Variations in Jurassic echinoid biodiversity at ammonite zone levels: Stratigraphical and palaeoecological significance

After a relatively low but stable phase of taxonomic diversity during the Lias (Lower Jurassic), echinoids diversity strongly increases from Aalenian (Dogger-Middle Jurassic) to Kimmeridgian (Malm-Late Jurassic) and a conspicuous crisis takes place in Tithonian times, before the end of the Jurassic. During these major phases, minor decreases in diversity correspond with regressions (sea-level falls), mainly in the Middle Bathonian (Middle Jurassic). From the Aalenian to Callovian, the average duration of irregular echinoid species is about 3.8 m.y. whereas it is about 5.5 m.y. for the regular ones; the later value corresponding to the average duration of a Jurassic. From Callovian to Tithon…

Paléobiosphère : regards croisés des sciences de la vie et de la Terre.

796 pages

100‐million‐year‐old ant–conifer associates inside French amber: a fortuitous or ecological association?

International audience; Ants exhibit a plethora of ecological interactions with terrestrial plants. These interactions are broadly surveyed in modern ecosystems, but are much more difficult to unveil in the fossil record. Here, we report a unique ant–conifer association preserved in an opaque piece of 100‐million‐year‐old amber from Charentes in Western France, revealed by propagation phase‐contrast X‐ray synchrotron microtomography (PPC‐SRμCT). Most legs of the ant encircle the conifer twig, and the arthropod harbours a hooked position onto the leafy axis. The conifer is assigned to Glenrosa carentonensis Moreau, Néraudeau, Tafforeau and Dépré, whereas the ant is ascribed to Gerontoformica…

Astérides du Cénomanien de Charente-Maritime (SW France)

Resume Des restes d'Asterides (plaques infero- et superomarginales) ont ete trouves dans les sediments du Cenomanien deCharente-Maritime (Sud-Ouest de la France). Ils appartiennent a 17 taxons, dont la nouvelle espece Calliderma moreaui nov. sp., et correspondent a 5 familles differentes: Goniasteridae, Pycinasteridae, Stauranderasteridae, Sphaerasteridae et Astropectinidae. Leur description est suivie d'une breve analyse de leurs repartitions stratigraphique et paleobiogeographique.

Albian flora from Archingeay-Les Nouillers (Charente-Maritime): comparison and synthesis of Cretaceous meso- and macro-remains from the Aquitaine Basin (southwestern France)

International audience; Over recent decades, diverse structures ascribed to angiosperms, bennettitaleans, conifers, cycads, ginkgophytes and pteridosperms have been reported from the Cretaceous deposits of the Aquitaine Basin (southwestern France). However, Albian macrofloras remain uncommon in Aquitania as well as in France. The clay from the Archingeay-Les Nouillers quarries is one of the rare deposits of the Aquitaine Basin to yield Albian plant meso- and macro-remains. Although Albian plant-bearing beds are not accessible any more in these quarries, samples collected from excavations conducted at the end of the XXth century were deposited in the collections of the University of Rennes 1…

New Hettangian tracks from the Causses Basin (Lozère, southern France) complement the poor fossil record of earliest Jurassic crocodylomorphs in Europe

International audience; A new vertebrate ichnological assemblage is described from the Hettangian Dolomitic Formation of the Causses Basin, at Le Serre (Lozère, southern France). We report tracks that complement the poor fossil record of lowermost Jurassic crocodylomorphs in Europe. Tetradactyl pes and pentadactyl manus imprints form a unique trackway. Traces are ascribed to Batrachopus isp. and they represent the third occurrence of this ichnogenus in European Hettangian geological formations. This is the first report of Batrachopus in Hettangian deposits of the Causses Basin. The tracks share some similarities with Batrachopus deweyi previously described from the Sinemurian of the Causses…

Tuberculation in spatangoid fascioles: Delineating plausible homologies

The existing definition of spatangoid fascioles as a narrow band of minute tubercles (miliaries) is inadequate. One reason is that many intermediates between the presence of indisputable fascioles and their total absence are known. Although fascioles are widely used in the classification of spatangoids, diversity of fasciole tuberculation has largely been ignored. We examine fascioles in about 100 spatangoid species, focusing on the earliest manifestations of fascioles (both developmentally and phylogenetically) and on their variable tuberculation. Qualitative observations are complemented by quantitative analyses (ANOVA and PCA) of 21 species. Three types of fascioles are defined according…

Conifers from the Cenomanian amber of Fouras (Charente-Maritime, western France)

Fossil inclusions of arthropods and microorganisms are abundant in the Cretaceous amber from western France, but plant meso- or macroremains are scarce. Preserved remains are mostly tiny, very fragmented, and indeterminable. Only one amber locality in the Charente department has already provided conifer remains. Here, we report the first plant mesoremains ensnared in Cenomanian amber from Fouras – Bois Vert, in the Charente-Maritime department. They consist of three well-preserved leafy axes and one cone of Cheirolepidiacean conifers. Based on the helical arrangement of rhomboidal, longer than wide, and highly adpressed leaves, leafy axes are ascribed to the genus Pagiophyllum. The ovoid co…

Biogeography and diversity of South Atlantic Cretaceous echinoids: implications for circulation patterns

