Convergent Evolution in Aquatic Tetrapods: Insights from an Exceptional Fossil Mosasaur

Mosasaurs (family Mosasauridae) are a diverse group of secondarily aquatic lizards that radiated into marine environments during the Late Cretaceous (98–65 million years ago). For the most part, they have been considered to be simple anguilliform swimmers – i.e., their propulsive force was generated by means of lateral undulations incorporating the greater part of the body – with unremarkable, dorsoventrally narrow tails and long, lizard-like bodies. Convergence with the specialized fusiform body shape and inferred carangiform locomotory style (in which only a portion of the posterior body participates in the thrust-producing flexure) of ichthyosaurs and metriorhynchid crocodyliform reptiles, along with cetaceans, has so far only been recognized in Plotosaurus, the most highly derived member of the Mosasauridae. Here we report on an exceptionally complete specimen (LACM 128319) of the moderately derived genus Platecarpus that preserves soft tissues and anatomical details (e.g., large portions of integument, a partial body outline, putative skin color markings, a downturned tail, branching bronchial tubes, and probable visceral traces) to an extent that has never been seen previously in any mosasaur. Our study demonstrates that a streamlined body plan and crescent-shaped caudal fin were already well established in Platecarpus, a taxon that preceded Plotosaurus by 20 million years. These new data expand our understanding of convergent evolution among marine reptiles, and provide insights into their evolution's tempo and mode

Remarks on the origin of cerussite in the Upper Silesian Zn-Pb deposits, Poland

Cerussite, the most important oxidized lead mineral in the Upper Silesian Zn-Pb deposits, occurs in two readily distinct types: fine-grained cerussite replacing galena in-situ and macrocrystalline cerussite filling open fractures and cavities. Microscopic observations and thermodynamic considerations lead to the conclusion that galena can be oxidized to lead carbonate directly, not necessarily through an intermediate sulphate phase. Locally present iron sulphides undergoing oxidation acidify solutions and provide ferric ions which are important oxidizing agents. In such microenvironments, anglesite can preferentially form. Cerussite and galena commonly coexist together with non-oxidized zinc sulphides. It is difficult to explain such assemblages if galvanic couplings made of these two sulphides are not considered. These couplings are only formed when these two sulphides are in direct contact. In such an assemblage, galena undergoes oxidation, mostly to cerussite, and sphalerite is passivated. When there is no direct contact between sulphides, the galvanic couplings do not exist. Galena surfaces become covered by oxidation products which inhibit further oxidation. As such a cover does not form on sphalerite, it can be easily oxidized

Pyrite framboids in pyritized Radiolarian skeletons (Mid-Cretaceous of the Pieniny Klippen Belt, Western Carpathians, Poland)

Well preserved pyritized radiolarian skeletons have been found within the grey-green Mid-Cretaceous (Upper Cenomanian) shales in the Pieniny Klippen Belt (Carpathians, Poland). The skeletons contain numerous pyrite framboids in different positions, in channels and inside the abdomen of cryptothoracic forms, but their genetic context is not known. They were formed as a result of the reaction between dissolved iron and sulphide originated from the bacterial sulphate reduction. Two sources of organic matter, "post mortem" in situ decaying organic matter of radiolaria and disseminated organic matter from the surrounding sediment could be available for this process. Pyrite found in the radiolarians probably originates from different processes. It is suggested that pyritization of the radiolarian skeletons took place in the water column whereas pyrite framboids in the skeleton's free spaces could have been formed later during the diagenesis of the sediment. However, their simultaneous formation in the water column or in the sediment cannot be excluded

Mineralogical and geochemical characteristics of the iron corrosion products from the Wieliczka Salt Mine

Korozja jest to proces stopniowego fizykochemicznego niszczenia metali pod wpływem działania środowiska otaczającego (przeważnie ciekłego i gazowego). Jednym z nich jest środowisko o podwyższonych zasoleniu, w którym proces ten zachodzi wyjątkowo szybko. Próbki do badań zostały pobrane w czasie kilku zjazdów do Kopalni Soli "Wieliczka". Były to różne metalowe fragmenty (rury, łańcuch, zawory). Makroskopowo zaobserwowano, że pobrane próbki uległy korozji w różnym stopniu: częściowo lub całkowicie. W próbkach, które uległy korozji całkowicie wydzielono dwie główne jej warstwy (warstwę zewnętrzną "A" oraz wewnętrzną "B"). Każda warstwa następnie została podzielona na dwie podwarstwy. Dodatkowo wyróżniono czarne pęcherze, które powstały głównie na fragmencie łańcucha. Wykonane badania XRD wykazały, że minerały budujące poszczególne warstwy to: akaganeit, hematyt, goethyt, halit, lepidokrokit oraz magnetyt. Skład mineralny poszczególnych warstw w znacznym stopniu wpływa na ich zabarwienie. W mikroskopie skaningowym z systemem analitycznym EDS wyróżniono w warstwach różne formy morfologiczne o zróżnicowanym składzie chemicznym.Corrosion is a process of physico-chemical destruction of metals under the influence of surrounding environment. In a salt mine, where the salinity of air and water is high, the destruction is very fast and efficient. Metal fragments (pipes, chain), at different progress of corrosion, were collected underground in the Wieliczka Salt Mine. Two main layers of corrosion were distinguished (external "A" and internal "B"), each of them was further subdivided into two sublayers. In addition, black blebs, present on the surface of different metal fragments, were studied. XRD determinations showed that the studied layers were composed of different amounts of: akaganeite, hematite, goethite, halite, magnetite, and subordinate amounts of lepidocrockite. The mineral composition greatly affects the color of the layers. SEM-EDS studies revealed various morphological forms of different chemical composition

Geochemistry of Middle Jurassic mudstones (Kraków-Częstochowa area, southern Poland): interpretation of the depositional redox conditions

Middle Bathonian iron-bearing dark grey mdstones and claystones from the Kraków-Czestochowa Upland (southern Poland) were subjected to geochemical and mineralogical study in order to evaluate palaeo-redox conditions of their deposition and diagenesis. They are mainly composed of kaolinite, with smaller amounts of other clay minerals and detrital quartz. Organic matter is composed of type III and/or IV kerogen and its d13C is between -23 and -24‰, suggesting a mainly terrigenous source, with a possible admixture of marine input. Most geochemical parameters: (total organic carbon) TOC/S, U/Th, Ni/Co, V/Cr, (Cu+Mo)/Zn ratios, authigenic uranium content, and Fe-TOC-S relationship, indicate deposition under oxygenated bottom water conditions. By contrast, DOP (degree of pyritization) and V/V+Ni indices suggest a dysoxic environment. However, DOP probably reflects redox conditions in the sediment during diagenesis rather than in the over laying water column. The composition of the organic matter and the domination of pyrite euhedra over framboids indicates that the V/V+Ni ratio may not be reliable for determination of redox conditions in the rocks studied. There is no significant difference between the geochemical indices of host rocks with nodules and those with out them