Arizona's Jurassic Fossil Vertebrates and the Age Of
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Heckert, A.B., and Lucas, S.G., eds., 2005, Vertebrate Paleontology in Arizona. New Mexico Museum of Natural History and Science Bulletin No. 29. 95 ARIZONA’S JURASSIC FOSSIL VERTEBRATES AND THE AGE OF THE GLEN CANYON GROUP SPENCER G. LUCAS1, ANDREW B. HECKERT2 AND LAWRENCE H. TANNER3 1New Mexico Museum of Natural History & Science 1801 Mountain Road NW, Albuquerque, NM 87104-1375; 2Department of Geology, Appalachian State University, ASU Box 32067, Boone, NC 28608-2067; 3Department of Biology, Le Moyne College, 1419 Salt Springs Road, Syracuse, NY 13214 Abstract—Most fossil vertebrates of Jurassic age from Arizona are derived from the Glen Canyon Group on the southern Colorado Plateau in the northeastern part of the state. Glen Canyon Group strata of Jurassic age in Arizona that yield fossils include the upper Dinosaur Canyon and the Whitmore Point members of the Moenave Formation, the Kayenta Formation, and the Navajo Sandstone. All of these units yield both trace (principally dinosaur footprint) and body fossils of tetrapods. To date, only the Kayenta Formation fauna is particularly diverse (more than 10 taxa), and the Kayenta fauna is one of the best known Dawan (Early Jurassic: Sinemurian) tetrapod faunas in North America, and includes numerous type specimens, representing important records of tritylodonts, theropod dinosaurs, amphib- ians, turtles, and mammals. Non-Glen Canyon Group records of Jurassic vertebrates from northern Arizona are limited to scattered occurrences of footprints in the Middle-Upper Jurassic Summerville Formation and a single documented Apatosaurus vertebra from the Morrison Formation. The only Juras- sic vertebrates from southern Arizona are fragmentary tetrapods from the Gardner Canyon Formation in the Santa Rita Mountains and undescribed osteichthyans from Upper Jurassic marine strata in the Chiricahua Mountains. Keywords: Early Jurassic, Glen Canyon Group, vertebrate fossils, Kayenta Formation, Moenave For- mation, Navajo Sandstone INTRODUCTION GC The Jurassic vertebrate fossil record of Arizona derives pri- FC marily from strata of the Glen Canyon Group in the northeastern part of the state (Fig.1; Tables 1-2), so the primary focus of this paper is on their stratigraphic occurrence and age. Other records MW include: (1) a crocodylomorph and tritylodontid from the Gardner Canyon Formation in the Santa Rita Mountains near Tucson, but AE this has never been documented other than a brief mention in Te- gowski and McCord (1996); (2) a few tetrapod footprints (assigned to theropod dinosaurs and pterosaurs) from the Middle-Upper Jurassic Summerville Formation in northeastern Arizona (Stokes, 1957; Lockley et al., 1996; Lockley and Mickelson, 1997); (3) some undescribed osteichthyans from Upper Jurassic marine strata in the Chiricahua Mountains (Lawton and Olmstead, 1995); and (4) a single caudal vertebra of the diplodocid sauropod Apatosaurus from the Morrison Formation of northern Arizona described by Curtice (1999) and included in Foster’s (2003) analysis of Mor- rison Formation paleoecology. Hereafter, this review focuses on Arizona’s vertebrate fossil record of and the age of the Glen Canyon Group. HISTORY OF STUDY Fossils from the Glen Canyon Group in Arizona were first reported by Brown (1933) and deposited at the American Museum C of Natural History (AMNH) in New York. Later, Brady (1935, ������ 1936) and Camp (1936) reported records that appear to have been SR recovered as byproducts of Camp’s extensive collecting program in the Triassic of Arizona and New Mexico for the University of FIGURE 1. Map of Arizona showing distribution of Jurassic strata and California Museum of Paleontology (UCMP) at Berkeley. Shortly Jurassic vertebrate fossil localities. AE = Aedii Eechii Cliffs, C= Chiracahua Mountains, FC = Four Corners, GC = Glen Canyon, MW = Moenkopi after this, the AMNH returned to northern Arizona (e.g., Colbert Wash, SR = Santa Rita Mountains. and Mook, 1951), and the UCMP collected additional vertebrates, principally from the Kayenta Formation, both in the middle part indeed most of the Kayenta Formation fauna collected over this of the century (Welles, 1954, 1970, 1984) and later in the 1980s (e.g., time interval, were reposited at the Museum of Northern Arizona Curtis, 1989; Curtis and Padian, 1999). These latter fossils, and (MNA) in Flagstaff. In addition to the UCMP and MNA collectors, 96 TABLE 1. Vertebrate taxa from the Glen Canyon Group in TABLE 2. Vertebrate ichnogenera from the Glen Canyon Group Arizona in Arizona Moenave Fm (Dinosaur Canyon Mbr) Moenave Fm (Dinosaur Canyon Mbr) Protosuchus Eubrontes Lepidosauria indet. Tetrasauropus Megapnosaurus (=Syntarsus) Wingate Sandstone (Triassic interval) Moenave Fm (Whitmore