TAXONOMIC AND PROVENANCE ANALYSIS OF A LEGACY COLLECTION OF FOSSIL FISH BONES FROM LIVE OAK COUNTY, TEXAS

Prior to ~1980, hundreds of disarticulated fossil fish bones were collected from a uranium pit near Three Rivers, TX (Live Oak County), and added to the teaching and research collections of St. Mary’s University. This region of the South Texas Coastal Plain is covered by Tertiary sediments, but because of limited documentation, the exact collection location is not known. These fossils are potentially significant because of the scarcity of published reports of Tertiary fish from South Texas. Our study aimed to 1) determine the likely formation where these specimens were collected, 2) identify the fossils to the smallest taxonomic group using an apomorphy-based approach, and 3) estimate the minimum number of individuals (MNI) present.

To help determine a more precise location for the fossils, we collected samples of the Oligocene/Miocene Catahoula Formation and the Miocene Oakville Sandstone, the uranium-bearing units in Live Oak County, for grain analysis. Associated rock matrix was removed from the fossils and collected for comparison. The mineralogy of the matrix sample qualitatively matches reported mineralogy for the Oakville. A grain size analysis of the matrix sample, however, shows better agreement with the Catahoula. This difference may be due to sampling bias in that the fine fraction has been preferentially lost from the matrix samples, and is therefore not representative of the host rock formation.

The fossil sample includes hundreds of vertebrae, isolated ribs and several skull elements including hyomandibulae, edentulous maxillae, parasphenoids, basioccipitals, preoperculars, operculars, cleithrums, dentaries with teeth, angulars, and various pharyngeal elements with teeth. The pharyngeal elements with ankylosed teeth, edentulous maxillae, and hyomandibulae are characteristic of the Cypriniformes, a mostly freshwater group including carps, minnows, loaches, and their relatives. However, presence of dentaries containing teeth indicate that at least one other taxon is also represented in this sample. Element counts taken from the hyomandibulae, maxillae, and parasphenoids provide a MNI of 26. With few exceptions none of the bones are articulated but several delicate structures such as vertebral hemal arches and neural spines remain intact, suggesting minimal transport of the fossils.