Abstract This survey of echinoid species living on the African and South American margins of the South Atlantic Ocean in Cretaceous times is based on a review of published species and abundant unpublished material. The synthetic approach is used to ascertain how the South Atlantic was colonised by echinoids from the time it first opened in the Early Cretaceous until communications were established with the North Atlantic and Mediterranean–Tethys in the Late Cretaceous. The survey focuses on the biogeographical origin of immigrant species and their relations with Indo-Madagascan, North Atlantic and Mediterranean–Tethyan faunas. Qualitative variations in species diversity are also studied whe…

Le site à ambre et plantes du Cénomanien de Neau (Mayenne, France)

International audience; A new Cenomanian amber- and plant-bearing deposit has been discovered at Neau, in the Mayenne department (France). The Cenomanian fossiliferous lignites are located in karst filling in a substratum of Cambrian limestones. The amber corresponds mainly to tiny millimetric grains, devoid of arthropod inclusions, but rich in microorganisms, especially the sheated bacteria Leptotrichites resinatus , and containing pollen grains ( Classopollis ) and wood fibers (Araucariacae or Cheirolepidiaceae). The lignites provide abundant conifer and ginkgoale cuticle fragments ( Frenelopsis , Eretmophyllum ) and a lot of palynomorphs ( e.g. Gleicheniidites senonicu s, Cyathidites , D…

Tithonia oxfordiana, a new irregular echinoid associated with Jurassic seep deposits in south-east France

The infaunal irregular echinoid, Tithonia oxfordiana, is described and compared to congeneric species previously described from Upper Jurassic and lowermost Cretaceous strata. This new species characterizes a monospecific echinoid assemblage, which occurs only in some places where deep-marine middle Oxfordian deposits are exposed in south-east France. Specimens are closely packed and clearly concentrated at the top of small carbonate chemoherms; a close connection of the echinoids with the emission of reduced chemicals, which were oxidized by chemoautotrophic bacteria, is highly probable. Based on general test shape and plate architecture, T. oxfordiana probably was a deposit feeder on chem…

Transgressions‐regressions and echinoid morphoclines

Synthèse sur la diversité des préservations végétales du site d’Archingeay-Les Nouillers (France) : un Konservat-Lagerstätte pour les flores de l’Albien-Cénomanien

Since the end of the XXth century, the palaeontological site of Archingeay-Les Nouillers (Charente-Maritime, western France) continued to afford Albian-Cenomanian (ca 93–113 Ma) plant meso- and macroremains. The successive excavations provided numerous specimens useful for the reconstruction of mid-Cretaceous coastal forest ecosystems. However, one of the most remarkable features of this locality is the diversity of plant preservations. Unique in Europe from this point of view, the fossiliferous site of Archingeay-Les Nouillers yielded compressions with or without cuticle, impressions/imprints, and silicified permineralizations/petrifications. The quality of the silicified tissues and the c…

Paleohistology of the Cretaceous resin‐producing conifer Geinitzia reichenbachii using X‐ray synchrotron microtomography

International audience; PremiseThe conifer Geinitzia reichenbachii was a common member of the Cretaceous Laurasian floras. However, the histology of G. reichenbachii leafy axes was never described in detail, and our knowledge of its paleoecology remains very limited. Using new and exquisitely preserved silicified material from the Upper Cretaceous of western France, we describe G. reichenbachii from the gross morphology to the cellular scale, then discuss paleoecological and taphonomical implications.MethodsWe examined specimens from two localities in western France (Claix and Moragne) using propagation phase-contrast X-ray synchrotron microtomography.ResultsThe cuticle and the inner tissue…

Étude paléobotanique d’une lentille argileuse cénomanienne de la carrière de Hucheloup, Maine-et-Loire, NO France : implications taxonomiques, stratigraphiques et paléoenvironnementales

International audience; A Cenomanian clay lens in Hucheloup Quarry (Maine-et-Loire, north-western France) has yielded 82 foliar compressions and impressions, of which 62 were identified at several taxonomic levels. The plants are ascribed to diverse Pinales (27%), ferns (27%), Ginkgoales (26%), angiosperms (19%) and Cycadales (1%). The most abundant species in the assemblage are Frenelopsis alata (K. Feistmantel) E. Knobloch emend. J. Kvaček (Pinales) and Eretmophyllum obtusum (Velenovský) J. Kvaček (syn. E. andegavense Pons, Bourreau et Broutin) (Ginkgoales). Wood fragments, along with very well-preserved cuticles, have also been recovered and identified. The specimens are usually very fra…

Phylogeny of Early Cretaceous spatangoids (Echinodermata: Echinoidea) and taxonomic implications

A phylogenetic analysis of 36 species provides a test for the taxonomy and the history of Early Cretaceous spatangoids. Most taxonomic units from genera to suborders are consistent with the proposed phylogenetic framework. We retain Hemiasterina, Micrasterina, Hemiasteridae, Schizasteridae, Hemiaster, Heteraster, Mecaster, and Periaster as original monophyletic groups. However, all of these clades originate without the classical apomorphies normally ascribed to them. We suggest a revision of their diagnoses and of the generic attributions of basal species. Some ill-defined, ‘primitive’, and paraphyletic taxa are recognised: Toxaster, Epiaster, Palhemiaster, and Toxasteridae. Even if they do…