Point Mbr) Brasilichnium Semionotidae indet. Tetrasauropus Reptilia indet. Grallator Kayenta Fm Kayenta Fm Chondrichthyes Eubrontes Hybodontidae indet. Grallator Osteichthyes Osteichthyes indet. Navajo Sandstone Amphibia Brasilichnium Prosalirus bitis Shubin and Jenkins Eubrontes Eocaecilia micropodia Jenkins and Walsh Tetrasauropus Anapsida Otozoum Kayentachelys aprix Gaffney et al. Anomoepus Diapsida Sphenodontidae indet. Eopneumatosuchus colberti Crompton and Smith scientifically described tracks from the Glen Canyon Group until Protosuchus (=Archaeeosuchus richardsoni Brown) the 1990s. During the 1990s, as part of the general renaissance in Kayentasuchus walkeri Clark and Sues dinosaur ichnology, numerous workers described and illustrated Rhamphinion jenkinsi Padian tracks and trackways from every formation-rank unit in the Glen Dilophosaurus wetherilli (Welles) Canyon Group (e.g., Irby, 1993a,b, 1995, 1996; Lockley and Hunt, Syntarsus kayentakatae Rowe 1995; Bulkley, 1996; Morales, 1996; Nations et al., 1996; Rainforth “Shake and Bake Coelophysid” and Lockley, 1996a,b; Lockley et al., 2004). It is important to note Massospondylus sp. that most of these tracks and tracksites are uncollected, so speci- Scelidosaurus mens are not reposited in museums. Indeed, most are on Native Scutellosaurus lawleri Colbert American (principally Navajo Nation) lands, so researchers must Synapsida obtain permission from the relevant authorities to study them. Kayentatherium wellesi Kermack LITHOSTRATIGRAPHY Dinneibitodon amarali Sues Oligokyphus Strata that overlie the Chinle Group in northeastern Arizona Dinnetherium nezorum Jenkins et al. have long been assigned to the Glen Canyon Group (Fig. 2) and Navajo Sandstone were typically thought to be of Late Triassic, Triassic-Jurassic or Early Jurassic age (e.g., Averitt et al., 1955; Harshbarger et al., 1957; Tritylodontidae indet. Pipiringos and O’Sullivan, 1978; Blakey, 1994; Peterson, 1994). Protosuchidae indet. These are the (in ascending order) Moenave, Wingate, Kayenta Segisaurus halli Camp and Navajo formations (Fig. 2). Recent study (e.g., Lucas et al., Ammosaurus 1997a,b; Lucas and Heckert, 2001; Tanner et al., 2002; Molina-Garza et al., 2003; Lockley et al., 2004) confirms two important points Complete binomen including auther = type specimen advocated by some early students of the Glen Canyon Group: (1) the Chinle and Glen Canyon Groups have an interfingering and transitional (not unconformable) contact; and (2) the lower part the Museum of Comparative Zoology (MCZ) at Harvard has also of the Glen Canyon Group is of latest Triassic age. Current data been active in the area, collecting much from the Kayenta Forma- thus indicate that the Triassic-Jurassic boundary is in a relatively tion in northeastern Arizona during the 1970s and 1980s. Indeed, conformable (“continuously” deposited) rock succession within the bulk of the body fossil records from the Kayenta Formation the Moenave and Wingate formations, not at an unconformity at are based on the Harvard collections (e.g., Sues, 1983, 1985a,b, the base of the Glen Canyon Group, as advocated by some workers 1986a,b,c). Most recently, specimens from a crocodilian local- (e.g., Pipiringos and O’Sullivan, 1978). Our work also confirms ity in the Navajo Sandstone discovered and collected by Gerry the proposal of Marzolf (1994) that the Rock Point, Moenave and Bryant during his master’s thesis work are now reposited at the Wingate formations together constitute a single, unconformity- New Mexico Museum of Natural History (NMMNH) (Rinehart bounded tectonosequence. et al., 2001). The Moenave Formation is generally about 100-m thick The bulk of the collecting records listed above are those of and consists primarily of fine-grained sandstone, siltstone and body fossils. The history of study of vertebrate trace fossils in the shale (Harshbarger et al., 1957; Wilson, 1967; Irby, 1996). The Di- Glen Canyon Group is even more straightforward—with the ex- nosaur Canyon Member, a succession of brightly colored, reddish ception of Brady (1960) and Baird (1980), no workers identified and orange to light brown fluvial and eolian sandstone and siltstone 97 lithostratigraphy tetrapod Navajo Sandstone (e.g., Harshbarger et al., 1957; Luttrell, 1996). biostratigraphy The Kayenta Formation is up to 300 m thick in northern Arizona (Blakey, 1994). Navajo The Navajo Sandstone is a very thick (up to 750 m in north- 400 Sandstone m ern Arizona: Blakey, 1994) quartzose sandstone unit famous for its spectacular, large scale eolian crossbeds. The lower part of the Kayenta formation is equivalent to, and indeed intertongues with, the Kayenta Formation assemblage fluvial deposits of the Kayenta Formation, whereas the upper part Springdale is almost entirely of eolian origin and represents the uppermost Member