The Vale Formation (Lower Permian) Its Vertebrates and Paleoecology

The Vale Formation is a wedge of predominantly terrestrial sediments of Leonardian age (Permian), overlying the Clear Fork Group and underlying the Choza Formation. Studies of the terrestrial vertebrates and stratigraphy of the Vale Formation, carried on since the late 19305, provide the basis for an initial synthesis of the faunas, stratigraphic distribution, paleoecology, taphonomy, and evolution of the vertebrates. Attention is focused on four principal outcrop areas: the northern Vale outcrop, with a complete section, largely in Knox County, Texas; the Sid McAdams locality, in the lower part of the Vale in southern Taylor County, Texas; the Blackwood locality, middle part of the Vale in central Taylor County, Texas; and the Stamford locality, middle part of the Vale in southern Haskell County, Texas. In addition, numerous other small sites in Texas and localities of equivalent age in Oklahoma were used in the analyses. Except for the northern Vale outcrops, the fossil vertebrate localities have been treated only briefly or not at all in previous publications. A study of fossil occurrences over a north-south distance of about 190 km in Texas, and of sections ranging up to 150 m thick, has provided a basis for tentative conclusions. The primary differences between the Vale and Arroyo faunas are the result of loss of genera and species in the upper part of the Arroyo Formation. New species were introduced early in the north and they, or their derivatives, appeared later to the south. Conditions of deposition pass from paralic in the south to strictly terrestrial with stream action predominant in the central and northern parts of the area. During deposition of the Vale Formation, especially in the north, climates were marked by increasing dryness and seasonality of rainfall. Most vertebrate remains were transported into the areas where they have been found. Only in ephemeral lakes and ponds were the organisms preserved where they lived. There is little evidence of pronounced evolutionary change during deposition of the Vale. Some speciation seems to have taken place, but faunal differences between areas were primarily related to climatological and physiographic differences. The fauna of the

Vale does not differ significantly from that of the overlying Choza Formation. The report brings together all available information on the Vale faunas. Firmer interpretations of the evolution of the faunas will become possible when wider chronological and spatial distribution of vertebrates is known and after additional stratigraphic and paleoecological field studies have been completed.