No abstract

The dentitions of extant fishes and land vertebrates vary in both pattern and type of tooth replacement. It has been argued that the common ancestral condition likely resembles the nonmarginal, radially arranged tooth files of arthrodires, an early group of armoured fishes. We used synchrotron microtomography to describe the fossil dentitions of so-called acanthothoracids, the most phylogenetically basal jawed vertebrates with teeth, belonging to the genera Radotina, Kosoraspis, and Tlamaspis (from the Early Devonian of the Czech Republic). Their dentitions differ fundamentally from those of arthrodires; they are marginal, carried by a cheekbone or a series of short dermal bones along the jaw edges, and teeth are added lingually as is the case in many chondrichthyans (cartilaginous fishes) and osteichthyans (bony fishes and tetrapods). We propose these characteristics as ancestral for all jawed vertebrates.

Despite being known for over 155 years, the Late Cretaceous marine amniotes of the Bohemian Cretaceous Basin in the Czech Republic have received little recent attention. These fossils are however significant because they record a diverse range of taxa from an incompletely known geological interval: the Turonian. The presently identifiable remains include isolated bones and teeth, together with a few disarticulated skeletons. The most productive stratigraphical unit is the Lower–Middle Turonian Bílá Hora Formation, which has yielded small dermochelyoid sea turtles, a possible polycotylid plesiosaur and elements compatible with the giant predatory pliosauromorphPolyptychodon. A huge protostegid, together with an enigmatic cheloniid-like turtle,Polyptychodon-like dentigerous components, an elasmosaurid and a tethysaurine mosasauroid have also been found in strata corresponding to the Middle–Upper Turonian Jizera Formation and Upper Turonian – Coniacian Teplice Formation. The compositional character of the Bohemian Cretaceous Basin fauna is compatible with coeval assemblages from elsewhere along the peri-Tethyan shelf of Europe, and incorporates the globally terminal Middle–Upper Turonian occurrence of pliosauromorph megacarnivores, which were seemingly replaced by mosasauroids later in the Cretaceous.

No abstract

No abstract