Hasil untuk "Paleontology"

Guillermina Sánchez Vuichard, Nerina Pisani, Carolina Vásquez et al.

The Central Pampa plain (36º–37º S; 60º–61º W) presents numerous shallow lakes subjected to climatic dynamics and anthropogenic impacts during the Late Holocene, but few were analyzed. New studies are essential to provide an integral and regional analysis of these lakes evolution. In this context, a multi-indicator analysis including sedimentary and palynomorph (pollen and non-pollen) indicators was performed to reconstruct the paleoenvironmental evolution of Blanca Chica shallow lake during the past 1700 years. Four main lake condition stages were identified. Natural forcing dominated the period prior to 1880 CE, followed by a scenario characterized by the combined action of anthropic and natural forcings. Between 260800 CE, laminated sediments and phytoplankton dominance point to a high-level, turbid, nutrient rich lake during a wet period. Between 800–1600 CE, massive sediments, increasing halophytic vegetation and decreasing phytoplankton indicate a lower water-lake level in a dry context. This drought scenario was intensified between 1660–1830 CE as suggested by massive mottled sediments, submerged macrophytes remains and filamentous chlorophytes. A shift to wetter conditions is indicated for 1830–2015 CE, by a perennial, turbid, eutrophic, high-level lake with massive organic sediments. The onset of agriculture and cattle was shown by a raise in pollen taxa (i.e., 1830) and increased sedimentation rates related to soils erosion which suggested intense anthropic activity. The change in the aquatic communities and sedimentology for the last 30 years allowed considering a shift to high anthropogenic impact combined with an increase in precipitation which generated an accelerated eutrophication of the lake.

Bryce E. Koester, Bryce E. Koester, John C. Handley et al.

Pteropods are marine planktonic snails that are used as bioindicators of ocean acidification due to their thin, aragonitic shells, and ubiquity throughout the world’s oceans; their responses include decreased size, reduced shell thickness, and increased shell dissolution. Shell dissolution has been measured with a variety of metrics involving light microscopy, scanning electron microscopy (SEM), and computed tomography (CT). While CT and SEM metrics offer high resolution imaging, these analyses are cost- and time-intensive relative to light microscopy analysis. This research compares light microscopy, CT, and SEM shell dissolution metrics across three pteropod species: Limacina helicina, Limacina retroversa, and Heliconoides inflatus. Sourced from multiple localities, these specimens lived in tropical to subpolar environments and were exposed to varying aragonite saturations states due to oceanographic differences in these environments. Specimens were evaluated with light microscopy for the Limacina Dissolution Index (LDX), with SEM for percent of pristine shell coverage and maximum dissolution type, and with CT for whole-shell thickness. LDX and the percentage of pristine shell determined via SEM were highly correlated in all three species’ datasets. For L. retroversa, LDX was also significantly correlated to SEM maximum dissolution type. Although the genera Heliconoides and Limacina have different shell microstructures, the relationship between LDX and SEM dissolution did not vary by species. The CT metric for shell thickness was not significantly correlated to any other dissolution metrics for any species. However, severely dissolved areas apparent in SEM were visually discernible in CT thickness heatmaps. While CT may not detect minor shell dissolution, previous studies have used CT to detect reduced calcification in response to ocean acidification. SEM is ideal for detecting the onset of dissolution, but SEMing large numbers of specimens may not be practical due to monetary and time constraints. LDX, on the other hand, is a fast and cost-effective metric that is strongly correlated with SEM metrics, regardless of the oceanographic conditions that those species experienced. These results suggest that an efficient ocean acidification monitoring strategy is to evaluate all pteropod specimens via LDX and to then SEM a subset of those specimens.

Grace Tatiana Páez-Barrera, Karla Vizuete, Juan José Ortiz-Aguilu et al.

