Dinosauria

The anatomy and systematic position of the theropod dinosaur Chilantaisaurus tashuikouensis Hu, 1964 from the Early Cret. of Alanshan, China

dinosauria — Tue, 16 Sep 2008 10:02:44 GMT

There is little consensus on the systematic position of the colossal theropod dinosaur
Chilantaisaurus tashuikouensis from the Cretaceous (Aptian–?Albian or Upper Cretaceous)Ulansuhai Formation of Inner Mongolia, which has been recovered as a derived member of both Allosauroidea and Spinosauroidea by numerical phylogenetic analyses. Redescription of the type material of C. tashuikouensis reveals an unusual combination of morphological features that render determination of its systematic position problematic. It possesses anatomical features that have been proposed as synapomorphies of Neotetanurae: a preacetabular fossa on the ilium, and a wedge-shaped crosssection of the shaft of the third metatarsal. It also shares some features with specific allosauroid taxa: a pronounced ulnar epicondyle on the humerus, and a prominent medial shelf bounding the preacetabular fossa on the ilium (also present in tyrannosauroids). However, it lacks some features that are present in all other allosauroids: a marked depression on the anterior surface of the distal humerus adjacent to the ulnar condyle, and a humerus that is less than 0.4 times the length of the femur; it
furthermore possesses a tibial astragalar facet that is approximately 10 % of the tibial length, which suggests a more basal position within Tetanurae. Chilantaisaurus shares certain features with some spinosauroids: an enlarged and elongated first manual ungual, and a suprastragalar buttress that has been modified to a vertical ridge, but these characters are not unique to spinosauroids. Ahighly reduced fourth trochanter may be an autapomorphy of Chilantaisaurus, as has previously been suggested, or unite the taxon with Coelurosauria in an entirely novel grouping. On the basis of these observations it
is likely that Chilantaisaurus is a neotetanuran, but unlikely that it is an allosauroid. Chilantaisaurus may belong to an alternative lineage of very large theropods that continued into the Cretaceous from the diversification of basal neotetanurans during the Middle Jurassic.

Manual ungual I of Chilantaisaurus tashuikouensis (IVPP V.2884.2): (a) lateral view; (b) medial view; (c) proximal view. Scale bar = 100 mm.

Body size evolution in Mesozoic birds: little evidence for Cope’s rule

dinosauria — Tue, 16 Sep 2008 09:59:16 GMT

Cope’s rule, the tendency towards evolutionary increases in body size, is a long-standing macroevolutionary generalization that has the potential to provide insights into directionality in evolution; however, both the definition and identification of Cope’s rule are controversial and problematic. A recent study [J. Evol. Biol. 21 (2008) 618] examined body size evolution in Mesozoic birds, and claimed to have identified evidence of Cope’s rule occurring as a
result of among-lineage species sorting. We here reassess the results of this study, and additionally carry out novel analyses testing for within-lineage patterns in body size evolution in Mesozoic birds. We demonstrate that the nonphylogenetic methods used by this previous study cannot distinguish between among- and within-lineage processes, and that statistical support for their results and conclusions is extremely weak. Our ancestor–descendant within-lineage analyses explicitly incorporate recent phylogenetic hypotheses and find little compelling evidence for Cope’s rule. Cope’s rule is not supported in Mesozoic birds by the available data, and body size evolution currently provides no insights into avian survivorship through the Cretaceous–Paleogene mass extinction.

‘Supertree B’ of Mesozoic birds demonstrating inter-relationships, the five major clades (Aves, Pygostylia, Ornithothoraces, Enantiornithes, and Ornithuromorpha) used in the analyses, and inferred branch lengths. Note that the majority (60%) of taxa included in
the supertree are from just two formations: the Yixian Formation (late Barremian–early Aptian) and the Jiufotang Formation (Aptian) of China. The same bias is present in the nonphylogenetic data set of Hone et al. (2008), see Fig. 2. ‘Supertree A’ (19 taxa) differs in that there is no resolution of relationships within the clade labelled ‘X’ (which also includes the taxon Eoalulavis from the Yixian Format

