Philip J. Currie

Two feathered dinosaurs from northeastern China

Current controversy over the origin and early evolution of birds centres on whether or not they are derived from coelurosaurian theropod dinosaurs. Here we describe two theropods from the Upper Jurassic/Lower Cretaceous Chaomidianzi Formation of Liaoning province, China. Although both theropods have feathers, it is likely that neither was able to fly. Phylogenetic analysis indicates that they are both more primitive than the earliest known avialan (bird), Archaeopteryx. These new fossils represent stages in the evolution of birds from feathered, ground-living, bipedal dinosaurs.

Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs

How evolutionary changes in body size are brought about by variance in developmental timing and/or growth rates (also known as heterochrony) is a topic of considerable interest in evolutionary biology. In particular, extreme size change leading to gigantism occurred within the dinosaurs on multiple occasions. Whether this change was brought about by accelerated growth, delayed maturity or a combination of both processes is unknown. A better understanding of relationships between non-avian dinosaur groups and the newfound capacity to reconstruct their growth curves make it possible to address these questions quantitatively. Here we study growth patterns within the Tyrannosauridae, the best known group of large carnivorous dinosaurs, and determine the developmental means by which Tyrannosaurus rex, weighing 5,000 kg and more, grew to be one of the most enormous terrestrial carnivorous animals ever. T. rex had a maximal growth rate of 2.1 kg d-1, reached skeletal maturity in two decades and lived for up to 28 years. T. rexs great stature was primarily attained by accelerating growth rates beyond that of its closest relatives.

New information on the anatomy and relationships of Dromaeosaurus albertensis (Dinosauria: Theropoda)

ABSTRACT Dromaeosaurus albertensis was one of the first small theropods described that was based on reasonably good cranial material. It was realized from the beginning that this animal was significantly different from other Cretaceous theropods, and the Dromaeosauridae was created for its inclusion. In the intervening years, a number of genera were assigned to this family, which came to assume an important position in discussions on theropod relationships and evolution, and the origin of birds. It is now known that many of the dromaeosaurids are different enough from Dromaeosaurus to be included in a distinct subfamily known as the Velociraptorinae. In spite of intensive collecting activity, the holotype of Dromaeosaurus albertensis is still the most complete specimen, and it is apparent that this genus is even rarer than other small theropods. Repreparation and restudy of the holotype has produced new anatomical information useful for evaluating the relationships of dromaeosaurids. Contrary to previous ...

Bird-like characteristics of the jaws and teeth of troodontid theropods (Dinosauria, Saurischia)

ABSTRACT The discovery of a new dentary of “Stenonychosaurus inequalis” with six germ teeth prompted a critical examination of all jaws and teeth attributed to Troodon, Stenonychosaurus, and Pectinodon. It is concluded that Troodon is the senior synonym of these genera, and that the name Troodontidae has priority over Saurornithoididae. Troodontid dentaries are unique amongst the Theropoda in that they lack interdental plates. Previous reports that Dromaeosaurus, Deinonychus, and Saurornitholestes do not have interdental plates are erroneous. Premaxillary, maxillary, anterior dentary and dentary teeth can be distinguished from each other. Each troodontid tooth has a constriction between the crown and root that is more comparable with birds and crocodiles than with other theropods.

The Taphonomy of a Centrosaurus (Ornithischia: Certopsidae) Bone Bed from the Dinosaur Park Formation (Upper Campanian), Alberta, Canada, with Comments on Cranial Ontogeny

Abstract Bone bed 43 is one of at least eight paucispecific Centrosaurus bone beds located in the Dinosaur Park Formation (Upper Campanian) in Dinosaur Provincial Park, Alberta, Canada. It long has been used as a case example for evidence of herding and social behavior in dinosaurs, but a detailed analysis of the site has not been presented until this study. The bone bed is dominated by the disarticulated, mostly fragmentary and slightly abraded remains of Centrosaurus apertus, with minor occurrences of other taxa, notably teeth from the large tyrannosaurid Albertosaurus libratus. Fossils occur in a stacked to amalgamated succession of lag deposits, deposited and reworked at the erosional base of a paleochannel. The most parsomonious scenerio suggests that Centrosaurus material represents part of a large aggregation of animals (possibly numbering in the thousands) that died by drowning on the alluvial plain. Disarticulation occurred at a point upriver from the bone-bed site. Scavenging by theropods, primarily Albertosaurus, at or near the original site of death is suggested by the high number of shed theropod teeth. A subsequent event prior to fossilisation moved the material to its present location removing many juvenile-sized and hydrodynamically light elements from the original death assemblage. Evidence for distinct size classes amongst the preserved elements is not supported by the data, but the size range of elements preserved are representative of living individuals that would have ranged from small juveniles to mature adults. The large data base of specimens from bone bed 43 allows for the illustration of the ontogenetic changes that occurred in the diagnostic cranial elements of Centrosaurus.