Several samples of fossilized wood (charcoal) were collected in the Papayita archaeological site, in coastal Ecuador. This carbonized material was encountered inside a layer of volcanic ash that sealed the site. The ash-sized tephra was produced by a sub-Plinian eruption from the Guagua Pichincha volcano contemporaneous with the late Valdivia phases during the Formative Period. Each of the samples was sectioned into 10 to 15 subsamples and examined under a Scanning Electron Microscope (SEM), producing high-resolution images with a large depth of field where the anatomical structures and their geochemical composition were vividly discernible. Each sample corresponds to organic matter of vegetable origin, that is, carbonized wood in the form of small rocks, whose appearance is that of carbonized woody tree trunks and or branches. We were able to observe vascular structures, specifically bundles of xylem. It was possible to conclude that these tracheids underwent a physicochemical transformation typical of petrification processes, leaving the molds intact. This allowed us to determine structural elements that support the identification of the group of plants to which these samples belong, through the methodology of comparison of the anatomical components of current species. The fossilized wood structures are three-dimensional and present characteristics that correspond to the group of higher plants, Gymnosperms, of the Podocarpaceae group. Among them, quadrangular tracheids, circular hole-shaped pits in the vascular system, and absent resin canals stand out. Central to the analysis is the presence of transverse parenchyma, which can be ascertained to correspond to vegetation from climates that are temperate or cold.

B. Charlesworth, R. Lande, M. Slatkin

Bocharov Sergei G. , Maslovskyi Andrey N.

A short essay about the second largest of group imported container amphoras on the territory of the Golden Horde which was named in scientific literature «amphoras of SSS stamp group» is presented in the article. In materials from Eastern Europe this group was singled-out by I.V. Volkov. He tracked evolution of this group throughout the 12th – 13th centuries. The authors have made an overview of the opinions of different researchers about the place of their production. At the moment, at least four options have been proposed: Palestine, Cilicia (?), Thessaloniki, Western Georgia. An opinion was expressed that it was unlawful to single out this group of amphoras. All proposed hypotheses are based on indirect data and logical constructions based on different conditions. On the opinion of the authors of the article, the amphoras of the SSS stamp group came from the territory of Western Georgia during the period of flourishing of the centralized state in Georgia. An estimate of the number of finds and the geography of their distribution are given. Also most characteristic features of the vessels of this group are characterized. Considering that during the Golden Horde period, amphoras of the SSS stamp group arrived during a few decades in the middle of the third quarter of 13th century, their identification is very important for revealing of the earliest complexes on the settled settlements of the Golden Horde.

P. Martin, R. Klein

Ariana Paulina-Carabajal, Julia Brenda Desojo

La historia de las mujeres argentinas en el desarrollo de la paleoherpetología es muy interesante y crucial, ya que la misma evidencia el rol de la mujer en el campo académico, en el ámbito familiar y en la sociedad. A lo largo de casi 100 años, las investigaciones llevadas a cabo por mujeres fueron en aumento, abarcando los principales grupos taxonómicos y generando nuevas líneas de investigación con cada generación. En la actualidad, el cambio de paradigma de la mujer en el campo de la paleontología de vertebrados en general, no solo se plasma en su rol dirigiendo campañas paleontológicas y equipos de investigación, sino que también se refleja en sus actividades de gestión y su proyección en el ámbito internacional.

Charlie A. Hamm, Oliver Hampe, Jürgen Mews et al.

Abstract Dual-energy computed tomography (DECT) is an imaging technique that combines nondestructive morphological cross-sectional imaging of objects and the quantification of their chemical composition. However, its potential to assist investigations in paleontology has not yet been explored. This study investigates quantitative DECT for the nondestructive density- and element-based material decomposition of fossilized bones. Specifically, DECT was developed and validated for imaging-based calcium and fluorine quantification in bones of five fossil vertebrates from different geological time periods and of one extant vertebrate. The analysis shows that DECT material maps can differentiate bone from surrounding sediment and reveals fluorine as an imaging marker for fossilized bone and a reliable indicator of the age of terrestrial fossils. Moreover, the jaw bone mass of Tyrannosaurus rex showed areas of particularly high fluorine concentrations on DECT, while conventional CT imaging features supported the diagnosis of chronic osteomyelitis. These findings highlight the relevance of radiological imaging techniques in the natural sciences by introducing quantitative DECT imaging as a nondestructive approach for material decomposition in fossilized objects, thereby potentially adding to the toolbox of paleontological studies.

