Environmental control on shell size of Middle Triassic bivalve Plagiostoma.-Carnets Geol

Abstract: Fossil shells of the marine bivalve Plagiostoma striatum SCHLOTHEIM sampled from the Middle Triassic (so-called Muschelkalk) of Poland demonstrate that, under unfavourable environmental conditions, this species commonly occurring in Triassic German basins exhibits a dwarfed shell. As a consequence of a marine regression episode resulting in a significant increase of salinity and a partial emersion of seafloor these bivalves vanished. The next transgressive pulse caused a re-emergence of these bivalves. They were initially characterized by half-size shells than in the population living prior to the regression episode and, subsequently, during progressive transgression, their shells returned to normal size. Coincidence between eustatic curve and changes in bivalve shell size and their disappearance may be attributed also to biotic interactions, such as a biotic collapse in primary bioproductivity or/and a competition for space or any other resources due to shelf habitat loss during regressive periods. Résumé : Contrôle environnemental de la taille des coquilles chez Plagiostoma, un bivalve du Trias moyen.-Des coquilles fossiles du bivalve marin Plagiostoma striatum SCHLOTHEIM échantillonnées dans le Trias moyen (communément appelé Muschelkalk) de Pologne montrent que, dans des conditions environnementales défavorables, cette espèce courante dans les bassins du Trias germanique présente une taille réduite. Suite à un épisode régressif marin s'exprimant par une augmentation significative de la salinité et une exondation partielle de la partie proximale de la plate-forme et des environnements les moins profonds, ce lamellibranche disparaît. Initialement caractérisées par une taille réduite de moitié par rapport aux populations antérieures à l'épisode régressif, par la suite, leurs coquilles reviennent à une taille normale progressivement au cours de la transgression suivante. La corrélation entre la courbe eustatique et les changements de taille de la coquille de ces bivalves (et leur disparition) peut être égale-ment attribuée à des interactions biotiques, telles qu'un effondrement de la productivité biologique primaire et/ou à une compétition pour l'espace trophique ou pour toute autre ressource liée à une perte d'habitat sur la plate-forme lors de périodes régressives

The earliest bird-line archosaurs and the assembly of the dinosaur body plan

© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.The relationship between dinosaurs and other reptiles is well established, but the sequence of acquisition of dinosaurian features has been obscured by the scarcity of fossils with transitional morphologies. The closest extinct relatives of dinosaurs either have highly derived morphologies or are known from poorly preserved or incomplete material. Here we describe one of the stratigraphically lowest and phylogenetically earliest members of the avian stem lineage (Avemetatarsalia), Teleocrater rhadinus gen. et sp. nov., from the Middle Triassic epoch. The anatomy of T. rhadinus provides key information that unites several enigmatic taxa from across Pangaea into a previously unrecognized clade, Aphanosauria. This clade is the sister taxon of Ornithodira (pterosaurs and birds) and shortens the ghost lineage inferred at the base of Avemetatarsalia. We demonstrate that several anatomical features long thought to characterize Dinosauria and dinosauriforms evolved much earlier, soon after the bird-crocodylian split, and that the earliest avemetatarsalians retained the crocodylian-like ankle morphology and hindlimb proportions of stem archosaurs and early pseudosuchians. Early avemetatarsalians were substantially more species-rich, widely geographically distributed and morphologically diverse than previously recognized. Moreover, several early dinosauromorphs that were previously used as models to understand dinosaur origins may represent specialized forms rather than the ancestral avemetatarsalian morphology

Possible hominin footprints from the late Miocene (c. 5.7 Ma) of Crete?

© 2017 The Geologists' Association. We describe late Miocene tetrapod footprints (tracks) from the Trachilos locality in western Crete (Greece), which show hominin-like characteristics. They occur in an emergent horizon within an otherwise marginal marine succession of Messinian age (latest Miocene), dated to approximately 5.7 Ma (million years), just prior to the Messinian Salinity Crisis. The tracks indicate that the trackmaker lacked claws, and was bipedal, plantigrade, pentadactyl and strongly entaxonic. The impression of the large and non-divergent first digit (hallux) has a narrow neck and bulbous asymmetrical distal pad. The lateral digit impressions become progressively smaller so that the digital region as a whole is strongly asymmetrical. A large, rounded ball impression is associated with the hallux. Morphometric analysis shows the footprints to have outlines that are distinct from modern non-hominin primates and resemble those of hominins. The interpretation of these footprints is potentially controversial. The print morphology suggests that the trackmaker was a basal member of the clade Hominini, but as Crete is some distance outside the known geographical range of pre-Pleistocene hominins we must also entertain the possibility that they represent a hitherto unknown late Miocene primate that convergently evolved human-like foot anatomy

Trackways Produced by Lungfish During Terrestrial Locomotion

Some primarily aquatic vertebrates make brief forays onto land, creating traces as they do. A lack of studies on aquatic trackmakers raises the possibility that such traces may be ignored or misidentified in the fossil record. Several terrestrial Actinopterygian and Sarcopterygian species have previously been proposed as possible models for ancestral tetrapod locomotion, despite extant fishes being quite distinct from Devonian fishes, both morphologically and phylogenetically. Although locomotion has been well-studied in some of these taxa, trackway production has not. We recorded terrestrial locomotion of a 35 cm African lungfish (Protopterus annectens; Dipnoi: Sarcopterygii) on compliant sediment. Terrestrial movement in the lungfish is accomplished by planting the head and then pivoting the trunk. Impressions are formed where the head impacts the substrate, while the body and fins produce few traces. The head leaves a series of alternating left-right impressions, where each impact can appear as two separate semi-circular impressions created by the upper and lower jaws, bearing some similarity to fossil traces interpreted as footprints. Further studies of trackways of extant terrestrial fishes are necessary to understand the behavioural repertoire that may be represented in the fossil track record

Morphology of the earliest reconstructable tetrapod Parmastega aelidae.

