Goal

Examine the species-level composition of two wet-interval floras from the Early Permian of North-Central Texas

Questions

1. Are the dominant xeric (dry) and hydric (wet) taxa different between floras?

2. How does the taxonomic diversity differ between floras?

3. What are the taphonomic differences between the two sites?

Introduction

• The Early Permian, 270-300mya, saw a gradual warming of the Earth, starting with polar ice and ending with ice-free poles

• The climate fluctuated glaciers waxed and waned, but there is little resolution of the finer details of these climate swings

• The rock record in lower latitude ice free area (“far-field”) have provided more detailed resolution of glacial patterns for the Pennsylvanian (ie, cyclothems)

• The far-field rock record of the Permian differs greatly and does not have as great resolution; however, the paleobotanical record records intercalations of dry-adapted floras and wet-adapted floras, possibly driven by climate fluctuations related to polar ice fluctuations.

Background

• Floras from the early Permian of Texas exhibit oscillations between xeric (dry) and hydric (wet) floras

• There are floras that both xyric/hydric elements; two from the lower-to-middle Waggoner Ranch Formation are:

• “Farmer Tank” collected by DiMichele & Chaney 1991

• “Cattle Tank” collected by Mamay & Watt 1974

• These two floras are from slightly different stratigraphic levels in the same rock outcrop, and represent different time intervals.

• Paleosol data (Tabor and Montanez) suggests a slightly wetter interval at this point, during an overall trend from cooler/wetter to hotter/dryer

Materials/Methods

• Floras were scanned using a hand lens/microscope and characterized in terms of taxonomic composition.

• Composition was assessed using the “quadrat method” of Pfefferkorn, Mustafa, and Hass (1975)

• Each hand sample was treated as a sampling quadrat; taxa on that quadrat were noted as present/absent, regardless of size/number of individual specimens present.

• Each quadrat represents both surfaces of a given hand sample

• Quadrat/hand-sample size was assessed roughly by making two orthogonal axis measurements in order to:

• Compare quadrat size to taxonomic richness

• Compare total surface area between the two floras

Most Common Plant Taxa

A. Cattle Tank is dominated by xeric (dry) taxa, most prominately Walchian conifers B. Farmer Tank is mixed, with Pecopteris as the dominant hydric (wet) taxa and Walchia and Russelites as the dominant xeric taxa. C. Prominent hydric taxa- Pecopteris, Sphenophyllum- are present at both sites. D. Prominent xeric taxa are more variable- Walchia sp.2 is absent from Farmer Tank, and Russelites is absent from Cattle Tank

Site Comparison
A. Farmer Tank has larger quadrats with higher density of organic material, and more fragmentary material B. Cattle Tank consists of smaller quadrats with mostly single specimens C. Cattle Tank contains shark teeth and bivalves which are absent in Farmer Tank, suggesting a different environment of deposition

Summary

The Floras from Cattle Tank and Farmer Tank are significantly different
Overall taxonomic diversity, based strictly on foliage/diagnostic stem material, is almost the same- 23 in Farmer Tank, 24 in Cattle Tank
Taphonomy between the sites is different (For quadrat size and density of organic material)

Acknowledgments

Thanks to the Smithsonian Office of the Director for funding the senior author's participation in the Research Training Program and to Cindy Looy for assistance with conifers and figures.