Gee et al.—New early Permian vertebrate locality 92(6):1092–1106
Table 1. Major previously described early Permian vertebrate localities within the Vale Formation of Texas. The northern Vale localities described by Olson (1948) pertain to numerous sites spanning the entire stratigraphic section of the Vale.
Locality County Position
Northern Vale Knox Sid McAdams Taylor Blackwood Stamford
Haskell middle Taylor middle Primary reference
lower−upper Olson (1948) lower
Wilson (1953); Mead (1971) Olson and Mead (1982)
Dalquest and Mamay (1963)
the co-occurrence of well-known early Permian tetrapods (Tri- merorhachis, Diplocaulus, Seymouria Broili, 1904, Dime- trodon) but stated that this material did not contribute novel information regarding these taxa (Wilson, 1953, p. 456) and thus did not describe, discuss, or figure any of this material. The locality’s tetrapod fauna, which includes an unusually dense assemblage of Dimetrodon specimens, was redescribed in an unpublished master’s thesis (Mead, 1971) that was incorporated into a summary of comparative Vale paleontology by Olson and Mead (1982). Material of T. insignis Cope, 1878 was collected from the same property but from a slightly younger horizon within the Vale Formation and was described by Olson (1979a). A large, nearly monotaxic assemblage of Diplocaulus was described by Dalquest and Mamay (1963) from the property of V.B. Rowland near Stamford (Jones County). Additionally, a new locality on the property of L.A. Blackwood near Buffalo Gap (Taylor County) was discovered in 1970 by David Berman and was described by Olson and Mead (1982). Brief lithological notes and faunal lists of less productive localities from the lower Vale (Baylor County) and the middle to upper Vale (Knox County) formation were compiled by Olson (1958). Since then, no new vertebrate localities have been reported, and general work on the tetrapod taxa has been extremely limited (e.g., Hunt and Lucas, 2005; Lucas and Hunt, 2005; Modesto et al., 2014). The ambiguity associated with some localities within the Clear Fork Group, particularly the Cacops Bone Bed from which the dissorophid Cacops aspidephorus Williston, 1910a, the caseid Casea broilii Williston, 1910b, and the varanopid Varanops brevirostris Williston, 1914 are known, and which occurs at either the top of the Arroyo Formation or at the bottom of the Vale Formation (Olson, 1989), suggests that material from the latter might have been collected prior to the WPA project, but none is confidently or explicitly referred to in the literature. Here we describe the faunal assemblage of a vertebrate-
bearing locality (Mud Hill) from the Olhausen Estate near Abilene, Texas (Taylor County) that occurs within the lower to middle Vale Formation (Figs. 1, 2). The locality is ~ 30km north of the Patterson locality described by Wilson (1953). This site has been previously referenced in the locality details of two publications regarding a nearly complete varanopid (e.g., Reisz and Tsuji, 2006; Campione and Reisz, 2010) but has never been formally presented with an overview of the geology and the broader vertebrate assemblage. The assemblage includes some of the common early Permian forms (e.g., Diplocaulus) but is most notable for the absence of typical early Permian taxa (e.g., Dimetrodon, temnospondyls), for the presence of rare clades (e.g., diadectids, Varanops), and for the sole occurrence of some clades (e.g., recumbirostrans) within the Vale Formation. This unusual taxonomic composition and various aspects of the
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Figure 1. Mud Hill locality map. 1, 2, 3=dig sites D1, D2, and D3; dotted lines=trails; unshaded area=exposure of the underlying Permian Vale Formation (Pvf); vertical striped area=Quaternary alluvium deposits (Qal); X=measured section site.
depositional environment, such as the articulation of much of the varanopid skeleton and the rarity of fully aquatic taxa commonly found in early Permian floodplain deposits, suggest in-situ preservation in an ephemeral aquatic setting. The description of this unusual assemblage contributes additional data regarding the Vale Formation, which is less well- characterized than the older Arroyo Formation, provides new insights regarding the paleobiology and the evolutionary history of forms that were previously rare or unknown from the for- mation, and permits the updating of the faunal list for the entire Vale Formation for the first time in 35 years.
Geologic setting
The Vale Formation is early Permian (Leonardian) in age and is exposed along a roughly northerly trend through central Taylor County, Texas. In southern Taylor County, the Vale is truncated by a major unconformity that separates Permian strata from the Cretaceous strata of the Callahan Divide. The Callahan Divide (trending west to east) is composed of the Antlers Sandstone at its base and is capped by the Edwards Limestone. A deposit of alluvium (Quaternary) extends to the north, from the Callahan Divide, and was laid down directly on the underlying Permian Strata by northward flowing streams. The alluvium thins to the north, and in many areas has been eroded away. In western Taylor County, the Vale Formation is overlain by the Choza Formation, which in turn is truncated by the same unconformity that truncated the Vale Formation to the east. In eastern Taylor County, the underlying Arroyo Formation is exposed where it has been truncated by the unconformity. The Vale Formation is exposed in road cuts, streams, and
along many hillsides in the exposure area. Although the bulk of the Vale Formation could be considered monotonous red shale, there is some diversity in its deposits, especially south of the Mud Hill locality (described below). A small channel deposit composed of fine to medium plane-bedded quartz sand is found in one such exposure. The bounding shales at this locality have been known to produce fragmented plant impressions. A more productive fossil plant locality is found further to the west and has been known to produce several different plant species and
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