Journal of Paleontology, 92(6), 2018, p. 1092–1106 Copyright © 2018, The Paleontological Society 0022-3360/15/0088-0906 doi: 10.1017/jpa.2018.26


Faunal overview of the Mud Hill locality from the early Permian Vale Formation of Taylor County, Texas


Bryan M. Gee,1 Steven J. Rosscoe,2 Diane Scott,1 Judie Ostlien,3 and Robert R. Reisz1


1Department of Biology, University of Toronto Mississauga, Ontario L5L 1C6, Canada ⟨bryan.gee@mail.utoronto.ca⟩⟨diane.scott@utoronto.ca⟩ ⟨robert.reisz@utoronto.ca⟩ 2Department of Geology, Hardin-Simmons University, Abilene, Texas 79601, USA ⟨srosscoe@hsutx.edu⟩ 3Fossil Finder, Olhausen Estate, Abilene, Texas 79606, USA ⟨brianbethel72@gmail.com⟩


Abstract.—The Texas red beds represent one of the richest series of early Permian deposits in the world. In parti- cular, the Clear Fork Group has produced a diverse assemblage of temnospondyls, early reptiles, and synapsids. However, most of this material has been sourced from the oldest member, the Arroyo Formation, and the under- standing of the paleoecosystem of the younger Vale and Choza formations is less well resolved. Here we present a previously undescribed Vale locality, the first vertebrate-bearing locality from the formation to be described in detail in several decades, from near Abilene, Texas with juvenile diplocaulids, captorhinids, abundant material of rare taxa such as Varanops and diadectids, and the first report of a recumbirostran ‘microsaur’ from the formation. This assem- blage is atypical of early Permian deposits in the taxonomic and size distribution of the vertebrate fauna in compar- ison to other localities from the Vale Formation that preserve a greater abundance of aquatic taxa (e.g., fishes, Trimerorhachis) and synapsids (e.g., Dimetrodon). Minimal abrasion of the elements, relative articulation and asso- ciation of the specimen of Varanops, and the paucity of aquatic taxa suggest an ephemeral pond deposit in which organisms were preserved essentially in situ. Our characterization of the locality also permits a revision and discus- sion of the vertebrate faunal assemblage of the Vale Formation.


Introduction


Studies of the early Permian fauna, flora, and geology of Texas date to the origins of vertebrate paleontology in North America. Some of the earliest discoveries were made in the mid- nineteenth century by B.F. Shumard, the state geologist (e.g., Shumard, 1858, 1859). Extensive collection and study of the vertebrate fauna was primarily undertaken in the late nineteenth century and into the twentieth century by classic paleontologists such as Cope, Williston, Case, and Olson and resulted in a sig- nificant expansion of the knowledge of the early Permian land- scape with the discovery of many of the iconic taxa that typify the time period, such as Eryops Cope, 1877b, Diplocaulus Cope, 1877a, Trimerorhachis Cope, 1878, and Dimetrodon Cope, 1878 (Cope, 1877b, 1878). Even with exploration expanding into the southwest (e.g., New Mexico) and other areas of the midcontinent of North America (e.g., Oklahoma) from the mid-twentieth century to the present day, the described vertebrate fauna from Texas remains among the best character- ized and the most diverse of early Permian assemblages. Many vertebrate taxa are known from the Clear Fork Group (Leo- nardian) of Texas, which has traditionally comprised three for- mations (from oldest to youngest): the Arroyo, the Vale, and the Choza (e.g., Lucas, 2006; Nelson et al., 2013, but see Hentz, 1988 for a different model). Of these, the Arroyo Formation was the first to produce vertebrate material (dating back to work in the nineteenth century by Cope) and has been extensively


explored and studied, resulting in the most diverse vertebrate assemblage of the three formations (e.g., Olson, 1989, table 1). By contrast, material from the Vale and Choza formations was not reported until the mid-twentieth century (Olson, 1948, 1951c). Although these vertebrate assemblages contain sig- nificant overlap with the Arroyo assemblage at higher taxo- nomic levels, the documented taxonomic diversity is notably reduced. Four relatively fossiliferous localities within the Vale For-


mation of Texas have been previously described (Table 1). The geology and faunal assemblage of the Vale Formation was first described in detail by Olson (1948) based on a locality near Vera (Knox County), often referred to as the ‘northern Vale’ by the author, and was later expanded on in a number of separate articles that included fauna of the Choza Formation (Olson, 1951b, c, 1952a, b, 1954a−c, 1955, 1956a−c, 1958). Although Olson (1948, p. 186) indicated that workers had been previously unable to recover vertebrate material from post-Arroyo sedi- ments of the Clear Fork Group, this was in error. The earliest reported collection of significant vertebrate material from the Vale Formation was from 1939− 1940 on the land of C.O. Patterson near Lawn (Taylor County) under the direction of a Works Projects Administration (WPA) excavation led by the University of Texas, Austin; this material was first noted in an abstract by Wilson (1948) but was not fully reported until 1953 by the same author, who limited the bulk of the description to a new paleoniscoid taxon, Lawnia Wilson, 1953. Wilson noted


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