Search results for "EH"
showing 10 items of 33700 documents
Detailed record of the mid-Oxfordian (Late Jurassic) positive carbon-isotope excursion in two hemipelagic sections (France and Switzerland): A plate …
2007
14 pages; International audience; The Oxfordian (Late Jurassic) was a time of widespread change in Jurassic marine (carbonate) sedimentation patterns. A marked positive excursion in δ13C is dated as Middle Oxfordian in age. In this study we investigate if changes in carbonate sedimentation coincided with altered carbon cycling and climate. We use C-isotope records as a proxy for the evolution of the carbon cycle and compare δ13C-trends with the evolution of sedimentation in a segment of the opening Tethys seaway. One of the studied sections is located in the Subalpine basin of France (Trescléoux and Oze), the other in the Swiss Jura mountains (Liesberg). Carbon-isotope stratigraphy of carbo…
Dental microwear texture analysis on extant and extinct sharks : Ante- or post-mortem tooth wear?
2020
Sharks are apex-predators that play an important role in past and present aquatic food webs. However, their diet - especially in extinct species - is often not well constrained. Dental microwear texture analysis (DMTA) has been successfully applied to reconstruct diet and feeding behaviours of different aquatic and terrestrial vertebrates. However, unlike in mammals, food-to-tooth contact in sharks is rather limited because only larger prey is manipulated before swallowing. Together with a fast tooth replacement rate, this reduces wear on individual teeth. Here, we present an explorative study of dental microwear texture on extant and extinct sharks to test whether ante-mortem wear is relat…
A low seasonality scenario in the Mediterranean Sea during the Calabrian (Early Pleistocene) inferred from fossil Arctica islandica shells
2017
Understanding past seasonal temperature variability in the ocean is essential to evaluate the effects of future climate change on marine ecosystems. Here, we estimate seasonal water temperature amplitudes from stable oxygen isotope (δ18Oshell) values of fossil shells of Arctica islandica (assuming δ18Owater= + 0.9 ± 0.1â° V-SMOW). Specimens were collected from three Pleistocene successions (Emilian and Sicilian substages of the Calabrian) in Central and Southern Italy (i.e., Rome, Lecce and Sicily). Biostratigraphic analyses from Rome Quarry deposits indicate an age between 1.6 and 1.2 Ma, whereas Sicily and Lecce successions are slightly more recent (between 1.1 and 0.62 Ma). Prior to …
Marine Early Triassic Actinopterygii from Elko County (Nevada, USA): implications for the Smithian equatorial vertebrate eclipse
2017
AbstractThe Early Triassic vertebrate record from low paleolatitudes is spotty, which led to the notion of an ‘equatorial vertebrate eclipse’ during the Smithian. Here we present articulated ray-finned fishes (Actinopterygii), collected from the marine Lower Triassic Thaynes Group at three new localities in Elko County (Nevada, USA), which were deposited within the equatorial zone. From the Smithian of the Winecup Ranch, we describe two partial skulls of the predatory actinopterygianBirgeria(Birgeriidae), attributed toB.americananew species andBirgeriasp.Birgeria americanan. sp. is distinguished from other species by a less reduced operculogular series. With an estimated total length of 1.7…
Transient metazoan reefs in the aftermath of the end-Permian mass extinction
2011
5 pages; International audience; Recovery from the devastating Permian-Triassic mass extinction about 252 million years ago is usually assumed to have spanned the entire 5 million years of the Early Triassic epoch1,2. The post-crisis interval was characterized by large-scale fluctuations of the global carbon cycle and harsh marine conditions, including a combination of ocean acidification, euxinia, and fluctuating productivity3. During this interval, metazoan-dominated reefs are thought to have been replaced by microbial deposits that are considered the hallmark of the Early Triassic4-7. Here we use field and microscopic investigations to document Early Triassic bioaccumulations and reefs f…
New research on the development of high-resolution palaeoenvironmental proxies from geochemical properties of biogenic carbonates
2017
Abstract Geochemical signatures from biogenic carbonates are being increasingly employed as palaeoenvironmental proxies. In turn, many of these proxy archives including mollusc shells, corals, and otoliths have periodic growth structures, which allow the reconstruction of chronologically constrained records of palaeoenvironmental variability at unparalleled high temporal resolution. Studying the growth and chemistry of these periodic growth structures is known as sclerochronology. Biogenic hard parts accumulate in geological or archaeological deposits, and can be directly dated using radiometric and racemisation methods. They therefore offer the opportunity for high-resolution palaeoenviron…
Permian-Triassic extinctions and rediversifications.
2015
Ammonoids were a major component of Permian marine faunas, but were on the verge of extinction during the Permian-Triassic crisis ~ 252 myr ago. Despite the severity of this extinction, their recovery was explosive in less than 1.5 myr. By Smithian time, they had already reached levels of taxonomic richness much higher than those of the Permian. The causes for the rapid Early Triassic diversification and proliferation of these organisms still remain elusive, but the evolution of their spatio-temporal diversity and disparity patterns closely correlates with the numerous environmental changes recorded during this time interval.
Revision of the genus Anasibirites Mojsisovics (Ammonoidea): An iconic and cosmopolitan taxon of the late Smithian (Early Triassic) extinction
2016
34 pages; International audience; The family Prionitidae Hyatt represents a major component of ammonoid faunas during the Smithian (Early Triassic), and the genus Anasibirites Mojsisovics is the most emblematic taxon of this family. Its stratigraphical range is restricted to the beginning of the late Smithian (Wasatchites distractus Zone). The genus is also characterized by an unusual cosmopolitan distribution, thus contrasting with most earlier Smithian ammonoid distributions that were typically restricted by latitude. Because the late Smithian witnessed an extinction of the nekton (e.g. ammonoids, conodonts) whose amplitude is equal to or larger than that of the end-Permian crisis, the nu…
Trilobites from the Red Fauna (latest Emsian, Devonian) of Hamar Laghdad, Morocco and their biodiversity
2018
36 pages; International audience; Trilobites are widespread in Early Devonian deposits of north Gondwana; some of the most emblematic ones were collected from the famous latest Emsian (Early Devonian) mudmound locality Hamar Laghdad in south-eastern Morocco. This locality is famous for its trilobites, especially for the conspicuous red-coloured remains of phacopid trilobites with often greenish eyes. Here, we present a taxonomic revision of the previously described trilobites from the so-called Red Fauna of Hamar Laghdad. We introduce the new taxa Harpes hamarlaghdadensis n. sp. and Morocops davidbrutoni n. sp. Phacopids dominate the trilobite assemblage from the Red Cliff at Hamar Laghdad …
Seasonal and habitat effects on the nutritional properties of savanna vegetation: Potential implications for early hominin dietary ecology.
2019
The African savannas that many early hominins occupied likely experienced stark seasonality and contained mosaic habitats (i.e., combinations of woodlands, wetlands, grasslands, etc.). Most would agree that the bulk of dietary calories obtained by taxa such as Australopithecus and Paranthropus came from the consumption of vegetation growing across these landscapes. It is also likely that many early hominins were selective feeders that consumed particular plants/plant parts (e.g., leaves, fruit, storage organs) depending on the habitat and season within which they were foraging. Thus, improving our understanding of how the nutritional properties of potential hominin plant foods growing in mo…