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Farke A.A.,Raymond M. Alf Museum of Paleontology | Sertich J.J.W.,Denver Museum of Nature and Science
PLoS ONE | Year: 2013

Geophysical evidence strongly supports the complete isolation of India and Madagascar (Indo-Madagascar) by ~100 million years ago, though sparse terrestrial fossil records from these regions prior to ~70 million years ago have limited insights into their biogeographic history during the Cretaceous. A new theropod dinosaur, Dahalokely tokana, from Turonian-aged (~90 million years old) strata of northernmost Madagascar is represented by a partial axial column. Autapomorphies include a prominently convex prezygoepipophyseal lamina on cervical vertebrae and a divided infraprezygapophyseal fossa through the mid-dorsal region, among others. Phylogenetic analysis definitively recovers the species as an abelisauroid theropod and weakly as a noasaurid. Dahalokely is the only known dinosaur from the interval during which Indo-Madagascar likely existed as a distinct landmass, but more complete material is needed to evaluate whether or not it is more closely related to later abelisauroids of Indo-Madagascar or those known elsewhere in Gondwana. © 2013 Farke, Sertich. Source

Hagadorn J.W.,Denver Museum of Nature and Science | Mcdowell C.,111 Lee Circle
Sedimentology | Year: 2012

Interpreting the physical dynamics of ancient environments requires an understanding of how current-generated sedimentary structures, such as ripples and dunes, are created. Traditional interpretations of these structures are based on experimental flume studies of unconsolidated quartz sand, in which stepwise increases in flow velocity yield a suite of sedimentary structures analogous to those found in the rock record. Yet cyanobacteria, which were excluded from these studies, are pervasive in wet sandy environments and secrete sufficient extracellular polysaccharides to inhibit grain movement and markedly change the conditions under which sedimentary structures form. Here, the results of flume experiments using cyanobacteria-inoculated quartz sand are reported which demonstrate that microbes strongly influence the behaviour of unconsolidated sand. In medium sand, thin (ca 0·1 to 0·5mm thick) microbial communities growing at the sediment-water interface can nearly double the flow velocity required to produce the traditional sequence of ripple→dune→plane-bed lamination bedforms. In some cases, these thin film-like microbial communities can inhibit the growth of ripples or dunes entirely, and instead bed shear stresses result in flip-over and rip-up structures. Thicker (ca≥1mm thick) microbial mats mediate terracing of erosional edges; they also, foster transport of multi-grain aggregates and yield a bedform progression consisting of flip-overs→roll-ups→rip-ups of bound sand. © 2011 The Authors. Journal compilation © 2011 International Association of Sedimentologists. Source

Krell F.-T.,Denver Museum of Nature and Science
European Science Editing | Year: 2012

The Journal Impact Factor is the most commonly applied metric for evaluation of scientific output. It is a journalfocused indicator that shows the attention a journal attracts. It does not necessarily indicate quality, but high impact factors indicate a probability of high quality. As an arithmetic mean of data originating from all authors of a journal with a high variance, it is inapplicable to evaluate individual scientists. For quantifying the performance of authors, author-focused citation metrics are to be used, such as the h index, but self-citations should be excluded ("honest h index" h). All citation metrics suffer from the incompleteness of the databases they source their data from. This incompleteness is unequally distributed between disciplines, countries and language-groups. The Journal Impact Factor has its limitations, but if those limitations are taken into consideration, it is still an appropriate indicator for journal performance. Source

Sampson S.D.,Denver Museum of Nature and Science
Proceedings. Biological sciences / The Royal Society | Year: 2013

The fossil record of centrosaurine ceratopsids is largely restricted to the northern region of western North America (Alberta, Montana and Alaska). Exceptions consist of single taxa from Utah (Diabloceratops) and China (Sinoceratops), plus otherwise fragmentary remains from the southern Western Interior of North America. Here, we describe a remarkable new taxon, Nasutoceratops titusi n. gen. et sp., from the late Campanian Kaiparowits Formation of Utah, represented by multiple specimens, including a nearly complete skull and partial postcranial skeleton. Autapomorphies include an enlarged narial region, pneumatic nasal ornamentation, abbreviated snout and elongate, rostrolaterally directed supraorbital horncores. The subrectangular parietosquamosal frill is relatively unadorned and broadest in the mid-region. A phylogenetic analysis indicates that Nasutoceratops is the sister taxon to Avaceratops, and that a previously unknown subclade of centrosaurines branched off early in the group's history and persisted for several million years during the late Campanian. As the first well-represented southern centrosaurine comparable in age to the bulk of northern forms, Nasutoceratops provides strong support for the provincialism hypothesis, which posits that Laramidia-the western landmass formed by inundation of the central region of North America by the Western Interior Seaway-hosted at least two coeval dinosaur communities for over a million years of late Campanian time. Source

Miller I.M.,Denver Museum of Nature and Science | Hickey L.J.,Yale University
Bulletin of the Peabody Museum of Natural History | Year: 2010

The Winthrop Flora is of middle to late Albian age (Early Cretaceous) and occurs in the Methow basin of north-central Washington State, USA. With an estimated diversity of more than 150 species, the Winthrop is the most diverse flora yet described from the Early Cretaceous of North America. This paper deals with the 38 species of gymnosperms or Pinophytina of the Winthrop Formation, consisting of three species of Pteridospermopsida, three of Cycadopsida, three of Ginkgoopsida, nine of Bennittopsida, 15 of conifers or Pinopsida, and five species whose assignment is uncertain below the level of the gymnosperms. We describe four new genera and 21 new species of Pinophytina. Overall, the gymnosperm component of the flora is concordant with that of other late Early Cretaceous floras of the Northern Hemisphere. However, several of its species are similar to those found in Jurassic sediments from Mexico and Central America and some of the cycadophytes and conifers have what we interpret as xeromorphic foliage. © 2010 Peabody Museum of Natural History. Source

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