdysozoan with a terminal mouth but no anus

Yunhuan Liu, Huaqiao Zhang et al.

765 downloads (posted 06 Sep 2020)

The ecdysozoans are the most diverse animal group on Earth[1][1], [2][2]. Molecular clock studies indicate that the ecdysozoans may have diverged and diversified in the Ediacaran Period[3][3], [4][4], but unambiguous ecdysozoan fossils first appear in the earliest Cambrian and are limited to cycloneuralians[5][5]–[7][6]. Here we report new material of the early Cambrian microscopic animal Saccorhytus coronarius , which was previously interpreted as a deuterostome[8][7]. Saccorhytus coronarius is reconstructed as a milli...

https://rxivist.org/papers/100151
https://doi.org/10.1101/2020.09.04.283960

80: Late Holocene land vertebrate fauna from Cueva de los Nesofontes, Western Cuba: stratigraphy, last appearance dates, diversity and paleoecology

Johanset Orihuela, Leonel Pérez Orozco et al.

755 downloads (posted 17 Jan 2020)

Here we report a Late Holocene fossil-rich cave deposit from Cueva de los Nesofontes, Mayabeque Province, Cuba. The deposit formation and its fauna were studied through a multidisciplinary approach that included stable isotope analyses, radiocarbon chronology, stratigraphy, sedimentology, and taphonomy. Thousands of microvertebrate skeletal remains were recovered, representing a diverse land vertebrate fauna that included threatened and extinct species. The deposit is characterized by profuse Nesophontes remains due to ...

https://rxivist.org/papers/71284
https://doi.org/10.1101/2020.01.17.909663