Paleontological Fieldwork: 2013

Roland Springs Ranch Locality 1, an earliest Pleistocene fauna
from the Rolling Plains of Scurry County, Texas

Session: June 2nd - July 14th

Current research began in 2005 and for the 2013 season, fieldwork takes place at the Roland Springs Ranch Locality 1 (RSR-1). Lab work is carried out in the field camp to help facilitate the continuing research into the understanding of Pleistocene faunas and climates on the Southern Plains.

Physiographic Setting
Roland Springs Ranch is on the Rolling Plains just east of Snyder, Texas. A working ranch, the landscape generally is pristine away form the ranch buildings with minimal development of the ranchland. The landscape consists of rough terrain that is drained by numerous tributaries of the Brazos River system. The Clear Fork is a major tributary to the Brazos River that in turn has a number of smaller tributaries flowing into it. The Clear Fork runs through the property from the north to the east. RSR-1 is situated on Turtle Creek that is an ephemeral tributary to the Clear Fork of the Brazos River. The modern drainage has cut through over 1.9m (6.2ft) of loamy sand deposit to expose an ancient drainage and fairly dynamic history. A fluctuating water table is indicated at some time after the bones and sediments were deposited. At some point in the more recent past, an erosional channel (arroyo) was cut through the area in a north-south direction perpendicular to the modern drainage that flows from the northwest to southeast. The channel cut down through the surface soil almost to the gleyed deposits, where the Pleistocene bone bed is located, and then refilled within the last few hundred years. It indicates a very dry period, most likely a reflection of the Altithermal from about 6,500 to 4,500 years ago.

Previous Investigation
Exploration began in 2005 to assess the significance and potential of the locality and determine the association of the various taxa. RSR-1 has yielded the remains of over 50 taxa from a collection of over 12,000 specimens representing both large and very small (microvertebrate) animals from all classes (amphibians, birds, reptiles, mammals, and fish). Most notable among the large forms are the remains of the giant land tortoise (Hesperotestudo spp.), gazelle-horse (Nannipus peninsulatus), ancestral coyote (Canis lepophagus), North American cheetah-like cat (Miracinonyx cf. trumani), small pronghorn (Capromeryx spp.) and large birds such as an extinct turkey (Meleagris spp.), raptors, and a heron/crane (Ardeidae). The fauna indicates a riparian setting within a grassland environment, lacking seasonal extremes and perhaps with an increased moisture regime relative to today's continental climate. The taxa represented in the RSR-1 fauna suggest an approximate age for the locality of the earliest Pleistocene, 2.6 - 1.8 million years ago, within the Blancan Land Mammal Age. Localities of this age are uncommon in Texas and throughout the continent.

2013 Fieldwork
Fieldwork for the 2013 season at RSR-1 focuses on both excavation and geological exploration. Excavation continues in the Locality 1 bone bed to trace the eroded contact of the underlying sedimentary unit. Distinctive in color, this unit, most likely is Pliocene in age, represents the eroded, oxidized surface of an ancient stream bed within which the faunal material was deposited by later fluvial actions. Additional geological and geomorphological investigations involve landscape development and sediments in the Clear Fork drainage across the ranch.

The regional goal is to understand the dynamics of the interface of grassland faunas and climate reflected in adaptive responses and climatic change detected in the paleontolgical record. The current objective is to establish the past Pleistocene animals, environment, and climate of the region and secure a better age estimate of the locality.

Methodology

Field. Primary components of the fieldwork consist of:

- Hand excavation of 1m X 1m units in 10cm levels and 2.5cm sublevels within the defined stratigraphy;
- Recording, mapping, and photographing of material found in situ;
- Recovery of micromaterials from provenienced sediments by water washing through nested fine-mesh screen;
- Fragile bone stabilized initially in the field with conservation grade resin solution prior to removal;
- Plaster jacketing employed for very fragile large specimens;
- Use of standardized Museum forms to record all information.

Laboratory. The on-site lab involves all crew members checking in objects, crosschecking of field forms, collections organization, and sorting of all resultant concentrates from the water washing of excavated sediments. All recovered objects and documentation will be transported to the Landmark's Quaternary Research Center (QRC) for additional processing and analysis. Processing entails accessioning, cleaning, identification, stabilization as necessary, cataloging, bar-coding, data inputting, inventory, and packaging.