David A. Eberth

A Jurassic ceratosaur from China helps clarify avian digital homologies

Theropods have traditionally been assumed to have lost manual digits from the lateral side inward, which differs from the bilateral reduction pattern seen in other tetrapod groups. This unusual reduction pattern is clearly present in basal theropods, and has also been inferred in non-avian tetanurans based on identification of their three digits as the medial ones of the hand (I-II-III). This contradicts the many developmental studies indicating II-III-IV identities for the three manual digits of the only extant tetanurans, the birds. Here we report a new basal ceratosaur from the Oxfordian stage of the Jurassic period of China (156–161 million years ago), representing the first known Asian ceratosaur and the only known beaked, herbivorous Jurassic theropod. Most significantly, this taxon possesses a strongly reduced manual digit I, documenting a complex pattern of digital reduction within the Theropoda. Comparisons among theropod hands show that the three manual digits of basal tetanurans are similar in many metacarpal features to digits II-III-IV, but in phalangeal features to digits I-II-III, of more basal theropods. Given II-III-IV identities in avians, the simplest interpretation is that these identities were shared by all tetanurans. The transition to tetanurans involved complex changes in the hand including a shift in digit identities, with ceratosaurs displaying an intermediate condition.

A basal tyrannosauroid dinosaur from the Late Jurassic of China.

The tyrannosauroid fossil record is mainly restricted to Cretaceous sediments of Laurasia, although some very fragmentary Jurassic specimens have been referred to this group. Here we report a new basal tyrannosauroid, Guanlong wucaii gen. et sp. nov., from the lower Upper Jurassic of the Junggar Basin, northwestern China. G. wucaii is the oldest known tyrannosauroid and shows several unexpectedly primitive pelvic features. Nevertheless, the limbs of G. wucaii share several features with derived coelurosaurs, and it possesses features shared by other coelurosaurian clades. This unusual combination of character states provides an insight into the poorly known early radiation of the Coelurosauria. Notably, the presumed predatory Guanlong has a large, fragile and highly pneumatic cranial crest that is among the most elaborate known in any non-avian dinosaur and could be comparable to some classical exaggerated ornamental traits among vertebrates.

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.

Stratigraphy, sedimentology and evolution of a vertebrate-bearing, braided to anastomosed fluvial system, Cutler Formation (Permian-Pennsylvanian), north-central New Mexico

Abstract Cutler Formation redbeds, exposed in north-central New Mexico, contain portions of three megasequences, each with different architectural element and lithofacies compositions. Eight architectural elements are recognized including major sandstone sheets and ribbons of braided and anastomosed fluvial origin, respectively. The remaining six elements are of overbank origin and include crevasse channel and splay deposits, and floodplain sand-, silt- and claystones. The megasequence stratigraphy provides a framework in which to assess the evolution of depositional style through approximately 15 million years. Cutler Formation rivers flowed south-southwest from the San Luis-Uncompahgre Uplift from Late Pennsylvanian to Early Permian. During megasequence 1 ‘time’, the climate was semi-arid, major channels were broad and shallow, interfluve areas were frequently inundated by sheet floods and splays, and floodbasin ponds were common. During megasequence 2 ‘tim’, channels became narrower. Laterally extensive floodplains and basins developed between stable channel belts and were sites of mature caliche development. Locally, anastomosed channel reaches developed and associated crevasse channels were a locus for the preservation of macroplant and vertebrate fossils. The climate, though still semi-arid, was more arid than during megasequence 1 ‘time’. Renewed uplift in the highlands during megasequence 3 ‘time’ flooded the region with coarse clastics and reestablished a style of poorly confined shallow, braided flow. Throughout this time, aridity continued to increase. In the San Diego Canyon area, flow was deflected toward the southeast due to minor uplift in the Nacimiento highland.

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

Remarkable Preservation of Undigested Muscle Tissue Within a Late Cretaceous Tyrannosaurid Coprolite from Alberta, Canada

Abstract Exceptionally detailed soft tissues have been identified within the fossilized feces of a large Cretaceous tyrannosaurid. Microscopic cord-like structures in the coprolitic ground mass are visible in thin section and with scanning electron microscopy. The morphology, organization, and context of these structures indicate that they are the fossilized remains of undigested muscle tissue. This unusual discovery indicates specific digestive and taphonomic conditions, including a relatively short gut-residence time, rapid lithification, and minimal diagenetic recrystallization. Rapid burial of the feces probably was facilitated by a flood event on the ancient coastal lowland plain on which the fecal mass was deposited.

