THE AXIAL SKELETON OF THE DINOSAUR SUUWASSEA EMILIEAE (SAUROPODA: FLAGELLICAUDATA) FROM THE UPPER JURASSIC MORRISON FORMATION OF MONTANA, USA

Abstract:  Vertebrae of Suuwassea demonstrate an interesting combination of plesiomorphies and autapomorphies among known members of the Flagellicaudata. The cranial cervical vertebrae have proportions close to Diplodocus but resemble those of Apatosaurus except by having greatly reduced cranial and caudal spinozygapophyseal laminae. As a result, they have craniocaudally compressed, caudally positioned spinous processes excavated on all sides by fossae. The cranial thoracic vertebrae are again similarly proportioned as those of Diplodocus but are morphologically similar to those of Apatosaurus . The most distinguishing feature of Suuwassea caudal vertebrae are the short, amphiplatyan, distalmost 'whiplash' caudal vertebrae. These may be either a retention of or a reversal to the plesiomorphic sauropod condition because classic flagellicaudatan, biconvex distalmost caudals occur in the Middle Jurassic of England.     

The appendicular skeleton of Suuwasseaemilieae (Sauropoda: Flagellicaudata) from the Upper Jurassic Morrison Formation of Montana (USA)

Appendicular elements of the sauropod dinosaur Suuwasseaemilieae, from the Upper Jurassic Morrison Formation of Montana, USA, display a peculiar mix of autapomorphic and plesiomorphic features. While more similar in overall morphology to Apatosaurus than other flagellicaudatans, the coracoid of Suuwassea lacks the quadrangular shape of Apatosaurus. The humerus of Suuwassea bears a pronounced proximal tuberculum, a feature seen elsewhere only in saltasaurine titanosaurian sauropods. The rectangular proximal articular surface of the tibia is proportioned neither like Diplodocus nor Apatosaurus type specimens, although this region may be intraspecifically variable. The pes of Suuwassea possesses plesiomorphically elongate phalanges and a small, uncompressed ungual, unlike other flagellicaudatans except Dyslocosaurus. The localization of tooth marks on the pedal elements suggests that sauropod feet may have been singled out by scavengers, as has been noted for elephants.     

First report of Apatosaurus (Diplodocidae: Apatosaurinae) from the Cleveland-Lloyd Quarry in the Upper Jurassic Morrison Formation of Utah: Abundance,distribution, paleoecology,and taphonomy of an endemic North American sauropod clade

A cervical vertebra preserved at the famous and productive Cleveland-Lloyd Dinosaur Quarry in the Upper Jurassic Morrison Formation of Utah is that of an Apatosaurus, a sauropod dinosaur genus not previously recognized at the site and the first new dinosaur taxon identified at the site in years. The presence of Apatosaurus at a mudstone site dominated by other taxa, both theropod and sauropod, suggests a pattern of preservation within the Morrison Formation in which sites in fine-grained sediments yield dramatically uneven relative abundances of dinosaurs, with variable dominant taxa by site, compared with more time-averaged and attritional coarse-grained channel sandstone deposits. In addition, the continued demonstration of the wide-spread occurrence and abundance of Apatosaurus within the Morrison Formation, and the absence of its clade among diplodocid faunas on other continents, suggest that this group may have been endemic to North America during the Late Jurassic and that it may have originated there, though this is far from clear.     

Giants on the landscape: modelling the abundance of megaherbivorous dinosaurs of the Morrison Formation (Late Jurassic,western USA)

The ecosystem impact of megaherbivorous dinosaurs of the Morrison Formation would have depended on their abundance (number of animals per unit of habitat area) on the landscape. We constrain Morrison megaherbivore abundance by modelling dinosaur abundance in terms of carrying capacity (K), average body mass (ABM) and animal's energy needs. Two kinds of model are presented: ‘demand-side’ models that estimate K in terms of the aggregate energy demand of the dinosaur community, and ‘supply-side’ models that estimate K in terms of retrodicted primary productivity. Baseline values of K, ABM and energy needs for the models are further derived from comparisons with modern large herbivores, and from the composition of the megaherbivore fauna from a particular stratigraphic interval of the Morrison, but in all models a broad range of fractions and multiples of these baseline parameters are considered. ‘Best-guess’ estimates of Morrison megaherbivore abundance suggest an upper limit of a few hundred animals across all taxa and size classes per square kilometre, and up to a few tens of individuals of large subadults and adults.     

Cranial biomechanics underpins high sauropod diversity in resource-poor environments

High megaherbivore species richness is documented in both fossil and contemporary ecosystems despite their high individual energy requirements. An extreme example of this is the Late Jurassic Morrison Formation, which was dominated by sauropod dinosaurs, the largest known terrestrial vertebrates. High sauropod diversity within the resource-limited Morrison is paradoxical, but might be explicable through sophisticated resource partitioning. This hypothesis was tested through finite-element analysis of the crania of the Morrison taxa Camarasaurus and Diplodocus. Results demonstrate divergent specialization, with Camarasaurus capable of exerting and accommodating greater bite forces than Diplodocus, permitting consumption of harder food items. Analysis of craniodental biomechanical characters taken from 35 sauropod taxa demonstrates a functional dichotomy in terms of bite force, cranial robustness and occlusal relationships yielding two polyphyletic functional ‘grades’. Morrison taxa are widely distributed within and between these two morphotypes, reflecting distinctive foraging specializations that formed a biomechanical basis for niche partitioning between them. This partitioning, coupled with benefits associated with large body size, would have enabled the high sauropod diversities present in the Morrison Formation. Further, this provides insight into the mechanisms responsible for supporting the high diversities of large megaherbivores observed in other Mesozoic and Cenozoic communities, particularly those occurring in resource-limited environments.     

