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The Arlington Archosaur Site (AAS) is located in the Dallas–Fort Worth Metroplex of North Texas, within the suburban city of Arlington, in Tarrant County (Fig. 5.1). It was discovered independently in 2003 by University of Texas, Arlington, students Phil Kirchhoff and Bill Walker, and local fossil collector Art Sahlstein. Among the first fossils found and reported were crocodyliform and ornithopod dinosaur remains, leading one of us (DJM) to propose the site’s name. Unfortunately, the landowner at the time of discovery refused to grant land access. From 2003 to 2007, the 2200 acres of fossil-rich land in northern Arlington was unavailable for paleontological exploration and scientific study. It was not until a new landowner, the Huffines family, purchased the land in 2007 that formal exploration and excavation began.

Amateur fossil hunters have collected scattered dinosaur remains in the Woodbine Formation for many years, but little of this material is described in the scientific literature. Isolated skeletal remains of theropods, nodosaurid ankylosaurs, and iguanodontian ornithopods are reported by Lee (1997a) from multiple localities in the greater Dallas–Fort Worth metroplex. A proximal left femur, complete tibia, and fibula are described from a locality in the Lewisville Member of the Woodbine Formation, and a humerus and teeth have been described from the overlying Arlington Member. All of this material is assigned to indeterminate hadrosaurids (Lee, 1997a). Ornithopod tracks from the Woodbine are described by Lee (1997b), and assigned to the ichnotaxon Caririchnium protohadrosaurichnos. The best known ornithopod from the Woodbine Formation, Protohadros byrdi, was discovered at Flower Mound in 1994, and was later named in honor of its discoverer, Dallas Paleontological Society member Gary Byrd (Head, 1998). Protohadros byrdi is based on a nearly complete skull and scant postcrania from the Arlington Member of the Woodbine Formation (Head, 1998), and whereas it was originally described as the basal-most member of Hadrosauridae, subsequent analyses have recovered it as a non-hadrosaurid hadrosauroid (Norman, 2002; Horner et al., 2004; Prieto-Márquez, 2010a).

Given the proximity of fossiliferous strata of the Woodbine Formation to a major and expanding metropolitan area, it is surprising that more significant fossil material has not been recovered from the unit. Such material would likely provide valuable insight into the turnover of taxa and the origin of major clades (e.g., hadrosaurids) that occurred during the middle Cretaceous, for which there is little fossil evidence from North America (Jacobs and Winkler, 1998).

This contribution describes the stratigraphy, depositional setting, taphonomy, and postcranial anatomy of a basal hadrosauroid from the Woodbine Formation, and thus, further elaborates the nature of the formation’s hadrosauroid fauna. The new ornithopod material consists of specimens UTA-AASO-2003 and UTA-AASO-125 (University of Texas, Arlington–Arlington Archosaur Site field numbers), now stored in the collections of the Perot Museum of Nature and Science, Dallas, Texas. (Field numbers provided by C. R. Noto, August 2013. At the time of publication all material described here has been received by the Perot Museum of Nature and Science, Dallas, Texas, where it will be accessioned and assigned specimen numbers [A. R. Fiorillo, pers. comm., August 2013]). All specimens described here were recovered from the AAS, intermittently, from 2003 to 2008. The adult material includes a femur; scapula; coracoid; ilium; ischium; pubis; ribs; an axis; and cervical, dorsal, and caudal vertebrae. Although an assemblage of hadrosauroid postcrania such as this is potentially important for assessing phylogenetic relationships (Brett-Surman, 1979; Davies, 1983; Maryànska and Osmólska, 1984; Casanovas et al., 1999; Prieto-Márquez et al., 2006; Brett-Surman and Wagner, 2007; Poole, 2008; McDonald et al., 2010; Campione, this volume) we are not yet able to determine whether the AAS ornithopod material represents a known taxon, such as Protohadros byrdi, or a new taxon. Such conclusions must await further discoveries and research.

5.1. Location of the Arlington Archosaur Site (AAS) on a Texas map, with outlines of counties in which Woodbine Formation exposures occur. The AAS study area is in the city of Arlington, in northeastern Tarrant County.

Institutional Abbreviations SMU, Shuler Museum of Paleontology, Southern Methodist University, Dallas, Texas; UTA-AASO, University of Texas, Arlington–Arlington Archosaur Site, Arlington, Texas.

Anatomical Abbreviations ac, acetabulum; ap, pseudoacromion process; C, coracoid; ccv, cranial convexity; cf, coracoid foramen; cp, capitulum; cr, coracoid ridge; crp, cranial pubic process; cs, coracoid suture; ctr, base of cranial trochanter; dia, diapophysis; dr, deltoid ridge; eb, expanded boot; fn, femoral neck; ftr, fourth trochanter; gl, glenoid; gtr, greater trochanter; haf, hemal arch facet; IL, ilium; IS, ischium; ilp, iliac peduncle; isp, ischial peduncle; obp, base of obturator process; od, odontoid process; P, pubis; pap, preacetabular process; par, parapophysis; pop, postacetabular process; poz, postzygapophysis; prz, prezygapophysis; pup, pubic peduncle; R, rib; S, scapula; sac, suprailiac crest; scl, scapula labrum; scs, scapula suture; svf, facets for sacral vertebrae; tb, tuberculum; V, vertebra; vl, ventral lip.