New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/56 Early Permian vertebrate assemblage and its biostratigraphic significance, Arroyo del Agua, Rio Arriba County, New Mexico Spencer G. Lucas, Susan K. Harris, Justin A. Spielmann, David S. Berman, Amy C. Henrici, Andrew B. Heckert, Kate E. Zeigler, and Larry F. Rinehart, 2005, pp. 288-296 in: Geology of the Chama Basin, Lucas, Spencer G.; Zeigler, Kate E.; Lueth, Virgil W.; Owen, Donald E.; [eds.], New Mexico Geological Society 56th Annual Fall Field Conference Guidebook, 456 p. This is one of many related papers that were included in the 2005 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. 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ZEIGLER, AND RINEHART EARLY PERMIAN VERTEBRATE ASSEMBLAGE AND ITS BIOSTRATIGRAPHIC SIGNIFICANCE, ARROYO DEL AGUA, RIO ARRIBA COUNTY, NEW MEXICO SPENCER G. LUCAS1, SUSAN K. HARRIS1, JUSTIN A. SPIELMANN1, DAVID S. BERMAN2, AMY C. HENRICI2, ANDREW B. HECKERT1, KATE E. ZEIGLER3, AND LARRY F. RINEHART1 1New Mexico Museum of Natural History and Science, 1801 Mountain Road N. W., Albuquerque, NM 87104 2Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, PA 15213 3Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 ABSTRACT.—Early Permian vertebrate fossils from the upper part of the El Cobre Canyon Formation of the Cutler Group in the area around Arroyo del Agua, Rio Arriba County, New Mexico, encompass an extensive assemblage of chondrichthyans, osteichthyans, temnospondyls, microsaurs, a seymouriamorph, diadectomorphs, a parareptile, captorhinomorphs, an araeosce- lid, and basal or pelycosaurian-grade synapsids. This long and extensively collected and studied vertebrate assemblage comes from a narrow stratigraphic interval about 50-60 m thick, and we treat it as a single biostratigraphic assemblage. The presence of Zatrachys, Bolosaurus and Chenoprosopus indicates correlation of this assemblage to the Bowie Group in Texas, and thus suggests an age for the upper El Cobre Canyon Formation of early Wolfcampian. INTRODUCTION Whereas this initial collection is seen as a key record of a Lower Permian vertebrate fauna, it produced little to no response from Early Permian vertebrate fossils from the vicinity of Arroyo either Marsh or Cope, who generated only one paper each based del Agua in the Chama Basin of northern New Mexico (Fig. 1) on Baldwin’s collections (Marsh, 1878; Cope, 1881). are among the longest known and most extensively documented The second phase of collecting in the region began with a field Early Permian vertebrates from North America. These vertebrate party from the University of Chicago headed by S. W. Willis- fossils are of biostratigraphic value, and their correlation provides ton in 1911. This party recollected Baldwin’s locality, currently a relatively precise age for part of the Cutler Group in northern called the Baldwin bonebed. They also followed the fossiliferous New Mexico. Here, we review the history of study, localities, and horizon of that bonebed to the southeast along Mesa Montosa composition of the Arroyo del Agua Early Permian vertebrate (called “Mesa Poleo” by them), and one of the party, P. C. Miller, fauna and place the localities into lithostratigraphic context. This discovered a new quarry, later named the Miller bonebed (Fig. allows us to discuss the biostratigraphic correlation of the Arroyo 2). The resulting fauna and the stratigraphy of the quarries from del Agua Early Permian vertebrates. which the fauna were collected resulted in several publications that characterized the Lower Permian vertebrate fauna of north- PREVIOUS STUDIES ern New Mexico (Case, 1907, 1910, 1911, 1915, 1916; Huene, 1911; Williston, 1911a, b, 1914a, b, 1915, 1916a, b, 1917, 1918; The Lower Permian vertebrate-fossil-bearing strata surround- Williston and Case, 1912, 1913a, b, c, d; Case and Williston, ing the village of Arroyo del Agua, in Rio Arriba County, north- 1913a, b, c; Mehl, 1913; Douthitt, 1917). central New Mexico, have been actively prospected and excavated for more than 125 years. The nine well-collected quarries in the region (Fig. 2) have yielded extensive Lower Permian vertebrate material, which is rivaled only by the vertebrate fossil record of the Lower Permian redbeds of Texas (Berman,1993). The Arroyo del Agua localities have been collected in three phases. The initial discovery and collection was made by David Baldwin from 1877 to 1881, followed by various university field parties intermittently collecting from 1911 to the early 1960s. From 1979 to the present, the Arroyo del Agua localities have been predominantly collected by the Carnegie Museum of Natural History and more recently by the New Mexico Museum of Natural History and Science in asso- ciation with the Carnegie Museum of Natural History. In 1877-1881, David Baldwin collected in the Arroyo del Agua region for five field seasons, initially working for O.C. Marsh and later for E. D. Cope. Subsequent researchers concluded that what is currently known as the Baldwin bonebed (Fig. 2) is where he collected the first Permian vertebrates discovered in New Mexico. FIGURE 1. Cutler Group outcrops in the Chama Basin, northern New This collection was sent to O.C. Marsh in 1877 (Langston, 1953). Mexico, showing location of the Arroyo del Agua area. EARLY PERMIAN VERTEBRATE ASSEMBLAGE AT ARROYO DEL AGUA 289 FIGURE 2. Locality map of the nine Lower Permian vertebrate fossil quarries in the vicinity of the village of Arroyo del Agua (modified from Langs- ton, 1953). The V and L prefixes of numbers indicate specimens assigned to the quarries by the Museum of Paleontology, University of California, Berkeley, and the New Mexico Museum of Natural History and Science, respectively. Field parties from the University of California at Berkeley The most recent phase of collecting in the Arroyo del Agua began collecting in the Arroyo del Agua region in 1928. These region was begun by joint field crews from the Carnegie Museum crews were led by C. L. Camp and V. L. VanderHoof, who each Natural History and the University of Toronto. In 1979-1980, discovered the quarries that bear their names (Fig. 2). Excavation both the Cardillo quarry near Loma Salazar and the Morfin bone- of these sites was continued in 1934 and 1935, and during these bed on the southwest flank of Mesa Montosa (Fig. 2) were dis- field seasons the Welles, Anderson and Quarry Butte quarries covered and partially excavated. This prompted Berman et al. (Fig. 2) were discovered. All of the Berkeley quarries are tightly (1985) to describe the Morfin bonebed and specifically record the clustered near the small butte that they named Loma Salazar (Fig. occurrence of the rare dissorophid temnospondyl Ecolsonia cut- 2). Four important additions to the Arroyo del Agua fossil ver- lerensis, known otherwise from the VanderHoof quarry. Collect- tebrate assemblage were based on specimens from the original ing continued until the mid-1980s, resulting in several additions Camp quarry collections. These included the basal or pelycosau- to the vertebrate fossil assemblage of the Arroyo del Agua area, rian-grade synapsids, hereafter simply referred to as pelycosaurs, including the diadectomorph Tseajaia cf. T. campi, the araeos- the eothyridid Oedaleops campi and varanopseid Aerosaurus celid Zarcasaurus tanyderus, the seymouriamorph Seymouria wellesi, the diadectomorph Limnosceloides brachycoles and the sanjuanensis and the microsaur Stegotretus agyrus (Berman and