Determination of accurate KI values for tight-binding enzyme inhibitors: an in silico study of experimental error and assay design

Determination of accurate K(I) values for tight-binding enzyme inhibitors is important from both a basic biochemistry point of view (understanding the differences in affinity of related molecules) and a medicinal chemistry vantage (developing structure-activity relationships (SAR)). It is advantageous to directly fit the quadratic equation describing tight-binding behavior, known commonly as the Morrison equation, to obtain these K(I) values. The results of simulated experiments that examine the effect of assay design and experimental error on the ability to accurately determine K(I) values at several [E]0/K(I-app) ratios are described. Input ("true") values of the uninhibited velocity, inhibition constant, and total enzyme concentration were used to calculate the velocity at various inhibitor concentrations. Gaussian error was introduced into the velocities and the simulated reactions were fit to estimate upsilon0, K(I), and [E]0. Recommendations for optimizing the inhibitor dilutions within the context of a 96-well-plate format and simple serial dilution steps are made. These include using three points to determine the enzyme concentration ([I]=0, 0.5[E]0, and [E]0), using a narrow dilution series with only two or three points to determine the asymptote at high inhibitor concentration, and avoiding fixing [E]0 to a constant value in the fitting if at all possible. The risks and rewards of fixing [E]0 to a constant value, especially the effect on SAR, are also examined.     

Taphonomy of Sheridan College Quarry 1, Buffalo, Wyoming: Implications for reconstructing historic dinosaur localities including Utterback's 1902-1910 Morrison dinosaur expeditions

The Upper Jurassic Morrison Formation has yielded some of the most important, voluminous and diverse dinosaur bonebeds in western North America, yet many of its historic sites were excavated during the celebrated period of vertebrate paleontology in western North America referred to as the first and second “Great Dinosaur Rush” (1870-1910s). Because of the large quantity of fossils collected during this era, a considerable amount of data pertaining to patterns of sedimentation, preservation, and paleoecology across broad portions of the Morrison Formation (and indeed many other Mesozoic and Cenozoic units) is still poorly understood. This paper critically re-evaluates the Sheridan College Quarry 1 dinosaur bonebed which lies along the western rim of the Powder River Basin in the region of localities excavated during Utterback's expeditions in the 1900s. Sedimentologically, the bonebed is interpreted as having been formed by episodic flooding events affecting the proximal floodplain depocenter of a meandering river system. Limited evidence of bone abrasion or rounding and progressive upsection changes in bone orientations suggest that minimal transport occurred, but that at least four episodes of overbank flooding resulted in the concentration and burial of attritional, time averaged vertebrate skeletal material that accumulated in topographic lows on the floodplain. Taphonomic analysis indicates that multiple unassociated to partially associated fossil elements excavated represent at least three taxa of sauropod dinosaurs, whereas isolated elements from the site indicate the presence of several other small vertebrate taxa. This work provides significant new information not only about the Sheridan College Quarry 1, but also about local sedimentary and taphonomic conditions that were likely influential to burial and preservation of other nearby Morrison dinosaur localities in the Big Horn Mountains, most notably those excavated during the famous Utterback expeditions. This study highlights the research potential in reconstructing lost data for historic dinosaur localities.     

The oldest Cretaceous North American sauropod dinosaur

Sauropod dinosaurs have been found in sediments dating to most of the Cretaceous Period on all major Mesozoic landmasses, but this record is spatiotemporally uneven, even in relatively well-explored North American sediments. Within the 80 million-year-span of the Cretaceous, no definitive sauropod occurrences are known in North America from two ca. 20–25 million-year-long gaps, one from approximately the Berriasian–Barremian and the other from the mid-Cenomanian–late Campanian. Herein, we present an undescribed specimen that was collected in the middle part of the twentieth century that expands the known spatiotemporal distribution of Early Cretaceous North American sauropods, partially filling the earlier gap. The material is from the Berriasian–Valanginian-aged (ca. 139 Ma) Chilson Member of the Lakota Formation of South Dakota and appears to represent the only non-titanosauriform from the Cretaceous of North America or Asia. It closely resembles Camarasaurus and may represent a form closely related to that genus that persisted across the Jurassic–Cretaceous boundary.     

Probable crocodilian tracks and traces from the Morrison Formation (Upper Jurassic) of eastern Utah

A tetradactyl pes impression and tridactyl manus impression are described as the type specimen of Hatcherichnus sanjuanensis ichnogen. et ichnosp. nov., a probable large crocodilian ichnite from the Salt Wash Member of the Upper Jurassic Morrison Formation in eastern Utah. A similar pes track from the Morrison Formation at Garden Park, Colorado, may also belong to this ichnogenus. The type specimen from Utah consists of plaster replicas of natural casts of a left pes impression and a left manus impression. Associated with the type specimen were possible tail and body drag impressions. The tracks do not appear to be part of a walking trackway and may be swim tracks associated with an animal in shallow water. The tracks occur at a visible contact between slightly fining‐upward channel sandstone units.