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

An Early Triassic gladius associated with soft tissue remains from Idaho, USA - a squid-like coleoid cephalopod at the onset of Mesozoic Era.

15 pagesInternational audienceWe describe an Olenekian (Early Triassic) “fossil squid” belonging to the oldest complex Mesozoic marine biota collected in the Lower Shale unit of the Lower Triassic Thaynes Group in Idaho, USA. The studied specimen shows a tapered structure embedded in a cylindrical soft body. Morphological, ultrastructural and geochemical features of the specimen suggest that it corresponds to an internally-shelled cephalopod exhibiting a tapered micro-laminated gladius with rachis, narrow median and lateral fields and a large conus; a pair of posterior large fin-supported cartilages and fins; ventral and dorsal mantle band-shape structures, the dorsal one being cartilaginous; mantle patches; a stomach containing undigested arm-hooks and sheet-like pieces of potential flooded ink. Coupled SEM/EDS analyses show that (i) arm-hooks and ink were pseudomorphed by nanoparticles (less than 0.6 mm in diameter) of carbon, (ii) gladius and soft tissues were substituted by granules of calcium phosphate, (iii) cartilage canalicula’s were partially filled with calcium phosphate grains and crystals of Zn- and S-containing minerals. The specimen was hence probably fossilized due to metabolism of P- and C-accumulating bacteria. Based on this specimen, Idahoteuthis parisiana Doguzhaeva and Brayard gen. et sp. nov. and Idahoteuthidae Doguzhaeva and Brayard fam. nov. are erected. This family is characterized by an elongated, cylindrical, dorsally cartilaginous muscular mantle; well-developed, about 0.2 mantle length, rounded anteriorly and acute posteriorly, fin-supported cartilages and similarly shaped two fins at conical mantle termination, and thin slender gladius with narrow median and lateral fields, rachis and breviconic conus. This family assumedly falls in Myopsida (Decabrachia). A streamlined body, large fin-supported cartilages and eroded arm-hooks in the stomach of Idahoteuthis Doguzhaeva and Brayard gen. nov. suggest that this was a maneuverable cannibal predator that dwelled in the subequatorial shallow sea of the west coast of Pangaea

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

A new holocrinid (Articulata) from the Paris Biota (Bear Lake County, Idaho, USA) highlights the high diversity of Early Triassic crinoids.

9 pagesInternational audienceAfter the end-Permian crisis and the extinction of their four Paleozoic subclasses, crinoids rapidly recovered. This group is classically believed to have radiated from a small surviving clade and to have diversified during the Middle and Upper Triassic from two lineages. Nevertheless, recent findings suggested that several lineages of crinoids had already diversified during the Early Triassic, and that their diversity has been overlooked. Here we describe a new form of holocrinid, Holocrinus nov. sp., from the earliest Spathian (Early Triassic) of southeastern Idaho (USA). So far, the exceptional completeness of sampled specimens, with skeletal elements of arms and stem in connection, is unique for the Early Triassic. They show that derived morphological features had already evolved ∼1.3 million years after the Permian–Triassic boundary, supporting the scenario of a rapid Early Triassic diversification of crinoids

Deciphering the exceptional preservation of the Early Triassic Paris Biota (Bear Lake County, Idaho, USA).

13 pagesInternational audienceAfter the end-Permian mass extinction, the Early Triassic (∼251.9 to 247 Ma) is characterized by several biotic crises that particularly affected marine faunas; accordingly, marine ecosystems from this unstable interval have been often described as heavily depauperate. This assumption, however, may relate to a biased fossil record. The discovery of taphonomic windows, like Konservat-Lagerstätten, in the Early Triassic would help to better understand the composition and diversity of ecosystems at that time. The Paris Biota (Idaho, USA) is a highly diverse fossil assemblage from the earliest Spathian (early late Olenekian, ∼250.6 Ma), indicating a rapid rediversification for many groups after the end-Permian crisis and pointing toward a remarkably complex marine ecosystem ∼1.3 m.y. after the Permian-Triassic boundary. However, its detailed taphonomy has not yet been investigated. Here we present the mineral characterization of four of its most abundant taxa: discinoid and linguloid brachiopods, leptomitid sponges, and caridean shrimps. For this purpose, we combined data from Raman microspectroscopy, Fourier Transform InfraRed spectroscopy, and SEM-EDXS. Although all taxa were preserved in calcium phosphate, the morphology, structuring and size of crystals are highly dissimilar at a nano- to micrometric scale. In brachiopods, the ultrastructure of calcium phosphate shows unorganized bacillary-like crystals, while in crustaceans their size is considerably smaller and round-shaped. Similar small crystals are observed in sponges. However, the ultrastructure of calcium phosphate in sponges exhibits a well-defined preferential orientation. In addition, sponges show some compressed but preserved three-dimensional features, with an inner surface better preserved. Such analyses are essential to understand the taphonomic pathways enabling exceptional preservation. The further comprehension of preservation features would help to understand potential bias on observed diversity signals and their interpretation

