Martin Mazuch

Boreal-tethyan correlation of the Jurassic-Cretaceous boundary interval by magneto- and biostratigraphy

As a result of detail sampling and paleomagnetic study of the 27-m-thick section of Jurassic-Cretaceous boundary beds in the Nordvik Peninsula (Anabar Bay, Laptev Sea), a succession of M-zones correlative with chrons M20n-M17r is established for the first time in the Boreal deposits. Inside the normal polarity zone corresponding to Chron M20n, a thin interval of reversed polarity, presumably an equivalent of the Kysuca Subzone (M20n.1r), is discovered. The other thin interval of reversed polarity established within the next normal polarity zone (M19n) is correlated with the Brodno Subzone (M19n.1r). The same succession of normal and reversed polarity zones has been discovered recently in the Jurassic-Cretaceous boundary beds of the Tethyan sections: in the Bosso Valley (Italy), at the Brodno (Slovak Republic) and Puerto Escaño (Spain) sites. Correlation of successions established lead us to conclusion, that the Jurassic-Cretaceous boundary corresponds in the Panboreal Superrealm to a level within the Craspedites taimyrensis Zone of the upper Volgian Substage. Hence, the greatest part of Volgian Stage should be included into the Jurassic System. Biostratigraphic data do not contradict this conclusion.

Palaeoenvironments and palaeoceanography changes across the Jurassic/Cretaceous boundary in the Arctic realm: case study of the Nordvik section (north Siberia, Russia)

The Jurassic/Cretaceous transition was accompanied by significant changes in palaeoceanography and palaeoenvironments in the Tethyan Realm, but outside the Tethys such data are very scarce. Here we present results of a study of the most complete section in the Panboreal Superrealm, the Nordvik section. Belemnite δ18O data show an irregular decrease from values reaching up to +1.6‰ in the Middle Oxfordian and from +0.8 to −1.7‰ in the basal Ryazanian, indicating a prolonged warming. The biodiversity changes were strongly related to sea-level oscillations, showing a relatively low belemnite and high ammonite diversity during sea-level rise, accompanied by a decrease of the macrobenthos taxonomical richness. The most prominent sea-level rise is marked by the occurrence of open sea ammonites with Pacific affinities. Peak abundances of spores and prasinophytes correlate with a negative excursion in organic carbon δ13C near the J/K boundary and could reflect blooms of green algae caused by disturbance of the marine ecosystem.

Evidence for fish predation on a coleoid cephalopod from the Lower Jurassic Posidonia Shale of Germany

A specimen of the Early Jurassic actinopterygian fish Pachycormus sp. from the Lower Jurassic Posidonia Shale of Germany has a well preserved filling of the alimentary canal. The region interpreted as the stomach contains numerous hooklets that can be referred to the coleoid cephalopod Phragmoteuthis Mojsisovics, 1882. The presence of arm hooklets clearly demonstrates predation on coleoid cephalopods by actinopterygian fishes.

A basal ornithopod dinosaur from the Cenomanian of the Czech Republic

During their long evolutionary history, neornithischian dinosaurs diverged into several clades with distinctive adaptations. However, the early evolution within Neornithischia and the resolution of the phylogenetic relationships of taxa situated near the base of the clade remain problematic. This is especially true for those taxa traditionally placed at the base of Ornithopoda, either as ‘hypsilophodontids’ or at the base of the diverse clade Iguanodontia. Recent studies are improving our understanding of the anatomy and relationships of these taxa, with discoveries of several new non-ankylopollexian ornithopods from South America and Europe providing key insights into early ornithopod evolution and palaeobiogeography. Here, we describe a new basal ornithopod, Burianosaurus augustai gen. et sp. nov., based on a well-preserved femur from the upper Cenomanian strata (Korycany Beds of the Peruc-Korycany Formation) of the Czech Republic. The new taxon is diagnosed by a unique suite of characters and represents the only occurrence of a Cenomanian non-avian dinosaur in Central Europe north of the Alpine Tethyan areas. Histological examination of the type specimen reveals the presence of a loosely packed Haversian system which suggests relatively mature bone from a possible young adult. Phylogenetic analyses of two different data sets, selected to test the placement of B. augustai in various parts of the neornithischian tree, reconstruct B. augustai as a basal ornithopod, firmly nested outside Ankylopollexia. These results also support a diverse Elasmaria as a basal clade within Ornithopoda and reconstruct Hypsilophodon outside Ornithopoda as the sister taxon to Cerapoda. However, the relationships of ‘hypsilophodontids’ within Neornithischia remain contentious. http://zoobank.org/urn:lsid:zoobank.org:pub:D28A9FB8-A253-4032-8710-4F51668A1E4F