Award Date

12-1-2013

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

First Committee Member

Stephen M. Rowland

Second Committee Member

Jean Cline

Third Committee Member

Ganqing Jiang

Fourth Committee Member

David Lee

Number of Pages

75

Abstract

In this study I describe and interpret tracks and trackways of the Jurassic Aztec Sandstone of southern Nevada and southern California. This study involved mapping of all known tracks and trackways, including foot length, stride length, and trackway width. Photogrammetric data, collected by Bureau of Land Management scientists, were utilized for several trackways in Red Rock Canyon National Conservation Area.

More than three hundred tracks belonging to five ichnotaxa were documented within the Aztec Sandstone, including about 165 tridactylGrallator, 250 tetradactyl (four-toed)Brasilichniumtracks, and 7 arthropod trackways ofOctopodichnusandPaleohelcura. Four of the five ichnotaxa were not previously reported from the Aztec Sandstone. The trackway finds are similar to the most common tracks found in the correlative Navajo Sandstone, although the diversity of tracks is much higher in the Navajo. One type of track examined in this study has not been reported from the Navajo Sandstone. The higher diversity within the Navajo is almost certainly partly due to the much longer history of systematic investigation. All but one of the discovered tracksites in the Aztec were unknown prior to October 2011.

Where possible, in the case of the Grallator trackways I calculated the speed of the trackmaker. Speeds range from 0.7 mph (0.35 m/sec) to 8.5 mph (3.8 m/sec). In one trackway, pauses in the animal's steps are also recorded. Several of the tracksites contain multiple ichnotaxa on the same bedding plane, and sometimes trackways of different ichnotaxa overlap each other. From details such as these, some aspects of the paleoecology of the Aztec Sandstone can be inferred. The Grallator trackmakers were carnivorous theropod dinosaurs, which probably preyed on the herbivorous Brasilichnium trackmakers. The Brasilichnium trackmakers fed on unknown plants. Some tracksites reveal evidence that the trackmakers resided near or visited the same area repeatedly over an extended period of time, which implies the sustained availability of food.

Keywords

Arthropod; Aztec Sandstone; California; Dinosaur tracks; Footprints, Fossil; Grallator; Gregarious; Ichnology; Jurassic Geologic Period; Nevada; Paleoecology; Synapsid; Trackways

Disciplines

Ecology and Evolutionary Biology | Geology | Paleobiology | Paleontology

Language

English


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