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Avascular necrosis, diagnosed on the basis of either a specific pathological modification of the articular surfaces of bone or its radiologic appearance in vertebral centra, has been recognized in many Mesozoic marine reptiles as well as in present-day marine mammals. Its presence in the zoological and paleontologic record is usually associated with decompression syndrome, a disease that affects secondarily aquatic vertebrates that could dive. Bone necrosis can also be caused by infectious processes, but it differs in appearance from decompression syndrome-associated aseptic necrosis. Herein, we report evidence of septic necrosis in the proximal articular surface of the femur of a marine reptile, Pistosaurus longaevus , from the Middle Triassic of Poland and Germany. This is the oldest recognition of septic necrosis associated with septic arthritis in the fossil record so far, and the mineralogical composition of pathologically altered bone is described herein in detail. The occurrence of septic necrosis is contrasted with decompression syndrome-associated avascular necrosis, also described in Pistosaurus longaevus bone from Middle Triassic of Germany.

The Middle Triassic fossil reptile localities near Bayreuth (Bavaria, southern Germany) consist of shallow marine autochthonous glauconitic marls and terebratulid-rich tempestite carbonates of the newly defined Bindlach and Hegnabrunn formations. Single bones and incomplete skeletons of marine reptiles have been recorded in bone beds within in the Illyrian and Fassanian stages. These include the remains of the sauropterygians Neusticosaurus sp., Lariosaurus cf. buzzii [1], Nothosaurus mirabilis [2], Paranothosaurus giganteus [2], Placodus gigas [3], Cyamodus rostratus [4], Cyamodus münsteri [5], Pistosaurus longaevus [6], and ichthyosaursOmphalosaurus sp., and Shastasaurus sp. or proterosaur Tanystrophaeus conspicuus [7]. New skeletal reconstructions are based on the osteological analysis of three dimensionally preserved bones and skeletal remains. The large number of marine endemic placodont macroalgae feeders (P. gigas) in the Bayreuth sites coincides with the presence of invertebrate palaeocommunities that are characteristic of macroalgae meadow paleoenvironments. Most of the reptile species and genera from the Bayreuth localities also occur in beds of similar ages from the Monte San Giorgio (Switzerland/Italy) or Perledo (Italy) lagoonal areas. Ichthyosaurs and pistosaurs were adapted for open marine conditions, and may have migrated from the Panthalassa Oceans into the shallow marine Germanic Basin to reproduce, whereas placodonts and many other sauropterygians seem to have lived permanently in those shallow marine habitats, with large squamates and thecodont or smaller archosaurs in coastal areas.

