Gee et al.—New early Permian vertebrate locality 92(6):1092–1106
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merit referral to Diadectes sp.; the same assignment was utilized in the histological sampling of this material by LeBlanc and Reisz (2013).
Class Synapsida Osborn, 1903 Clade Eupelycosauria Kemp, 1982
Family Varanopidae Romer and Price, 1940 Genus Varanops Williston, 1914
Type species.—Varanosaurus brevirostris Williston, 1911 from the Arroyo Formation, Texas, by subsequent designation (Williston, 1914).
Varanops brevirostris (Williston, 1911)
1911 Varanosaurus brevirostris Williston, p. 85, pls. 1–13. 1914 Varanops brevirostris Williston, p. 387.
Holotype.—Nearly complete skull with mandibles and articu- lated skeleton (FMNH UC 644) from the Arroyo Formation, Texas (Williston, 1911, pls. 1–13).
Figure 10. Diadectes sp. indet., upper jaw (premaxilla and maxilla) (TMM 43628-2): (1) dorsal profile; (2) lateral profile. Scale bar=2 cm.
Description.—Diagnostic material referable to the genus is limited to a right premaxilla articulated with a partial maxilla and associated with a pair of dentaries (TMM 43628-2), which are referred to the genus on the basis of the tooth count and mandibular morphology. The maxilla features a concave dorsal margin and a mostly flat ventral margin that is upturned only at the posterior region. The lateral surface is irregularly orna- mented in small pits and shallow grooves. Four tooth positions are present in the premaxilla, two with partial incisciform teeth in place. The incisiform teeth found in diadectids typically fea- ture cusps, but the teeth here are broken off at the level of the jaw. A slight decrease in size posteriorly is noted. Eleven tooth positions are present on the maxilla, which informs its taxo- nomic identification; most other diadectids possess 12 (e.g., Orobates Berman et al., 2004). Only the vacant sockets for the anterior molariform teeth are preserved, but they are compressed into oval cross sections, as in diadectids. The posteriormost teeth are weathered but preserve the general cusped morphology (Fig. 10.2). The tooth sockets increase in width to the seventh position and then decrease posteriorly. Another dentary (TMM 43628-3) was histologically
sampled in a study of dental tissues by LeBlanc and Reisz (2013). Both specimens are from the D1 site and thus indicate the presence of at least two individuals, as with the humeri.
Remarks.—The specific identity of the diadectid material is unresolved, as all previous material recovered from the Vale Formation was undiagnostic below the genus (and in some cases might not even warrant referral below the family level). Olson (1956c) suggested possible affinities of this material with Dia- dectes tenuitectus Cope, 1896, the highest occurring taxon at the time, but the extent of faunal overlap at the specific level between the Vale and the Choza formations remains poorly defined, and the material described here is only sufficient to
Description.—Material of Varanops from the locality has been previously described with a focus on scavenging of the post- crania of a large, nearly complete skeleton (TMM 43628) from the D2 site by Reisz and Tsuji (2006), and in greater detail in the description of the same specimen (referred to asTMM43628-1) by Campione and Reisz (2010) in a broader review of V. brevirostris. The cranial material comprises a partial skull with a braincase and associated mandible. The postcranial ske- leton consists of both humeri, an ulna, a complete femur and one comprising the distal and proximal ends, both tibiae, the pec- toral girdle (interclavicle, partial clavicles, and scapulacor- acoid), the pelvic girdle (pubis, ilia, and ischia), vertebrae from all major regions (cervical, thoracic, lumbar, sacral, and caudal), ribs, gastralia, and portions of the left manus and left pes. All materials pertaining to this specimen were figured and described in detail by Campione and Reisz (2010).
Remarks.—The revised osteology by Campione and Reisz (2010) was primarily based on the Mud Hill specimen, and no new information is contributed here.
Discussion
Depositional environment and paleoenvironment at Mud Hill.—The geology and paleoenvironmental interpretations of the Vale Formation have been frequently discussed in descriptions of vertebrate taxa (e.g., Olson, 1948; Wilson, 1953), but more extensive discussions have also been pre- sented by Olson (1958) and were well-summarized by Nel- son et al. (2013). The red shale facies (Fig. S1.1) is interpreted as alluvial plain deposits resulting from the set- tling of suspended clay from shallow overbank sheet floods. The absence of well-developed laminations and of varves suggests that perennial lacustrine deposition can be ruled out. The red color strongly supports the early oxidation of clay and indicates prolonged subaerial exposure. Diagenesis associated with early oxidation of the clays results in the
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