The evolution of mammal-like crocodyliforms in the Cretaceous Period of Gondwana.

Fossil crocodyliforms discovered in recent years have revealed a level of morphological and ecological diversity not exhibited by extant members of the group. This diversity is particularly notable among taxa of the Cretaceous Period (144-65 million years ago) recovered from former Gondwanan landmasses. Here we report the discovery of a new species of Cretaceous notosuchian crocodyliform from the Rukwa Rift Basin of southwestern Tanzania. This small-bodied form deviates significantly from more typical crocodyliform craniodental morphologies, having a short, broad skull, robust lower jaw, and a dentition with relatively few teeth that nonetheless show marked heterodonty. The presence of morphologically complex, complementary upper and lower molariform teeth suggests a degree of crown-crown contact during jaw adduction that is unmatched among known crocodyliforms, paralleling the level of occlusal complexity seen in mammals and their extinct relatives. The presence of another small-bodied mammal-like crocodyliform in the Cretaceous of Gondwana indicates that notosuchians probably filled niches and inhabited ecomorphospace that were otherwise occupied by mammals on northern continents.

Respirable dust and quartz exposure from three South African farms with sandy, sandy loam, and clay soils.

OBJECTIVES: To quantify personal time-weighted average respirable dust and quartz exposure on a sandy, a sandy loam, and a clay soil farm in the Free State and North West provinces of South Africa and to ascertain whether soil type is a determinant of exposure to respirable quartz. METHODS: Three farms, located in the Free State and North West provinces of South Africa, had their soil type confirmed as sandy, sandy loam, and clay; and, from these, a total of 298 respirable dust and respirable quartz measurements were collected between July 2006-November 2009 during periods of major farming operations. Values below the limit of detection (LOD) (22 µg · m(-3)) were estimated using multiple 'imputation'. Non-parametric tests were used to compare quartz exposure from the three different soil types. RESULTS: Exposure to respirable quartz occurred on all three farms with the highest individual concentration measured on the sandy soil farm (626 µg · m(-3)). Fifty-seven, 59, and 81% of the measurements on the sandy soil, sandy loam soil, and clay soil farm, respectively, exceeded the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) of 25 µg · m(-3). Twelve and 13% of respirable quartz concentrations exceeded 100 µg · m(-3) on the sandy soil and sandy loam soil farms, respectively, but none exceeded this level on the clay soil farm. The proportions of measurements >100 µg · m(-3) were not significantly different between the sandy and sandy loam soil farms ('prop.test'; P = 0.65), but both were significantly larger than for the clay soil farm ('prop.test'; P = 0.0001). The percentage of quartz in respirable dust was determined for all three farms using measurements > the limit of detection. Percentages ranged from 0.5 to 94.4% with no significant difference in the median quartz percentages across the three farms (Kruskal-Wallis test; P = 0.91). CONCLUSION: This study demonstrates that there is significant potential for over-exposure to respirable quartz in farming and even clay soil farming may pose a risk. Soil type may determine whether exposure is >100 µg · m(3), but the job type and the manner in which the task is performed (e.g. mechanical or manual) may be important determinants of exposure. Identifying quartz exposure determinants (e.g. type of job) and modifiers will be of value to focus implementation of controls of particular importance in developing countries.

A New Centrosaurine Ceratopsid, Machairoceratops cronusi gen et sp. nov., from the Upper Sand Member of the Wahweap Formation (Middle Campanian), Southern Utah.

The Upper Cretaceous (middle-late Campanian) Wahweap Formation of southern Utah contains the oldest diagnostic evidence of ceratopsids (to date, all centrosaurines) in North America, with a number of specimens recovered from throughout a unit that spans between 81 and 77 Ma. Only a single specimen has been formally named, Diabloceratops eatoni, from the lower middle member of the formation. Machairoceratops cronusi gen. et sp. nov., a new centrosaurine ceratopsid from the upper member of the Wahweap Formation, is here described based on cranial material representing a single individual recovered from a calcareous mudstone. The specimen consists of two curved and elongate orbital horncores, a left jugal, a nearly complete, slightly deformed braincase, the left squamosal, and a mostly complete parietal ornamented by posteriorly projected, anterodorsally curved, elongate spikes on either side of a midline embayment. The fan-shaped, stepped-squamosal is diagnostic of Centrosaurinae, however, this element differs from the rectangular squamosal in Diabloceratops. Machairoceratops also differs in the possession of two anterodorsally (rather than laterally) curved epiparietal ornamentations on either side of a midline embayment that are distinguished by a posteromedially-oriented sulcus along the entire length of the epiparietal. Additionally, the parietosquamosal frill is lacking any other epiossifications along its periphery. Machairoceratops shares a triangular (rather than round) frill and spike-like epiparietal loci (p1) ornamentation with the stratigraphically lower Diabloceratops. Both parsimony and Bayesian phylogenetic analyses place Machairoceratops as an early-branching centrosaurine. However, the parsimony-based analysis provides little resolution for the position of the new taxon, placing it in an unresolved polytomy with Diabloceratops. The resultant Bayesian topology yielded better resolution, aligning Machairoceratops as the definitive sister taxon to a clade formed by Diabloceratops and Albertaceratops. Considered together, both phylogenetic methods unequivocally place Machairoceratops as an early-branching centrosaurine, and given the biostratigraphic position of Machairoceratops, these details increase the known ceratopsid diversity from both the Wahweap Formation and the southern portion of Laramidia. Finally, the unique morphology of the parietal ornamentation highlights the evolutionary disparity of frill ornamentation near the base of Centrosaurinae.