No abstract

The electron-donating properties of N-heterocyclic carbenes ([N,N'-bis(2,6-dimethylphenyl)imidazol]-2-ylidene and the respective dihydro ligands) with 4,4'-R-substituted aryl rings (4,4'-R=NEt2, OC(12)H(25), Me, H, Br, S(4-tolyl), SO(4-tolyl), SO2(4-tolyl)) were studied. Twelve new N-heterocyclic carbene (NHC) ligands were synthesized as well as the respective iridium complexes [IrCl(cod)(NHC)] and [IrCl(CO)2(NHC)]. Cyclic voltammetry (DeltaE1/2) and IR (nu (CO)) can be used to measure the electron-donating properties of the carbene ligands. Modifying the 4-positions with electron-withdrawing substituents (4-R=-SO(2)Ar, DeltaE1/2=+0.92 V) results in NHC ligands with virtually the same electron-donating capacity as a trialkylphosphine in [IrCl(cod)(PCy3)] (DeltaE1/2 =+0.95 V), while [IrCl(cod)(NHC)] complexes with 4-R=NEt2 (DeltaE1/2= +0.59 V) show drastically more cathodic redox potentials and significantly enhanced donating properties.

BackgroundSauropod dinosaurs were the largest animals ever to walk on land, and, as a result, the evolution of their remarkable adaptations has been of great interest. The braincase is of particular interest because it houses the brain and inner ear. However, only a few studies of these structures in sauropods are available to date. Because of the phylogenetic position of Spinophorosaurus nigerensis as a basal eusauropod, the braincase has the potential to provide key evidence on the evolutionary transition relative to other dinosaurs.Methodology/Principal FindingsThe only known braincase of Spinophorosaurus (‘Argiles de l'Irhazer’, Irhazer Group; Agadez region, Niger) differs significantly from those of the Jurassic sauropods examined, except potentially for Atlasaurus imelakei (Tilougguit Formation, Morocco). The basisphenoids of Spinophorosaurus and Atlasaurus bear basipterygoid processes that are comparable in being directed strongly caudally. The Spinophorosaurus specimen was CT scanned, and 3D renderings of the cranial endocast and inner-ear system were generated. The endocast resembles that of most other sauropods in having well-marked pontine and cerebral flexures, a large and oblong pituitary fossa, and in having the brain structure obscured by the former existence of relatively thick meninges and dural venous sinuses. The labyrinth is characterized by long and proportionally slender semicircular canals. This condition recalls, in particular, that of the basal non-sauropod sauropodomorph Massospondylus and the basal titanosauriform Giraffatitan.Conclusions/Significance Spinophorosaurus has a moderately derived paleoneuroanatomical pattern. In contrast to what might be expected early within a lineage leading to plant-eating graviportal quadrupeds, Spinophorosaurus and other (but not all) sauropodomorphs show no reduction of the vestibular apparatus of the inner ear. This character-state is possibly a primitive retention in Spinophorosaurus, but due the scarcity of data it remains unclear whether it is also the case in the various later sauropods in which it is present or whether it has developed homoplastically in these taxa. Any interpretations remain tentative pending the more comprehensive quantitative analysis underway, but the size and morphology of the labyrinth of sauropodomorphs may be related to neck length and mobility, among other factors.

