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de Souza Carvalho, I., de Vasconcellos, F.M., and Simionato Tavares, S.A.
2007. Montealtosuchus arrudacamposi, a new peirosaurid crocodile
(Mesoeucrocodylia) from the Late Cretaceous Adamantina Formation of Brazil.
ABSTRACT: We describe a new species of Peirosauridae (Crocodyliformes, Mesoeucrocodylia), Montealtosuchus arrudacamposi gen. nov. et sp. nov., from the Late Cretaceous (Turonian-Santonian) strata of the Bauru Basin, Brazil.
Montealtosuchus was found at the outskirts of Monte Alto County in reddish sandstones of the Adamantina Formation. This specimen is exquisitely preserved with skull, mandible, postcranial and exoskeletal elements in articulation that provides critical information of the anatomy of this group. The occurrence of Peirosauridae in the Adamantina Formation
(Turonian-Santonian) widens the chronostratigraphic range of this Mesoeucrocodylia taxon in Brazil. Recent analysis suggests that the Peirosauridae is restricted to the Late Cretaceous deposits of South America.
Butler, R.J., Upchurch, P., and Norman, D.B. 2007. The phylogeny of the ornithischian dinosaurs. Journal of Systematic Palaeontology
ABSTRACT: Ornithischia is a familiar and diverse clade of dinosaurs whose global phylogeny has remained largely unaltered since early cladistic analyses in the mid 1980s. Current understanding of ornithischian evolution is hampered by a paucity of explicitly numerical phylogenetic analyses that consider the entire clade. As a result, it is difficult to assess the robustness of current phylogenetic hypotheses for Ornithischia and the effect that the addition of new taxa or characters is likely to have on the overall topology of the clade.
The new phylogenetic analysis presented here incorporates a range of new basal taxa and characters in an attempt to rigorously test global ornithischian phylogeny. Parsimony analysis is carried out with 46 taxa and
221 characters. Although the strict component consensus tree shows poor resolution in a number of areas, application of reduced consensus methods provides a well-resolved picture of ornithischian interrelationships.
Surprisingly, Heterodontosauridae is placed as the most basal group of all well-known ornithischians, phylogenetically distant from a stem-defined Ornithopoda, creating a topology that is more congruent with the known ornithischian stratigraphical record. There is no evidence for a monophyletic 'Fabrosauridae', and Lesothosaurus (the best-known 'fabrosaur') occupies an unusual position as the most basal member of Thyreophora. Other relationships within Thyreophora remain largely stable. The primitive thyreophoran Scelidosaurus is the sister taxon of Eurypoda (stegosaurs and ankylosaurs), rather than a basal ankylosaur as implied by some previous studies.
The taxonomic content of Ornithopoda differs significantly from previous analyses and basal relationships within the clade are weakly supported, requiring further investigation. 'Hypsilophodontidae' is paraphyletic, with some taxa (Agilisaurus, Hexinlusaurus, Othnielia) placed outside of Ornithopoda as non-cerapodans. Ceratopsia and Pachycephalosauria are monophyletic and are united as Marginocephalia; however, the stability of these clades is reduced by a number of poorly preserved basal taxa.
This analysis reaffirms much of the currently accepted ornithischian topology. Nevertheless, instability in the position and content of several clades (notably Heterodontosauridae and Ornithopoda) indicates that considerable future work on ornithischian phylogeny is required and causes problems for several current phylogenetic definitions.
Snively, E., and Russell, A.P. 2007. Craniocervical feeding dynamics of Tyrannosaurus rex. Paleobiology
33(4):610-638. doi: 10.1666/06059.1.
ABSTRACT: Tyrannosaurus rex and other tyrannosaurid theropods exerted high bite forces, and large muscle attachments suggest that the tyrannosaurid neck was a concomitantly powerful component of the feeding apparatus. We examine accelerative and work-generating capacity (WGC) of neck muscles in adult Tyrannosaurus rex, using a 3-D vector-based method that incorporates aspects of muscle force generation, reconstruction of muscle morphology and moment arms, and rotational inertias of the head and neck. Under conservative assumptions, radial accelerations of the head by large superficial muscles (M. transversospinalis capitis, M. complexus, and M.
longissimus capitis superficialis) enabled rapid gaze shifts and imparted high tangential velocities to food sufficient for inertial feeding. High WGC by these and deeper muscles under eccentric contraction indicate high efficacy for tearing flesh, especially with the head and neck in an extended posture. Sensitivity analyses suggest that assigned density of the antorbital region has substantial effects on calculated rotational inertia, and hence on the accuracy of results. However, even with high latitude for estimation errors, the results indicate that adult T. rex could strike rapidly at prey and engage in complexly modulated inertial feeding, as seen in extant archosaurs.
posted at 21:24:23 on 10/30/07
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Category: New Paper