Elastic symmetries of defective crystals

I construct discrete and continuous crystal structures that are compatible with a given choice of dislocation density tensor, and (following Mal’cev) provide a canonical form for these discrete structures. The symmetries of the discrete structures extend uniquely to symmetries of corresponding continuous structures—I calculate these symmetries explicitly for a particular choice of dislocation density tensor and deduce corresponding constraints on energy functions which model defective crystals

A new large-bodied oviraptorosaurian theropod dinosaur from the Latest Cretaceous of Western North America

The oviraptorosaurian theropod dinosaur clade Caenagnathidae has long been enigmatic due to the incomplete nature of nearly all described fossils. Here we describe Anzu wyliei gen. et sp. nov., a new taxon of large-bodied caenagnathid based primarily on three well-preserved partial skeletons. The specimens were recovered from the uppermost Cretaceous (upper Maastrichtian) Hell Creek Formation of North and South Dakota, and are therefore among the stratigraphically youngest known oviraptorosaurian remains. Collectively, the fossils include elements from most regions of the skeleton, providing a wealth of information on the osteology and evolutionary relationships of Caenagnathidae. Phylogenetic analysis reaffirms caenagnathid monophyly, and indicates that Anzu is most closely related to Caenagnathus collinsi, a taxon that is definitively known only from a mandible from the Campanian Dinosaur Park Formation of Alberta. The problematic oviraptorosaurs Microvenator and Gigantoraptor are recovered as basal caenagnathids, as has previously been suggested. Anzu and other caenagnathids may have favored well-watered floodplain settings over channel margins, and were probably ecological generalists that fed upon vegetation, small animals, and perhaps eggs

A new genus and species for the largest specimen of Archaeopteryx

The Solnhofen (Sixth) specimen of Archaeopteryx is assigned to Wellnhoferia grandis gen. et sp. n. on the basis of qualitative, size-independent autapomorphies. Wellnhoferia differs from Archaeopteryx in a short tail with the estimated number of 16-17 caudals; a nearly symmetric pattern of pedal rays II-IV with metatarsals II and IV of equal length and digit IV substantially shorter than in Archaeopteryx; and the number of four (instead of five) phalanges of pedal digit IV, which most probably results from a phylogenetic reduction rather than individual variation. A combination of large size and details of the pelvic limb suggests a locomotor specialization different from that of Archaeopteryx.Solnhofeński, czyli szósty okaz praptaków przeniesiony zostaje z Archaeopteryx lithographica von Meyer, 1861 do Wellnhoferia grandis gen. et sp. n. na podstawie autapomorfii niezależnych od wielkości ciała, w tym cech jakościowych, merystycznych i proporcji. Okaz ten różni się od okazów Archaeopteryx krótszym ogonem o szacunkowej liczbie kręgów 16-17, bardziej symetryczną budową stopy z kośćmi sródstopia II i IV jednakowej długości i palcem IV zbliżonym długością do palca II, a więc znacznie krótszym niż u Archaeopteryx, i składającym się z 4 zamiast 5 paliczków. Taka budowa stopy przy stosunkowo dużych rozmiarach ciała sugeruje również nieco inną niż u Archaeopteryx, prawdopodobnie bardziej kursorialną, specjalizację lokomototyczną

More evidence for plesiomorphy of the quadrate in the Eocene anseriform avian genus Presbyornis

Evidence from the quadrate morphology in the American specimens of Presbyornis proved inconsistent with the hypothesis of close relationships of this anseriform genus to modern ducks and geese, but some character states remained uncertain. Here I describe in detail two fairly well preserved Presbyornis quadrates from Central Asia, which provide new evidence for the plesiomorphic, galliform-like morphology of this bone among the anseriforms. Most important, and contrary to a recent report, there is no caudomedial foramen that is present in the extant anseriforms. The only pneumatic foramen is in the basiorbital position, which is plesiomorphic for the galloanserines. At least six other plesiomorphic characters of the quadrate consistently suggest that the Presbyornithidae are stem-group anseriforms