The Late Jurassic Tendaguru Formation of Tanzania, southeastern Africa, records a rich sauropod fauna, including the diplodocoids Dicraeosaurus and Tornieria, and the brachiosaurid titanosauriform Giraffatitan. However, the taxonomic affinities of other sympatric sauropod taxa are poorly understood. Here, we critically reassess and redescribe these problematic taxa, and present the largest phylogenetic analysis for sauropods (117 taxa scored for 542 characters) to explore their placement within Eusauropoda. Janenschia robusta has played a prominent role in discussions of titanosaur origins, with various authors referring at least some remains to Titanosauria, a clade otherwise known only from the Cretaceous. Re-description of the holotype of Janenschia, and all referable remains, supports its validity and placement as a non-neosauropod eusauropod. It forms a clade with Haestasaurus, from the earliest Cretaceous of the UK, and the Middle/Late Jurassic Chinese sauropod Bellusaurus. Phylogenetic analysis and CT scans of the internal pneumatic tissue structure of Australodocus bohetii tentatively support a non-titanosaurian somphospondylan identification, making it the only known pre-Cretaceous representative of that clade. New information on the internal pneumatic tissue structure of the dorsal vertebrae of the enigmatic Tendaguria tanzaniensis, coupled with a full re-description, results in its novel placement as a turiasaur. Tendaguria is the sister taxon of Moabosaurus, from the Early Cretaceous of North America, and is the first turiasaur recognised from Gondwana. A previously referred caudal sequence cannot be assigned to Janenschia and displays several features that indicate a close relationship with Middle-Late Jurassic East Asian mamenchisaurids. It can be diagnosed by six autapomorphies, and we erect the new taxon Wamweracaudia keranjei gen. et sp. nov. The presence of a mamenchisaurid in the Late Jurassic of southern Gondwana indicates an earlier and more widespread diversification of this clade than previously realised, prior to the geographic isolation of East Asia. Our revised phylogenetic dataset sheds light on the evolutionary history of Eusauropoda, including supporting a basal diplodocoid placement for Haplocanthosaurus, and elucidating the interrelationships of rebbachisaurids. The Tendaguru Formation shares representatives of nearly all sauropod lineages with Middle Jurassic-earliest Cretaceous global faunas, but displays a greater range of diversity than any of those faunas considered individually. Biogeographic analysis indicates that the Tendaguru sauropod fauna was assembled as a result of three main phenomena during the late Early and/or Middle Jurassic: (1) invasions from Euramerica (brachiosaurids, turiasaurs); (2) endemism in west Gondwana (dicraeosaurids, diplodocids); and (3) regional extinctions that restricted the ranges of once widespread groups (mamenchisaurids, the Janenschia lineage). Multiple dispersals across the Central Gondwanan Desert are required to explain the distributions ...

The cross-sectional area of a nutrient foramen of a long bone is related to blood flow requirements of the internal bone cells that are essential for dynamic bone remodelling. Foramen area increases with body size in parallel among living mammals and non-varanid reptiles, but is significantly larger in mammals. An index of blood flow rate through the foramina is about 10 times higher in mammals than in reptiles, and even higher if differences in blood pressure are considered. The scaling of foramen size correlates well with maximum whole-body metabolic rate during exercise in mammals and reptiles, but less well with resting metabolic rate. This relates to the role of blood flow associated with bone remodelling during and following activity. Mammals and varanid lizards have much higher aerobic metabolic rates and exercise-induced bone remodelling than non-varanid reptiles. Foramen areas of 10 species of dinosaur from five taxonomic groups are generally larger than from mammals, indicating a routinely highly active and aerobic lifestyle. The simple measurement holds possibilities offers the possibility of assessing other groups of extinct and living vertebrates in relation to body size, behaviour and habitat.Keywords: metabolic rate; blood flow; bone remodelling; nutrient foramen; allometry INTRODUCTIONThe size of blood vessels is dynamically variable, responding to the blood flow requirements through them. Vessels throughout the body react specifically to greater blood pressures by thickening and strengthening the walls, and to greater shear stress (related to the velocity of the blood) by increasing circumference [1,2]. Organs that have higher metabolic rates require higher flow rates and therefore have larger blood vessels that service them. To test the hypothesis that differences in blood perfusion rates reflect differences in metabolic capacity between species, this study examines the correlations between femoral nutrient foramen size, bone volume, body mass and resting and maximum metabolic rates in living mammals and reptiles. As bones are the only tissues remaining from non-avian dinosaurs, the relationships between nutrient foramina size and metabolic capacity developed for mammals and reptiles can indicate the levels of activity and metabolic status of dinosaurs.Long bones of all amniotes, comprising the reptiles, mammals and birds, receive blood from three sources: (i) nutrient vessels, (ii) metaphyseal and epiphyseal vessels that combine after the cartilaginous growth plate is closed and (iii) periosteal vessels [3]. The nutrient system contributes around 50 -70% of the blood supply