A. Love, M. Grabowski, D. Houle et al.

Abstract. The concept of evolvability—the capacity of a population to produce and maintain evolutionarily relevant variation—has become increasingly prominent in evolutionary biology. Paleontology has a long history of investigating questions of evolvability, but paleontological thinking has tended to neglect recent discussions, because many tools used in the current evolvability literature are challenging to apply to the fossil record. The fundamental difficulty is how to disentangle whether the causes of evolutionary patterns arise from variational properties of traits or lineages rather than being due to selection and ecological success. Despite these obstacles, the fossil record offers unique and growing sources of data that capture evolutionary patterns of sustained duration and significance otherwise inaccessible to evolutionary biologists. Additionally, there exist a variety of strategic possibilities for combining prominent neontological approaches to evolvability with those from paleontology. We illustrate three of these possibilities with quantitative genetics, evolutionary developmental biology, and phylogenetic models of macroevolution. In conclusion, we provide a methodological schema that focuses on the conceptualization, measurement, and testing of hypotheses to motivate and provide guidance for future empirical and theoretical studies of evolvability in the fossil record.

A. Ijspeert

A milestone in vertebrate evolution, the transition from water to land, owes its success to the development of a sprawling body plan that enabled an amphibious lifestyle. The body, originally adapted for swimming, evolved to benefit from limbs that enhanced its locomotion capabilities on submerged and dry ground. The first terrestrial animals used sprawling locomotion, a type of legged locomotion in which limbs extend laterally from the body (as opposed to erect locomotion, in which limbs extend vertically below the body). This type of locomotion—exhibited, for instance, by salamanders, lizards, and crocodiles—has been studied in a variety of fields, including neuroscience, biomechanics, evolution, and paleontology. Robotics can benefit from these studies to design amphibious robots capable of swimming and walking, with interesting applications in field robotics, in particular for search and rescue, inspection, and environmental monitoring. In return, robotics can provide useful scientific tools to test hypotheses in neuroscience, biomechanics, and paleontology. For instance, robots have been used to test hypotheses about the organization of neural circuits that can switch between swimming and walking under the control of simple modulation signals, as well as to identify the most likely gaits of extinct sprawling animals. Here, I review different aspects of amphibious and sprawling locomotion, namely gait characteristics, neurobiology, numerical models, and sprawling robots, and discuss fruitful interactions between robotics and other scientific fields.

J. Szwedo, Bo Wang, Agnieszka Soszyńska-Maj et al.

Following a mailbox of comments concerning a letter sent by the Society of Vertebrate Paleontology to journal editors on “Fossils from conflict zones...” dated 21 April 2020 calling for a ban on publications on Burmese amber, it was felt necessary to air some concerns raised for further discussion.

Lionel Hautier

Sharon May-Davis, Robert Hunter, Wendy Brown

The lateral profile of the 6th and 7th cervical spinous processes (CSPs) were examined in four extant species of Equus (n=33); E. caballus (n=26), E. przewalskii (n=3), E. quagga boehmi (n=1), E. asinus (n=3) and compared to pre-domesticated Equus specimens (n=66) representing three known species: E. occidentalis (n=56), E. mosbachensis (n=2), E. curvedins/insulatis (n=1) and unknown Equus species (n=7) from five museums. Six common morphological profiles were revealed: cuneate, curvate, falcate, rudimentary, scalenate, and truncate. For the 6th CSP, the distribution of these morphologies amongst extant Equus is: cuneate, only E. asinus; curvate, E. caballus and E. przewalskii always in combination with ligamentum lamina nuchae (lig. lamina nuchae) attachments from the 2nd through to 7th CSP inclusive; falcate, E. caballus and E. przewalskii always in combination with lig. lamina nuchae attachments from the 2nd through to 7th CSP inclusive; rudimentary, E. caballus always associated with lig. lamina nuchae attachments from the 2nd through to 5th CSP inclusive; scalenate, E. caballus in association with lig. lamina nuchae attachments from the 2nd through to 5th (n=11) or 7th (n=4) CSP inclusive; truncate, not present. The 6th CSP in museum specimens of Equus exhibits one of four profiles: cuneate (n=10), curvate (n=14), scalenate (n=11) and truncate (n=4). For the 7th CSP, the distribution of these morphologies amongst extant Equus is: curvate, E. caballus mostly associated with lig. lamina nuchae attachments from the 2nd through to 5th CSP inclusive, falcate, E. caballus mostly associated with lig. lamina nuchae attachments from the 2nd through to 7th CSP inclusive, scalenate, E. caballus associated with lig. lamina nuchae attachments from the 2nd through to 5th CSP inclusive. Only Rancho La Brea and Tar Pits Museum provided samples suitable for examination of the 7th CSP. These exhibited four profiles: curvate (n=7), falcate (n=11), scalenate (n=2), and truncate (n=7). These findings suggest that the lateral profile of the 6th CSP is of potential use in identification of species; attachments of the lig. lamina nuchae alter the morphology of the 6th and 7th CSP; and that attachments of the lig. lamina nuchae on the 2nd to 7th CSP were likely present in species of Equus prior to domestication.