Cranial anatomy of tyrannosaurid dinosaurs from the Late Cretaceous of Alberta, Canada

Beautifully preserved, nearly complete theropod skeletons from Alberta (Canada) allow re−evaluation of the taxonomic status of North American tyrannosaurids. It is concluded that the most parsimonious interpretation of relationships leads to the separation of the two species of Albertosaurus (sensu Russell 1970) into Gorgosaurus libratus from the Campanian Dinosaur Park Formation and Albertosaurus sarcophagus from the upper Campanian/lower Maastrichtian Horseshoe Canyon Formation. Albertosaurus and Gorgosaurus are closely related, but can be distinguished from each other by more characters than are known to justify generic distinction within another tyrannosaurid clade that includes Daspletosaurus, Tarbosaurus and Tyrannosaurus. Daspletosaurus is known from multiple species that cover extensive geographic, eco− logical and temporal ranges, and it is sensible to maintain its generic distinction from Tyrannosaurus. All tyrannosaurid species have consistent ontogenetic trends. However, one needs to be cautious in assessing ontogenetic stage because many characters are size−dependent rather than age−dependent. There are relatively few osteological differences that can distinguish tyrannosaurid species at any age. For example, Nanotyrannus lancensis is probably a distinct species from Tyrannosaurus rex because there is no evidence of ontogenetic reduction of tooth counts in any other tyrannosaurid spe− cies. Some characters that are good for separating mature tyrannosaurids, such as differences in the sizes and shapes of maxillary fenestrae, are not useful for identifying the species of juveniles.

SMALL THEROPOD AND BIRD TEETH FROM THE LATE CRETACEOUS (LATE CAMPANIAN) JUDITH RIVER GROUP, ALBERTA

Abstract A collection of over 1,700 small theropod teeth from the Judith River Group (Campanian; ∼79.5–74 Ma) allows our understanding of the diversity and variation of small theropods in this assemblage to be refined. In addition to the previously recognized taxa, a series of morphologically distinct groups are recognized that may represent distinct taxa in some cases. Teeth with the Paronychodon-like features of a flat surface with longitudinal ridges on one side are resolved into a few discrete morphotypes. Two of these are included in Paronychodon lacustris and two additional morphotypes are hypothesized to represent distinct taxa, here referred to as ?Dromaeosaurus morphotype A and Genus and species indet. A. The teeth of Paronychodon lacustris and ?Dromaeosaurus morphotype A share a distinctive wear pattern that suggests tooth functioning involved contact between the flat surfaces of opposing teeth. Two species of Richardoestesia, R. gilmorei and R. isosceles, are present in the assemblage. Additionally, bird teeth are identified in the assemblage and are described in this review. Bivariate plots were used to document the variation in the theropod teeth, especially in the features that distinguish between Richardoestesia gilmorei, R. isosceles, Saurornitholestes, and Dromaeosaurus. Considerable overlap is present in all plots, so although the teeth are morphologically distinct, they are not easily distinguished by quantitative means.

A Diverse Dinosaur-Bird Footprint Assemblage from the Lance Formation, Upper Cretaceous, Eastern Wyoming: Implications for Ichnotaxonomy

A diverse assemblage of dinosaur and bird tracks from Niobrara County, Wyoming, represents the first vertebrate ichnofauna reported from the bone-rich Lance Formation (Maastrichtian, Upper Cretaceous). The ichnofauna includes a hadrosaur track with skin impressions; three theropod track types, including the tetradactyl track Saurexallopus zerbsti (ichnosp. nov.); a tridactyl dinosaur footprint with a fusiform digit III; possible Tyrannosaurus tracks; four distinctive avian ichnites; and invertebrate traces. The footprints are generally well-preserved and so offer a unique insight into the ecology of a small river valley during the Maastrichtian. Saurexallopus zerbsti ichnosp. nov. from the Lance is similar to Saurexallopus lovei recently reported from the Maastrichtian, Harebell Formation, of northwestern Wyoming, but is represented by much better material, facilitating amendment of the ichnogenus. Skeletal equivalents for Saurexallopus are not currently known. Similarly, the tridactyl track with fusiform...

Cretaceous Extinctions: Multiple Causes

![Figure][1] Deccan plateau basalts. Lava from Deccan volcanism formed distinct layering. CREDIT: GSFC/NASA In the Review “The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene boundary” (P. Schulte et al. , 5 March, p. [1214][2]), the terminal Cretaceous

Hadrosaur trackways from the Lower Cretaceous of Canada

The most common ichnogenus in the Peace River Canyon is Amblydactylus, a large bipedal herbivore. The morphology of the hand a nd footprints suggest that the tracks and trackways were made by hadrosaurs, and the ichnites might represent the earliest record of these dinosaurs. Amblydactylus tracks were made in a wide variety of depositional environments, including the mud beneath several metres of water. Juveniles were gregarious and stayed together after hatching until they were large enough to join herds of more mature animals. Hadrosaur herds appear to have walked side by side, seldom crossing paths, although there was little structure to the herds when they were in the water and/or feeding. Calculation of the walking speeds indicate that the herbivores were generally slower than the carnivores.