Master's Theses

Document Type

Thesis - campus only access

Date of Award

Fall 2002

Degree Name

Master of Science (MS)

Department

Geosciences

Advisor

Richard Zawerksi

Abstract

Dinosaur material was collected from the upper Brushy Basin Member of the Morrison Formation (Jurassic) on Little Cedar Mountain in east-central Utah. The specimens came from a portion of the Brushy Basin that consists of a brittle mudstone and durable fine-grained sandstone inter-bedded with a nodular marl. Both elastic layers contained bones, which suggests that they were first deposited in sands then buried by mud of a fluvial system. Elements found include a fragmented sauropod and theropod tooth, a sauropod scapula, coracoid, femur, tibia, fibula, caudal vertebrae, ribs, pubis, and phalanx. The fragmented theropod tooth is from a large carnosaur believed to be an allosaur. No signs of scavenging or predation have yet been found. It is believed that these large theropods were constantly shedding teeth at each feeding. The sauropod tooth is from a camarasaur. This tooth is believed to have come from younger strata and was eroded down slope. Comparative studies of bone morphology show that the post-cranial elements closely resemble those of the genus Apatosaurus. The scapula, coracoid, fibula, femur, and caudal vertebrae are the most complete. Therefore, the taxonomic assignment was determined from these elements, primarily the caudal vertebrae. Several of the elements show signs of weathering. The coracoid and scapula show significant weathering on the side that was first exposed during excavation. This side was probably exposed to the air longer than the underside, which shows less damage due to weathering. It is quite possible that these bones were exposed for several years. Also, many bones show signs of flaking, which is another indicator that they were exposed for some time after deposition. Bone orientation and type suggest that the post-cranial elements represent one individual. Most of the bones were disarticulated with the exception of the five caudal vertebrae. The presence of asymmetric ripple marks in the sandstone, from which the sauropod bones were excavated, indicate a fluvial environment. Sauropod bones may have been scattered about by a combination of scavenging and fluvial processes along a flood plain.

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© 2002 David R. Schmidt

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