More than seventy-five vertebrate track-sites have been found in Central Europe in 243–246.5 m.y. old Triassic coastal intertidal to sabkha carbonates. In the western part of the very flat Triassic intracontinental Germanic Basin, the carbonate strata contain at least 22 laterally extensive track horizons (called megatracksites). In contrast, in the eastern part of the basin only six megatracksites extended to near the centre of the Basin during marine low stands. Marine ingression and the development of extensive coastal marine environments began during the Aegean (Anisian) stage. This incursion began in the region of the eastern Carpathian and Silesian gates and spread westward due to the development of a tectonically controlled intracratonic basin. The tectonic origin of this basin made it susceptible to tsunamis and submarine earthquakes, which constituted very dangerous hazards for coastal terrestrial and even marine reptiles. The shallow sea that spread across the Germanic Basin produced extensive tidal flats that at times formed extensive inter-peninsular bridges between the Rhenish and Bohemian Massifs. The presence of these inter-peninsular bridges explains the observed distribution and movement of reptiles along coastal Europe and the northern Tethys Seaway during the Middle Triassic epoch. Two small reptiles, probably Macrocnemus and Hescherleria , left millions of tracks and trackways known as Rhynchosauroides and Procolophonichnium in the Middle Triassic coastal intertidal zone. The great abundance of their tracks indicates that their trackmakers Macrocnemus and Hescherleria were permanent inhabitants of this environment. In sharp contrast, tracks of other large terrestrial reptiles are quite rare along the coastal margins of the Germanic Basin, for example the recently discovered archaeosaur tracks and trackways referable to Isochirotherium , which most probably were made by the carnivore Ticinosuchus . Smaller medium-sized predatory thecodont reptiles, possibly Euparkeria , probably made the Brachychirotherium trackways that have been found across much of Central Europe. Large lepidosaurs such as Tanystrophaeus probably hunted in the tidal ponds and channels, where they locally produced Synaptichnium tracks. Recently discovered tracks made by a basal prosauropod are the world's oldest record of this group of dinosaurs, occurring in beds that have an age of about 243.5 Ma. (Pelsonian substage). This shows that very large prosauropods existed much earlier than was previously believed. These prosauropod tracks, along with tracks of small bipedal dinosaurs found in the Alps and Eastern France, show that by the middle part of the Middle Triassic the radiation and diversification of dinosaurs was already in progress. In the Germanic Basin, aquatic-adapted paraxial swimming sauropterygians are not known to have left tracks, except for occasional subaquatic swimming scratch-mark “trackways” within the coastal tidal flat zone. Marine-adapted aquatic reptiles migrated into the Germanic Basin with increasing frequency in the upper part of the Middle Triassic, when the bathymetry of the Germanic Basin was at its deepest following a strong regression that occurred due to basin uplift in the middle part of the Middle Triassic. These large marine reptiles included Pistosaurus , the ichthyosaurs Cymbospondylus or Mixosaurus , and many placodonts such as Cyamodus , Placodus and Paraplacodus , which fed on macroalgae and seem to have been the Triassic sea cows of their day. The distribution of these reptiles was mainly controlled by tectonics, but eustatic changes in sea level also were important and produced widespread environmental changes across the tidal flats up until their disappearance in the Germanic Basin in the late Middle Triassic. The initial break-up of Pangaea already had started in Middle Triassic time, and this event had begun to drastically change environments all over Central Europe. It is very interesting that dinosaurs began to diversify at exactly this time, and it seems likely that this was a direct reaction to these environmental changes. It can be inferred that the earliest dinosaurs must have started to evolve in the late Early Triassic, because in Europe it can be demonstrated that at least two main dinosaur groups already were present and clearly differentiated by the middle part of the Middle Triassic, and all three of the major groups of dinosaurs (theropods, sauropods and ornithischians) had diversified and spread globally throughout terrestrial habitats by the end of the Triassic Period. Six new palaeogeographic maps, representing time intervals from the Aegean to the Illyrian (Anisian) stages, show these important environmental changes in detail and explain the direction and timing of terrestrial reptile exchanges between the Central Massif, Rhenish Massif, and Bohemian Massif, and also the direction and timing of marine reptile exchanges between the Alps of Central Pangaea and the ancient northern Tethys Ocean and Germanic Basin Sea.

The skull of Augustasaurus hagdorni from the Middle Triassic of northwestern Nevada is described in detail, and compared to those of Pistosaurus and Plesiosaurus. New information amends the earlier description of the postcranial skeleton of Augustasaurus. Phylogenetic analysis corroborates the sister-group relationship of Augustasaurus and Pistosaurus. These two taxa form a clade that is the sister-group of Plesiosaurus. The paleobiogeographical implication of the sister-group relationship of Augustasaurus and Pistosaurus is discussed and linked to the exotic terrane model.

A new sauropterygian, Anshunsaurus huangguoshuensis, is described on the basis of a well-preserved skull from the Late Triassic Wayao Member of Falang Formation, Guizhou Province, southwestern China. It is ascribed to Eusauropterygia because it possesses the following characters: the rostrum is mainly composed by the premaxillae; the nasals are small, paired and separated from one another by the premaxillae; the external nares are close to the orbits; and the frontals are fused. Anshunsaurus differs from other Triassic sauropterygians in its large size, long rostrum and the supratemporal fenestrae slightly smaller than orbits. It is further considered to be closely related to Pistosaurus on the basis of the nasals contact with the prefrontals; large pineal foramen, lain in the anterior part of the parietal table; the squamosals not in contact posterior to the supratemporal fenestra. The discovery of Anshunsaurus with the ichthyosaurs in the same locality indicates a new assemblage of Triassic marine tetrapods in China.