Lower Permian Terrestrial Paleoenvironments and Vertebrate Paleoecology of the Tambach Basin (Thuringia, Central Germany): The Upland Holy Grail

Abstract The Bromacker section of the Lower Permian, Tambach Formation, in central Germany, yields an important fossil-vertebrate assemblage that was deposited in an upland setting near the center of a small, internally-drained paleo-graben. The fossil-vertebrate assemblage shares many taxa in common with others that are well-documented from North America, but is atypical in the: (1) unusually large abundance of the terrestrial herbivore Diadectes; (2) complete absence of aquatic and semi-aquatic vertebrates; and (3) rarity of medium-to-large carnivorous synapsids. The graben setting and the low-diversity, terrestrial, fossil-vertebrate assemblage together comprise a unique upland paleoecosystem, heretofore undocumented in the Early Permian. The composition of and relative abundances within the assemblage at Bromacker suggest that experiments with “high-fiber” vertebrate herbivores as the dominant or significant basal component of vertebrate food webs had begun by the Early Permian, but only in settings with few or no aquatic and semi-aquatic vertebrates. The combined stratigraphic section at Bromacker consists of portions of two conformable stratigraphic intervals—the Lower and the Upper beds. Depositional events in both were dominated by seasonal-to-subseasonal cycles of flooding in an ephemeral, alluvial-to-lacustrine setting that was hot year-round with annual precipitation similar to that of a wet-and-dry tropical or wetter climate. Excellently preserved, articulated and disarticulated fossil vertebrates indicate subaerial exposure times of short duration and limited reworking. In the case of articulated specimens, death and burial were probably coeval events, most likely caused by floods.

The paleogeographic and stratigraphic distribution of ceratopsids (Ornithischia) in the upper Judith River Group of Western Canada

Articulated remains and teeth preserved in vertebrate microfossil localities are used as independent lines of evidence to quantify the relative abundances of dinosaurs along a 250-km transect extending from the paleogeographically more inland Dinosaur Provincial Park area (Alberta), through the South Saskatchewan River area, to the more coastal Unity, Saskatchewan locality. A comparison of articulated dinosaur remains along chronostratigraphically equivalent horizons from the Dinosaur Provincial Park and South Saskatchewan areas indicate that ceratopsid dinosaurs are more abundant in the South Saskatchewan River area, whereas the converse is true for ankylosaur and pachycephalosaur dinosaurs. In the case of ceratopsid dinosaurs, the same distributional pattern is reflected in data amassed from vertebrate microfossil assemblages from these areas. In addition, vertebrate microfossil assemblages show that ceratopsids increase in relative abundance moving upsection in both the Dinosaur Park and South Saskatchewan River areas. In these same sections ankylosaurs and pachycephalosaurs decrease in abundance in the Dinosaur Park area, but their abundances show no change up through the section in the South Saskatchewan River area. These paleogeographic and stratigraphic patterns further support the existing hypothesis that ceratopsids were relatively more abundant in coastal areas, rather than inland areas, during the Campanian. They also provide tentative support for the hypothesis that ankylosaurs and pachycephalosaurs were, in general, more prominent members of inland communities.

Feathered Non-Avian Dinosaurs from North America Provide Insight into Wing Origins

Fancy Feathers In the past few decades, an increasing number of dinosaurs have been shown to have possessed feathers. While it seems likely that feathers themselves may have evolved for thermoregulation, the original function of wings has been less clear and remained a matter of debate. Based on examination of three Theropod specimens from the genus Ornothomimus, Zelenitsky et al. (p. 510) conclude that the feathered wing may have evolved not for locomotion or prey capture (the animals were herbivores), but rather as a courtship display. All of the individuals examined had a covering consisting of short filamentous feathers, but the adult specimens, which would have reached sexual maturity, also had long shafted feathers on their forelimbs. Analysis of feathered theropod fossils from North America suggests that feathers may have first evolved for display. Previously described feathered dinosaurs reveal a fascinating record of feather evolution, although substantial phylogenetic gaps remain. Here we report the occurrence of feathers in ornithomimosaurs, a clade of non-maniraptoran theropods for which fossilized feathers were previously unknown. The Ornithomimus specimens, recovered from Upper Cretaceous deposits of Alberta, Canada, provide new insights into dinosaur plumage and the origin of the avian wing. Individuals from different growth stages reveal the presence of a filamentous feather covering throughout life and winglike structures on the forelimbs of adults. The appearance of winglike structures in older animals indicates that they may have evolved in association with reproductive behaviors. These specimens show that primordial wings originated earlier than previously thought, among non-maniraptoran theropods.

VELAFRONS COAHUILENSIS, A NEW LAMBEOSAURINE HADROSAURID (DINOSAURIA: ORNITHOPODA) FROM THE LATE CAMPANIAN CERRO DEL PUEBLO FORMATION, COAHUILA, MEXICO

Abstract A new lambeosaurine hadrosaurid, Velafrons coahuilensis, is described as the first lambeosaurine from the Cerro del Pueblo Formation of Coahuila, Mexico, and the first lambeosaurine genus to be named from North America in more than 70 years. Although the holotype specimen is a juvenile individual—as evidenced by its incomplete crest development and relative size compared to other North American lambeosaurines—ontogeny independent autapomorphies have been identified including quadrate with narrow quadratojugal notch and a postorbital with well developed, dorsally positioned squamosal process. Additionally, this taxon is unique in that the prefrontal is not dorsally deflected and anteroposteriorly expanded as in other lambeosaurine taxa of its size, but rather retains the frontal-prefrontal “clamp” present in smaller individuals of other taxa. Phylogenetic analysis places Velafrons in a polytomy with numerous other fan-crested lambeosaurines. The crest structure of Velafrons more closely resembles that of Corythosaurus and Hypacrosaurus because it possesses an anteriorly projecting nasal process over the dorsal premaxilla process. Biogeographically, Velafrons is one of three distinct hadrosaurids known from approximately 73.5 Ma—two lambeosaurines and one hadrosaurine—all restricted to the southern region of the Western Interior Basin of North America.