Els mol·luscs terrestres fòssils de les Illes Pitiüses

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Enodicalix (Diploporita, Aristocystitidae): A new echinoderm genus from the Middle Ordovician of Spain

Restudy of an Ordovician diploporite specimen from the Middle Ordovician of central Spain reveals that the species ‘Calix’ inornatus MELÉNDEZ has four ambulacra, each with two equal facets, an oval hydropore and a smooth thecal surface. In contrast, the type species of Calix has four ambulacra, each with four facets added in a clockwise direction during growth, a trilobed hydropore, and a theca with spiny plates. Other aristocystitid genera with four ambulacra have one facet per ambulacrum. ‘Calix’ inornatus differs from all other aristocystitid genera and warrants a new generic name, for which we propose Enodicalix.

New insights into the origin and relationships of blastoid echinoderms

“Pan-dichoporites” (new informal term) is proposed to unite Cambrian blastozoans, such as Cambrocrinus, Ridersia, and Sanducystis, glyptocystitoid and hemicosmitoid rhombiferans, coronates, blastoids, and Lysocystites. Pan-dichoporite ambulacra have double biserial main axes with brachiole facets shared by pairs of floor (glyptocystitoids), side (blastoid) or trunk (hemicosmitoids, coronates) plates. These axial plates are the first two brachiolar plates modified to form the ambulacral axes. In glyptocystitoids the first brachiole facet in each ambulacrum is shared by an oral and another plate. Hence, these are also two modified brachiolar plates and part of the axial skeleton under the Extraxial Axial Theory (EAT). Pan-dichoporites are also characterized by thecae composed of homologous plate circlets. The unique glyptocystitoid genus Rhombifera bears ambulacral facets on five radial plates, which alternate with five orals. The oral area of Lysocystites (blastoid sensu lato) is very similar, which suggests that rhombiferan radials are homologous with “ambulacrals” of Lysocystites and hence with blastoid lancet plates. This implies derivation of blastoids from glyptocystitoids and suggests that blastoid and coronate radials and deltoids are homologous with rhombiferan infralaterals and laterals. Thus, homologous plate circlets occur in all pan-dichoporites, which strengthens the validity of a pan-dichoporite clade. Under Universal Elemental Homology (UEH), deltoids were homologized with rhombiferan orals, but this is inconsistent with the EAT. Deltoids bear respiratory pore structures and so are perforate extraxial skeletal plates, whereas rhombiferan orals are axial skeleton. The new plate homologies also explain why only five plates form the oral frames of coronates, blastoids and Lysocystites, whereas glyptocystitoids (except Rhombifera) have six oral frame plates; all glyptocystitoids have only five laterals. Hemicosmitoids arose by paedomorphic ambulacral reduction, but the paedomorphosis also affected the thecal plates and stem. Paedomorphosis poses special problems for cladistic character analysis, since the new characters often appear to be plesiomorphic

Trace fossils

Book synopsis: The coastline of Dorset is spectacular and beautiful. It exposes a long squence of Jurassic age sedimentary rocks which, with its wealth of invertebrate, vertebrate and plant fossils, has long attracted palaeontologists amateur, professional, interested holiday–maker, dedicated collector and its international importance has been recognised by the designation as a UNESCO World Heritage Site. From the pioneering work of early collectors like Mary Anning onwards, the area has been a cradle of palaeontology. The Lower Lias is particularly fossiliferous and this lavishly illustrated Guide covers all the fossil groups to be found by the collector in the field

Late Ordovician (Hirnantian) Diploporitan Fauna of Anticosti Island, Quebec, Canada: Implications for Evolutionary and Biogeographic Patterns

Hirnantian (latest Ordovician) localities containing echinoderm fossils are rare; the few that have been discovered primarily contain disarticulated crinoid ossicles. Therefore, relatively little is known about echinoderm evolutionary dynamics across the Late Ordovician – early Silurian boundary, especially noncrinoid echinoderms. New diploporitan echinoderms, Holocystites salmoensis and an unidentified holocystitid, from reefal facies of the Upper Ordovician Ellis Bay Formation of Anticosti Island provide a critical data point concerning diploporitan biogeography and evolutionary pathways undertaken during the Ordovician and Silurian. These fossils also provide a crucial link in understanding the ancestry of the Silurian Holocystites Fauna, an unusual diploporitan fauna from the middle Silurian of North America, whose origination dates back at least 15 million years earlier than previously thought with the discovery of taxa described here. New fossil data such as these stress the importance of uncovering new localities from underrepresented times and places in Earth’s history, so that these evolutionary transitions can be better understood