S. Nee, A. Mooers, Paul H. Harvey

Rafaella Georgiou, P. Guériau, C. Sahle et al.

X-ray Raman multispectral imaging identifies the 3D chemistry of carbon in entire organic paleontological specimens. The in situ two-dimensional (2D) and 3D imaging of the chemical speciation of organic fossils is an unsolved problem in paleontology and cultural heritage. Here, we use x-ray Raman scattering (XRS)–based imaging at the carbon K-edge to form 2D and 3D images of the carbon chemistry in two exceptionally preserved specimens, a fossil plant dating back from the Carboniferous and an ancient insect entrapped in 53-million-year-old amber. The 2D XRS imaging of the plant fossil reveals a homogeneous chemical composition with micrometric “pockets” of preservation, likely inherited from its geological history. The 3D XRS imaging of the insect cuticle displays an exceptionally well preserved remaining chemical signature typical of polysaccharides such as chitin around a largely hollowed-out inclusion. Our results open up new perspectives for in situ chemical speciation imaging of fossilized organic materials, with the potential to enhance our understanding of organic specimens and their paleobiology.

Timothy Gaudin, Susan Tuckniss, Alberto Boscaini et al.

Pronothrotherium typicum is a late Miocene–early Pliocene (Huayquerian–Chapadmalalan SALMA) nothrotheriid sloth known from the Catamarca Province of northwestern Argentina. Pronothrotherium is one of four nothrotheriid genera known from relatively complete skeletal material, but unlike the other three, the osteology of Pronothrotherium has not been formally described. The present study provides the first detailed description and illustration of the cranial anatomy of Pronothrotherium, based largely on a nearly complete, subadult skull of P. typicum from the collections of The Field Museum (Chicago, Illinois, USA), as well as a less well-preserved adult skull and isolated mandible from the same collections. A revised cranial diagnosis of P. typicum is provided in the text. The skull of this species shows a number of distinctive features, most notably a peculiar vomerine keel in the nasopharynx, terminating in a swollen knob, that is, as far we know, a unique morphology among mammals. Based on the results of the present study, there appears to be reason to recognize two contemporaneous species of Pronothrotherium, P. typicum and P. mirabilis, although the latter is less well supported. We do not accept the validity of a third described species, P. figueirasi, considering it instead to be synonymous with P. mirabilis. The present study does not resolve the uncertain phylogenetic relationships among the well-preserved nothrotheriine taxa Pronothrotherium, Mionothropus (late Miocene), and the two Pleistocene genera in Nothrotheriini, Nothrotherium and Nothrotheriops. However, we hope that the data provided will facilitate subsequent phylogenetic studies that may resolve these issues.

D. Wright

T. Deng, L. Ding

Over the last two decades, many quantitative paleoaltimetry reconstructions of the Tibetan Plateau have been published, but they are still preliminary and controversial, although several approaches have been combined paleontology and geochemistry, including vertebrate, plant, and pollen fossils as well as oxygen, carbon, and hydrogen isotopes. The Tibetan Plateau is the youngest and highest plateau on Earth, and its paleoaltimetry reconstructions are crucial to interpret its geodynamic evolution and to understand the climatic changes in Asia. Uplift histories of the Tibetan Plateau based on different proxies differ considerably, and two viewpoints are pointedly opposing on the paleoaltimetry estimations of the Tibetan Plateau. One viewpoint is that the Tibetan Plateau did not strongly uplift to reach its modern elevation until the Late Miocene, but another one, mainly based on stable isotopes, argues that the Tibetan Plateau formed early during the Indo-Asian collision and reached its modern elevation in the Paleogene or by the Middle Miocene. With either a geochemical or paleontological approach, the present is used as the key to the past. However, there are great difficulties because modern processes of isotopic fractionation and species for creature distribution are not easily precisely determined. In addition, the climatic and environmental backgrounds of past geological times have massive differences from the present, and associated adjustments are influenced by many human factors. In the future work, the applications of multidisciplinary comprehensive methods and cross-checks of their results will be productive, and we look forward to achieving more reliable estimates for paleoelevations of the Tibetan Plateau.