Superiority, Competition, and Opportunism in the Evolutionary Radiation of Dinosaurs

dinosauria — Tue, 16 Sep 2008 09:56:02 GMT

The rise and diversification of the dinosaurs in the Late Triassic, from 230 to 200 million
years ago, is a classic example of an evolutionary radiation with supposed competitive
replacement. A comparison of evolutionary rates and morphological disparity of basal dinosaurs and their chief “competitors,” the crurotarsan archosaurs, shows that dinosaurs exhibited lower disparity and an indistinguishable rate of character evolution. The radiation of Triassic archosaurs as a whole is characterized by declining evolutionary rates and increasing disparity, suggesting a decoupling of character evolution from body plan variety. The results strongly suggest that historical contingency, rather than prolonged competition or general “superiority,” was the primary factor in the rise of dinosaurs.

Phylogenetic relationships and morphospace occupation for Triassic archosaurs. (A) Framework phylogeny for Triassic crurotarsans (13) scaled to the Triassic time scale (13). Numbers at top refer to millions of years before present; gray bars represent the observed durations of major lineages; vertical dashed lines denote two hypothesized extinction events (CNEE and TJEE); arrowheads indicate lineages that survived the TJEE. Lad, Ladinian; Crn, Carnian; Rh, Rhaetian; EJ, Early Jurassic. (B) Empirical morphospace for Triassic archosaurs, based on the first two principal coordinates (13). Large circles, dinosaurs; ovals, pterosaurs; squares, poposauroids; hexagons, phytosaurs; stars, aetosaurs; crosses,
crocodylomorphs; smaller solid circles, “rauisuchids”; larger solid circles, nondinosaurian dinosauromorphs, Scleromochlus.

Three-dimensional geometry of a pterosaur wing skeleton, and its implications for aerial and terrestrial locomotion

dinosauria — Thu, 11 Sep 2008 12:50:00 GMT

This study reports on the three-dimensional spatial arrangement and movements of the skeleton of Anhanguera santanae (Pterodactyloidea: Ornithocheiridae), determined using exceptionally well-preserved uncrushed fossil material, and a rigid-body method for analysing the joints of extinct animals. The geometric results of this analysis suggest that the ornithocheirids were inherently unstable in pitch and yaw. As a result, pitch control would
probably have been brought about by direct adjustment of the angle of attack of the wing, by raising or lowering the trailing edge from the root using the legs if, as is indicated in soft-tissue specimens of a number of unrelated pterosaur species, the legs were attached to the main wing membrane, or by using long-axis rotations at the shoulder or wrist to raise and lower the trailing edge from the wingtip. An analysis of the three-dimensional morphology of the wrist lends support to the idea that the pteroid – a long, slender wrist bone unique to pterosaurs that supported a membranous forewing – was directed forwards in flight, not towards the body. As a result, the forewing could have fulfilled the function of an air-brake and high-lift device, and may also have had an important role in pitch, yaw, and roll control. The joint analysis is consistent with a semi-erect quadrupedal model of
terrestrial locomotion in the ornithocheirids.

Anhanguera santanae

Adaptive Features of Protoceratopoids (Ornithischia: Neoceratopsia)

dinosauria — Thu, 11 Sep 2008 12:42:28 GMT

The analysis of some morphological characteristics of protoceratopoid skeletons, the extent of mobility of the vertebral column, and the probable adaptive significance of these features suggest that Bagaceratops had a mostly aquatic mode of life, Protoceratops was semiaquatic, Udanoceratops was facultatively aquatic, and Leptoceratops was predominantly terrestrial. Protoceratopoids were quadrupeds, with the prevalence of hind limbs, probably using slow or rapid trotlike gait. An asymmetrical locomotion was most likely impossible. On dry land, Bagaceratops and Protoceratops moved slowly. Udanoceratops and Leptoceratops
approximately equally used rapid and slow locomotor modes, although the second could run for a longer time than the first.

