Large trilobites in a stress-free Early Ordovician environment

International audienceUnderstanding variations in body-size is essential for deciphering the response of an organism to its surrounding environmental conditions and its ecological adaptations. In modern environments, large marine animals are mostly found in cold waters. However, numerous parameters can influence body size variations other than temperatures, such as oxygenation, nutrient availability, predation, or physical disturbances by storms. Here, we investigate trilobite size variations in the Lower Ordovician Fezouata Shale deposited in a cold water environment. Trilobite assemblages dominated by small-to normal-sized specimens that are few cm in length are found in proximal and intermediate settings, while those comprising larger taxa more than 20cm in length are found in the most distal environment of the Fezouata Shale. Drill core material from distal settings shows that sedimentary rocks hosting large trilobites preserved in-situ are extensively bioturbated with a high diversity of trace fossils, indicating that oxygen and nutrients were available in this environment. In intermediate and shallow settings, bioturbation is less extensive and shallower in depth. The rarity of storm events (minimal physical disturbance) and the lack of predators in deep environments in comparison to shallower settings would have also helped trilobites attain larger body sizes. This highly resolved spatial study investigating the effects of numerous biotic and abiotic parameters on body size has wider implications for the understanding of size fluctuations over geological time

New thylacocephalans from the Early Triassic Paris Biota (Bear Lake County, Idaho, USA).

International audienceTwo new genera and species of thylacocephalans (Arthropoda, Thylacocephala), Parisicaris triassica Charbonnier and Ligulacaris parisiana Charbonnier, are described from the early Spathian Paris Biota. These new occurrences are the first reports of thylacocephalans from Triassic rocks in North America. They considerably enlarge the spatiotemporal distribution of these enigmatic arthropods and highlight their relatively high generic richness during the Early Triassic. It also confirms that the Triassic was the taxonomically richest period for Thylacocephala

Anatomy and evolution of the first Coleoidea in the Carboniferous

Coleoidea (squids and octopuses) comprise all crown group cephalopods except the Nautilida. Coleoids are characterized by internal shell (endocochleate), ink sac and arm hooks, while nautilids lack an ink sac, arm hooks, suckers, and have an external conch (ectocochleate). Differentiating between straight conical conchs (orthocones) of Palaeozoic Coleoidea and other ectocochleates is only possible when rostrum (shell covering the chambered phragmocone) and body chamber are preserved. Here, we provide information on how this internalization might have evolved. We re-examined one of the oldest coleoids, Gordoniconus beargulchensis from the Early Carboniferous of the Bear Gulch Fossil-Lagerstätte (Montana) by synchrotron, various lights and Reflectance Transformation Imaging (RTI). This revealed previously unappreciated anatomical details, on which we base evolutionary scenarios of how the internalization and other evolutionary steps in early coleoid evolution proceeded. We suggest that conch internalization happened rather suddenly including early growth stages while the ink sac evolved slightly later

Soft tissue associations reveal the influence of preservation on biodiversity in Burgess Shale-type fossil deposits

International audienc

Taphonomic pathway of exceptionally preserved fossils in the Lower Ordovician of Morocco

International audienc

Ammonoids and nautiloids from the earliest Spathian Paris Biota and other early Spathian localities in southeastern Idaho, USA.

24 pagesInternational audienceIntensive sampling of three earliest Spathian sites represented by the Lower Shale unit and coeval bedswithin the Bear Lake vicinity and neighboring areas, southeastern Idaho, yielded several new ammonoidand nautiloid assemblages. These new occurrences overall indicate that the lower boundary of theTirolites beds, classically used as a regional marker for the base of the early Spathian, and therefore theregional Smithian/Spathian boundary, must be shifted downward into the Lower Shale unit and coevalbeds. Regarding ammonoids, one new genus (Caribouceras) and two new species (Caribouceras slugenseand Albanites americanus) are described. In addition, the regional temporal distribution of Bajarunia,Tirolites, Columbites, and Coscaites is refined, based on a fourth sampled site containing a newly reportedoccurrence of the early Spathian Columbites fauna in coeval beds of the Middle Shale unit. As acomplement to ammonoids, changes observed in nautiloid dominance are also shown to facilitatecorrelation with high-latitude basins such as Siberia during this short time interval, and they alsohighlight the major successive environmental fluctuations that took place during the late Smithian–earlySpathian transition

Glow in the dark: use of synchrotron μXRF trace elemental mapping and multispectral macro-imaging on fossils from the Paris Biota (Bear Lake County, Idaho, USA).

International audienceThe end-Permian mass extinction is the largest global-scale event ever recorded; it also corresponds to the expansion of the Modern Evolutionary Fauna, which will lead to present-day ecosystems. The Early Triassic is thus a pivotal interval in the evolution of many marine groups. An exceptionally well-preserved early Spathian fossil assemblage, the Paris Biota, was recently discovered in southeastern Idaho, USA; it represents the earliest complex marine ecosystem known to date for the post-crisis aftermath. Here we use synchrotron μXRF imaging to retrieve further anatomical, paleobiological and taphonomical data on some of the most intriguing fossils from the Paris Biota, such as contours of the central disc and the full length of arms in an ophiuroid specimen. We also show that multispectral macro-imaging is powerful to reveal or enhance the visualization of some specimens, particularly shrimps, that are barely perceptible under visible and UV lights. The complementary use of both techniques suggests that the actual richness and abundance of organisms in this exceptionally well-preserved Early Triassic ecosystem is likely to remain underestimated, and this situation may be even worse in other less well-preserved spatiotemporal contexts

Safeplatoon: surete de convois de vehicules autonomes

International audienc