The known diversity of tetrapods of the Devonian period has increased markedly in recent decades, but their fossil record consists mostly of tantalizing fragments1-15. The framework for interpreting the morphology and palaeobiology of Devonian tetrapods is dominated by the near complete fossils of Ichthyostega and Acanthostega; the less complete, but partly reconstructable, Ventastega and Tulerpeton have supporting roles2,4,16-34. All four of these genera date to the late Famennian age (about 365-359 million years ago)-they are 10 million years younger than the earliest known tetrapod fragments5,10, and nearly 30 million years younger than the oldest known tetrapod footprints35. Here we describe Parmastega aelidae gen. et sp. nov., a tetrapod from Russia dated to the earliest Famennian age (about 372 million years ago), represented by three-dimensional material that enables the reconstruction of the skull and shoulder girdle. The raised orbits, lateral line canals and weakly ossified postcranial skeleton of P. aelidae suggest a largely aquatic, surface-cruising animal. In Bayesian and parsimony-based phylogenetic analyses, the majority of trees place Parmastega as a sister group to all other tetrapods

The trace fossil Lepidenteron lewesiensis: a taphonomic window on diversity of Late Cretaceous fishes

The trace fossil Lepidenteron lewesiensis (Mantell 1822) provides an exceptional taphonomic window to diversity of fishes as shown for the Upper Cretaceous of Poland, in the Middle Turonian–Lower Maastrichtian deposits of the Opole Trough, Miechów Trough, Mazury-Podlasie Homocline, and SE part of the Border Synclinorium. Lepidenteron lewesiensis is an unbranched burrow lined with small fish scales and bones, without a constructed wall. It contains scales, vertebrae, and bones of the head belonging to ten taxa of teleostean fishes: two undetermined teleosteans, six undetermined Clupeocephala, one Dercetidae, and one undetermined euteleostean. The preservation of fish remains suggests that fishes were pulled down into the burrow by an animal, probably by eunicid polychaetes.Das Spurenfossil Lepidenteron lewesiensis (Mantell 1822) ermöglicht einen biostratinomischen Einblick in die Diversität von Fischen, wie Fossilmaterial aus der Oberkreide von Polen zeigt. Es stammt aus dem Mittelturonium bis Untermaastrichtium des südöstlichen Abschnittes der Grenz-Synklinale, dem Opolen-Trog, dem Miechów-Trog und der Masuren-Podlachien-Homoklinale. L. lewesiensis ist ein unverzweigter Grabgang ohne ausgekleidete Wände, dessen Ränder von kleinen Fischschuppen und—knochen gebildet werden. Diese setzen sich aus Schuppen, Wirbel und Schädelknochen von zehn Teleostei-Taxa zusammen und zwar aus zwei unbestimmte Teleosteer, sechs unbestimmten Clupeocephala, einem Dercetidae und einem unbestimmten Euteleostei. Die Erhaltung der Fischüberreste deutet darauf hin, dass die Fische von einem Tier, wahrscheinlich einem Polychaeten der Familie Eunicidae, in den Bau gezogen wurden.We are very grateful to Dr. Lionel Cavin (Geneva) and the anonymous reviewer for constructive comments on an earlier version of the manuscript. Additional support was provided by the Jagiellonian University (DS funds), National Science Center (Grant Number: PRO-2011/01/N/ST10/07717), and the Laboratory of Geology (University of Lodz) BSt Grant No. 560/844. We are grateful to Dr. Johann Egger (Wien) and Kilian Eichenseer M.Sc. (Erlangen) for help with translating the abstract into German. We are grateful to Dr. Ursula Göhlich (Wien) for access to the Dercetis specimen

Revision of stratigraphic ranges of selected invertebrate taxa from the Muschelkalk in Silesia

New occurrences of some invertebrates in the Silesian Muschelkalk are presented, hanging the stratigraphic ranges of these taxa, especially in the Dziewkowice Formation. 13 taxa have been found for the first time in this formation or had their stratigraphic ranges revised in the last two decades

An explanation for low endemism of Triassic crinoids fromthe epicontinental Germanic Basin, Poland

A summary of known crinoid taxa in the Polish part of the Triassic Germanic Basin, including their presence elsewhere, is documented. At present, 13 taxa and 3 ecophenotypes of crinoids have been recorded from that area, only one of them being endemic. In the Lower Muschelkalk and lower part of theMiddleMuschelkalk, taxa widespread both in the Tethys and Germanic Basin, or Tethyan taxa, dominate. In the Upper Muschelkalk crinoids are very rare in Poland, being represented by Encrinus liliiformis and Holocrinus sp. Many of the species occurring in the central part of the Germanic Basin in the Upper Muschelkalk have not been recorded in the eastern part of the basin. The degree of endemism of the crinoid fauna in theMuschelkalk is markedly lower than the degree of endemism of the rest of the benthonic macrofauna. This probably resulted from huge number of crinoids forming "crinoid gardens" that produced large number of larvae, increasing the chances of successful geographical expansion of crinoids