Schemes of cross section through the middle part of the tail: (a–d) reconstruction of tail section at 12–15cd: (a) Bagaceratops, (b) Protoceratops, (c) Udanoceratops, (d) Leptoceratops, (e) Alligator mississippiensis, at 21cd (after Frey, 1988, text- figs. 46c, 60c), and (f) Megalobatrachus japonicus, at 11cd. Designations: oblique lines show epaxial muscles, crossing lines are hypaxial muscles, dots are adipose tissue. All figures are given in equal heights of vertebral centers.

PROBABLE GUT CONTENTS WITHIN A SPECIMEN OF BRACHYLOPHOSAURUS CANADENSIS (DINOSAURIA: HADROSAURIDAE) FROM THE UPPER CRETACEOUS FROM MONTANA

dinosauria — Thu, 11 Sep 2008 12:39:16 GMT

An exceptionally preserved subadult specimen (JRF 115H) of a hadrosaurid, Brachylophosaurus canadensis, from the Judith River Formation near Malta, Montana, contains abundant plant fragments concentrated within the body cavity. We examined the taphonomy of the carcass and analyzed the gut-region material to test whether the organic remains represent fossilized gut contents. The dinosaur was buried in a fluvial channel setting, and the excellent articulation, integument impressions, and lack of scavenging indicate rapid burial. The organic material occupies a volume of at least 5750 cm3, and
comparable material is not found outside the carcass. The carcass contents include 63% clay, 16% undetermined matrix, 12% organic matter, and 9% larger inorganic clasts—mostly 50–100 m quartz grains. Most of the organics appear to be mm-scale leaf
fragments. The most parsimonious explanation for the presence and composition of the gut-region material is that much of the plant fossils represent reworked brachylophosaur ingesta influenced by flowing water that entered through openings in the carcass and introduced clay. The evidence strongly suggests that the hadrosaurid ate significant quantities of leaves and processed them into small pieces. This study provides baseline information for analyzing other cases of putative gut contents in herbivorous dinosaurs.

Brachylophosaur specimen JRF 115H and its discovery site. A) JRF 115H in situ. Arrow indicates block of caudal vertebrae separated from the rest of the specimen by a small wash. Matrix is fine-grained sandstone. Black bar is 25 cm long. Photograph taken by Mark Thompson. B) Skeletal map of JRF 115H, made during excavation by Greg Wenzel. Each square is 25 cm long on a side. C) JRF 115H after preparation to indurated matrix with person for scale. Indurated matrix (white arrow) is more yellowish in color and more indurated than other remaining matrix (black arrow).

A NEW GENUS AND SPECIES OF CAUDIPTERID DINOSAUR FROM THE LOWER CRETACEOUS JIUFOTANG FORMATION OF WESTERN LIAONING, CHINA

dinosauria — Wed, 27 Aug 2008 07:33:22 GMT

A new oviraptorosaur, Similicaudipteryx yixianensis gen. et sp. nov. is described from the Jiufotang Formation (120 Ma) of the Jehol Group in western Liaoning, China, which is referred to the Caudipteridae based on a dagger-like pygostyle and the shape of the ilium that are most similar to those of Caudipteryx. It differs from other oviraptorosaurids in that the ratio of pubis to ilium length is 1. 46 and the presence of two large and deep hypapophyses on dorsal vertebrae. The known caudipterids have previously been found only from the Jianshangou Member of the Yixian Formation (125 Ma) of the Sihetun area in Liaoning Province. S. yixianensis represents the first caudipterid dinosaur from the Jiufotang Formation. The new discovery provides more information for the discussion of the evolution of oviraptorids during the Early Cretaceous and adds to the dinosaur assemblage of the Jehol Biota.