The holotype and other material of Corosaurus alcovensis Case from the Alcova Limestone of Casper, Wyoming, was further prepared using a combination of chemical techniques. Anatomical revision resulted in the definition of new characters for the analysis of the phylogenetic interrelationships of Triassic stem-group Sauropterygia that document paraphyly of the Eusauropterygia. Corosaurus is the sister-taxon to a clade comprising Cymatosaurus, Pistosaurus , and by extension, plesiosaurs and pliosaurs.

We describe a new pistosaurid sauropterygian, Augustasaurus hagdorni, gen. et sp. nov., from the Middle Triassic of Nevada. The specimen was collected in Muller Canyon, Augusta Mountains, from a late Anisian laminated mudstone unit in the Fossil Hill Member of the Favret Formation. Augustasaurus hagdorni is based on a partial articulated skeleton consisting of the posterior neck, trunk, shoulder girdle, and both forelimbs. In comparison to Pistosaurus from the Muschelkalk Beds of central Europe, the neural spines of the new pistosaurid are lower and longer with autapomorphic saw-cut rugosities and double facets of unfinished bone. Augustasaurus hagdorni has reduced front limbs with relatively short distal elements and a phalangeal formula of 1-1-3-3-1. This condition is very different from that in plesiosaurs, the presumed sister-group of pistosaurids.

Background Eosauropterygians consist of two major clades, the Nothosauroidea of the Tethysian Middle Triassic (e.g., Nothosaurus) and the Pistosauroidea. The Pistosauroidea include rare Triassic forms (Pistosauridae) and the Plesiosauria of the Jurassic and Cretaceous. Long bones of Nothosaurus and Pistosaurus from the Muschelkalk (Middle Triassic) of Germany and France and a femur of the Lower Jurassic Plesiosaurus dolichodeirus were studied histologically and microanatomically to understand the evolution of locomotory adaptations, patterns of growth and life history in these two lineages. Results We found that the cortex of adult Nothosaurus long bones consists of lamellar zonal bone. Large Upper Muschelkalk humeri of large-bodied Nothosaurus mirabilis and N. giganteus differ from the small Lower Muschelkalk (Nothosaurus marchicus/N. winterswijkensis) humeri by a striking microanatomical specialization for aquatic tetrapods: the medullary cavity is much enlarged and the cortex is reduced to a few millimeters in thickness. Unexpectedly, the humeri of Pistosaurus consist of continuously deposited, radially vascularized fibrolamellar bone tissue like in the Plesiosaurus sample. Plesiosaurus shows intense Haversian remodeling, which has never been described in Triassic sauropterygians. Conclusions The generally lamellar zonal bone tissue of nothosaur long bones indicates a low growth rate and suggests a low basal metabolic rate. The large triangular cross section of large-bodied Nothosaurus from the Upper Muschelkalk with their large medullary region evolved to withstand high bending loads. Nothosaurus humerus morphology and microanatomy indicates the evolution of paraxial front limb propulsion in the Middle Triassic, well before its convergent evolution in the Plesiosauria in the latest Triassic. Fibrolamellar bone tissue, as found in Pistosaurus and Plesiosaurus, suggests a high growth rate and basal metabolic rate. The presence of fibrolamellar bone tissue in Pistosaurus suggests that these features had already evolved in the Pistosauroidea by the Middle Triassic, well before the plesiosaurs radiated. Together with a relatively large body size, a high basal metabolic rate probably was the key to the invasion of the Pistosauroidea of the pelagic habitat in the Middle Triassic and the success of the Plesiosauria in the Jurassic and Cretaceous.

"Pistosaurus from upper part of middle Triassic in southern Germany is the earliest plesiosaur of which a complete restoration can be given; it still has long legs, not yet ordinary paddles."