Osteological, myological, and biomechanical investigations of the sauropod dinosaur Dreadnoughtus schrani and molecular paleontological investigation of the marine crocodile Thoracosaurus neocesariensis

Kristyn K. Voegele

doi:10.17918/etd-7628

Three of the four chapters of this dissertation address aspects of the biology of the dinosaur Dreadnoughtus schrani. Discovered in Patagonia, Argentina, the holotype skeleton of Dreadnoughtus is nearly complete, preserving 70% of its postcranial elements, including at least one of every major limb bone and at least one representative of each portion of the vertebral column. Dreadnoughtus, a titanosaurian sauropod dinosaur weighing 62.5 metric tons, is the most complete skeleton among the most massive titanosaurians yet discovered. The completeness of this giant provided a unique opportunity to thoroughly investigate the osteology of the dorsal vertebral series, appendicular myology, and elbow biomechanics of one of the largest animals to ever walk on land. Of the eight most massive titanosaurians described to date, Dreadnoughtus preserves the second most complete dorsal vertebral series, consisting of seven nearly complete vertebrae. One notable comparison of the dorsal vertebrae among some of the largest titanosaurians is a difference in the dorsoventral depth of the transverse processes: Dreadnoughtus and Futalognkosaurus possess dorsoventrally narrow transverse processes whereas Puertasaurus exhibits deep transverse processes. Though the dorsal vertebrae of Dreadnoughtus likely pertain to both the holotype and paratype individuals, they could be placed in a predicted serial sequence with minimal, if any, overlap. Specifically for Dreadnoughtus, this predicted sequence was based on several features, including: 1) division of the spinodiapophyseal laminae; 2) presence of the posterior centroparapophyseal laminae, and; 3) variable curvature of the postzygodiapophyseal laminae. Variation in curvature of the postzygodiapophyseal laminae is similar to the lamina "disconnection" described by Dr. Pablo Gallina in Bonitasaura. To date, only two appendicular myological reconstructions have been performed for titanosaurian sauropods: Neuquensaurus and Opisthocoelicaudia. Both of these taxa are significantly smaller and more derived than Dreadnoughtus, and thus exhibit more extreme wide-gauge posture (i.e., widening of the sacrum, beveling of the distal femoral condyles, etc.). The more basal phylogenetic position, large body size, and completeness of Dreadnoughtus allowed for the investigation of changes in muscle attachments in relation to body size and/or development of wide-gauge posture. The quality of preservation of the holotype and paratype skeletons of Dreadnoughtus allowed 76 osteological correlates to be identified as probable muscle attachments. Of the 53 muscles investigated, 49 were adequately supported to reconstruct at least one attachment and for 30 muscles to be assigned Level I or II Inferences (i.e., not Level I' or II' Inferences). Several titanosaurians preserve a raised osteological correlate on the medial side of the scapula corresponding to the origin of the M. subscapularis. This feature is present in titanosaurians of variable phylogenetic positions and body sizes. Additionally, only Dreadnoughtus and Giraffititan exhibit an accessory process ventrolaterally on the preacetabular lobe of their ilia. This location represents the attachment of the M. puboischiofemoralis internus II, a hind limb protractor and adductor. Development of this process may be related to increased stress imparted by the muscle in relation to wide-gauge posture. Using the attachment locations of the elbow flexor muscles (identified in this dissertation) and soft tissue data from extant archosaurs, I next investigated the kinematics of the elbow of Dreadnoughtus. The goal of this chapter was to modify a biomechanical method used to study human ankles, by Dr. Sorin Siegler and colleagues, for use with extinct organisms, using the elbow of Dreadnoughtus as a case study. The resulting method includes significant innovations relative to previous methods employed in biomechanical modeling of extinct animals, such as: 1) the ability to test assumptions of joint motion used in other modelling methods; testing the effect(s) of cartilage variation on joint kinematics, and; 3) a comprehensive validation protocol. Through development of this model, an important insight was made: the possible presence of a spherical anterior projection of cartilage on the distal humerus for articulation with the radius during flexion. Though the method developed herein used Dreadnoughtus as a case study, it can be applied to other extinct organisms and more complex joint systems to aid in understanding the biomechanics of extinct organisms. The studies mentioned above, and the vast majority of paleontological literature, depend on preservation and the quality of preservation of fossils. Fossilization and preservation have received considerable attention in the literature, but much is still unknown about influences on fossilization, especially at the tissue or molecular level. Thus, in the final chapter of my dissertation, I consider the preservation of the marine gavialoid crocodilian Thoracosaurus neocesariensis. Less is understood about the chemical processes involved in the fossilization of bone in marine environments as more studies have been conducted on terrestrial organisms. Studies, such as described herein, provide a means for comparison of factors influencing preservation at the tissue level. In this chapter, I investigated the possibility that endogenous collagen I might persist in a femur of this crocodilian. The specimen was excavated from the Hornerstown Formation at Rowan Fossil Quarry in Mantua Township, New Jersey. The surrounding sediment was rich in glauconite, representing a depositional environment not previously investigated for preservation of soft tissues and biomolecules. I recovered soft tissue structures morphologically consistent with vertebrate osteocytes from the femur of this crocodile, and conducted three independent assays (each run in triplicate) which support the preservation of endogenous collagen I. Soft tissues and biomolecules were previously thought rarely to persist in marine fossils because of the possibility of extensive hydrolysis; however a molecular investigation for collagen I by Dr. Johan Lindgren and colleagues on a marine fossil has opened the door to further molecular studies of specimens preserved in marine environments. My findings support and suggest that further investigations of marine fossils and glauconitic deposits are warranted and may be fruitful.

Osteological, myological, and biomechanical investigations of the sauropod dinosaur Dreadnoughtus schrani and molecular paleontological investigation of the marine crocodile Thoracosaurus neocesariensis

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Osteological, myological, and biomechanical investigations of the sauropod dinosaur Dreadnoughtus schrani and molecular paleontological investigation of the marine crocodile Thoracosaurus neocesariensis

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