Holotype of Similicaudipteryx yixianemis gen. el sp. nov. ( IVPP V 12556) Abbreviations: Cav. caudal vertebra; Cr. cervical rib; Cv. cervical vertebra; Dv. dorsal vertebra; Fe (1). left femur; Fe ( r) . right femur; Fi ( 1). left fibula; Hs. haemal spine; Hu ( 1). left humerus; II ( I ) . left ilium; II ( r ) . right ilium; Mt 1-IV. metatarsals I-IV; Pd I-IV. pedal digits I-IV; Py. pygostyle; Ps. pubic symphysis; Pu. pubis; Sc ( 1). left scapula; St. sternum; Sv. sacral vertebra; Ti ( 1). left tibia; Ti ( r) . right tibia

Polar dinosaurs on parade: a review of dinosaur migration.

dinosauria — Wed, 27 Aug 2008 04:58:41 GMT

Cretaceous polar dinosaur faunas were taxonomically diverse, which suggests varied strategies for coping with the climatic stress of high latitudes. Some polar dinosaurs, particularly larger taxa such as the duckbill Edmontosaurus Lambe, 1917, were biomechanically and energetically capable of migrating over long distances, up to 2600 km.
However, current evidence strongly suggests many polar dinosaurs (including sauropods, large and small theropods, and ankylosaurs of New Zealand) overwintered in preference to migration. Certain groups also appear more predisposed to overwintering based on their physical inability (related to biomechanics, natural history, or absolute size) to migrate, such as ankylosaurs and many small taxa, including hypsilophodontids and troodontids. Low
nutrient subsistence is found to be the best overwintering method overall, although the likelihood that other taxa employed alternative means remains plausible. Despite wide distribution of some genera, species level identification is required to assess the applicability of such distributions to migration distances. Presently, such resolution is not available or contradicts the migration hypothesis.

Size dependent anatomy of migration. Although dinosaurs lacked the specific efficient mechanisms in the mammalian limb, they may have benefited energetically by simply being larger. A longer stride length and more upright limb posture in a 13 m long Edmontosaurus, in comparison with the caribou, meant it could cover the same distance while potentially using less energy relative to body mass.

A new titanosaurian braincase from the Allen Formation (Campanian–Maastrichtian), Rı´o Negro Province, Patagonia, Argentina

dinosauria — Tue, 19 Aug 2008 17:26:56 GMT

We describe a new titanosaurian braincase (MML-194), from the Upper Cretaceous (middle Campanian–lower Maastrichtian) of Río Negro Province, Argentina. Among titanosaurs, this specimen resembles Bonatitan reigi, more than any other member of the clade; the similarity is based on the supraoccipital protuberance bearing a median groove (also present in Saltasaurus and Rapetosaurus), the prominent basal tubera, the exit for the nerve VII located on the prootic crest, the occipital condyle and the foramen magnum almost of the same width. This material allows to observe some internal structures that are not appreciable in other titanosaurs, such as the pituitary cavity, the dorsum sellae and the foramen for the passage of the internal carotids, among other characters. The specimen MML-194 and Bonatitan were exhumed of same geological unit, the Allen Formation, from which have also been collected fossil eggs assignable to sauropods (megalooliths), for what is not unlikely that some of these taxa has been responsible of the laying of those eggs.

Titanosaurian braincase (MML-194)

Stegosaurian skin impressions from the Upper Jurassic Shangshaximiao Formation, Zigong, Sichuan, China: A new observation.

dinosauria — Thu, 14 Aug 2008 16:28:44 GMT

A skin impression fossil of Gigantspinosaurus sichuanensis was found in the Upper Jurassic Shangshaximiao Formation in Zigong, Sichuan. The fossil, preserved on the dorsal face of the left shoulder, clearly shows scales of Gigantspinosaurus sichuanensis. These scales are generally arranged as a net, and most of them are pentagonal, a few being quadrilateral and hexagonal. The maximum inner radius of most scales range from 5.7 to 9.2 mm. The scales are connected with each other by grooves. Scattered within small scales are a few pentagonal or hexagonal large scales, with each large scale surrounded by 13—14 scales. The surface of the scales is rough with string—like ridges. The stringy ridge on the scales made the surface of the scales uneven and thus may reduce the glare caused by reflected light. Based on the primary burial location and distribution of the scales, the authors believe that the skin impression fossil of Gigantspinosaurus sichuanensis is from the elbow of the forelimb, relevant upper arm and lateral area of the body.

Skin impressions of Gigantspinosaurus sichuanensis