A new brittle star (Ophiuroidea: Ophiodermatina) from the Early Triassic Paris Biota (Bear Lake County, Idaho, USA).

7 pagesInternational audienceKnowledge on the morphology of Early Triassic ophiuroids is very limited, in spite of the relatively high number of described species. This hampers attempts to use morphology-based phylogenetic analyses in order to explore the early diversification of the ophiuroid modern clades between the latest Paleozoic and the early Mesozoic. Here, a new ophiuroid from the Early Triassic of southern Idaho (USA) is described and assigned to the new taxon Shoshonura brayardi Thuy nov. gen., nov. sp. It is part of an exceptional Early Triassic faunal assemblage recently described as the Paris Biota. On account of the arm morphology and the shape of the arm spines and arm spine articulations, Shoshonura brayardi nov. gen., nov. sp. is considered a basal member of the suborder Ophiodermatina

A late-surviving Triassic protomonaxonid sponge from the Paris Biota (Bear Lake County, Idaho, USA).

7 pagesInternational audienceProtomonaxonid sponges are a major group of Cambrian and Ordovician fossils in exceptionallypreserved (especially Burgess Shale-type) faunas, but are rare thereafter. Rare examples of apparentsurviving lineages are known from the late Palaeozoic and Mesozoic, but by this time more derivedgroups of sponges have generally displaced them in at least shallow-water (shelf depth) ecosystems. Theearly Spathian (Early Triassic) Paris Biota includes abundant material of a new leptomitidprotomonaxonid, Pseudoleptomitus advenus Botting nov. gen., nov. sp., distinguished by having anunbundled longitudinal skeleton and very weak transverse component. This is the first post-Ordovicianleptomitid known, and indicates long-term survival of the group in unknown environments. Itsoccurrence near storm wave base is similar to the preferred environment of earlier examples of thefamily, suggesting either ecological rarity or taphonomic reasons for their 200-million-year absencefrom later Palaeozoic rocks

Chondrichthyan teeth from the Early Triassic Paris Biota (Bear Lake County, Idaho, USA).

8 pagesInternational audienceA new, diverse and complex Early Triassic assemblage was recently discovered west of the town of Paris, Idaho (Bear Lake County), USA. This assemblage has been coined the Paris Biota. Dated earliest Spathian (i.e., early late Olenekian), the Paris Biota provides further evidence that the biotic recovery from the end-Permian mass extinction was well underway ca. 1.3 million years after the event. This assemblage includes mainly invertebrates, but also vertebrate remains such as ichthyoliths (isolated skeletal remains of fishes). Here we describe first fossils of Chondrichthyes (cartilaginous fishes) from the Paris Biota. The material is composed of isolated teeth (mostly grinding teeth) preserved on two slabs and representing two distinct taxa. Due to incomplete preservation and morphological differences to known taxa, the chondrichthyans from the Paris Biota are provisionally kept in open nomenclature, as Hybodontiformes gen. et sp. indet. A and Hybodontiformes gen. et sp. indet. B, respectively. The present study adds a new occurrence to the chondrichthyan fossil record of the marine Early Triassic western USA Basin, from where other isolated teeth (Omanoselache, other Hybodontiformes) as well as fin spines of Nemacanthus (Neoselachii) and Pyknotylacanthus (Ctenachanthoidea) and denticles have been described previously