522 Harris et al., eds., 2006, The Triassic-Jurassic Terrestrial Transition. New Mexico Museum of Natural History and Science Bulletin 37. THE GEOGRAPHIC DISTRIBUTION AND BIOSTRATIGRAPHY OF LATE TRIASSIC-EARLY JURASSIC FRESHWATER FISH FAUNAS OF THE SOUTHWESTERN UNITED STATES ANDREW R. C. MILNER 1 , JAMES I. KIRKLAND 2 AND TYLOR A. BIRTHISEL 3 1 St. George Dinosaur Discovery Site at Johnson Farm, 2180 East Riverside Drive, St. George, UT 84790, E-mail: amilner@sgcity.org; 2 Utah Geological Survey, 1594 West North Temple, Suite 3110, P.O. Box 146100, Salt Lake City, UT 84114-6100, E-mail: jameskirkland@utah.gov; 3 University of Nevada Las Vegas, Department of Geology, 4505 Maryland Parkway, Box 454010, Las Vegas, NV 89154, E-mail: tbirthisel@hotmail.com Abstract—Results from a biostratigraphic and geographic overview of known freshwater fish species from the Upper Triassic Chinle and Dockum formations (Carnian to Rhaetian) and the Lower Jurassic Moenave and Kayenta formations (Hettangian to Pliensbachian?) in the southwestern United States are compared with known land-vertebrate faunachrons (LVF). Five fish-bearing intervals are recognized in the Upper Triassic of the Ameri- can Southwest, and an attempt to correlate these fish faunas with known LVFs is undertaken. Fishes from “Fish Fauna A” (upper Otischalkian, upper middle Carnian) and “Fish Fauna B” (lower Adamanian, upper middle Carnian) LVFs are represented mostly by isolated fossils from microvertebrate sites, although some fish sites containing articulated specimens are known; however more complete fish are recognized from the other biochrons. “Fish Fauna C” and “Fish Fauna D” are lower and upper Revueltian, respectively (or lower and middle Norian). Fish Faunas “B” and “C” have distinct fish taxa: “B” has Diplolonchidion murryi and Xenacanthus sp., and “C” has “Acrodus” sp., Gyrolepis sp., Australosomus sp., and Quayia zideki. “Fish Fauna D” includes fossils from many localities in the Owl Rock Member of the Chinle Formation that produce both complete fish and typical, disarticulated microfossils. Distinct taxa from “Fish Fauna D” include Turseodus dolorensis, Lasalichthys hillsi, Cionichthys greeni, a new species of redfieldiiform, and at least two new species of Semionotus. “Fish Fauna E” correlates with the upper Apachean LVF (upper Norian-Rhaetian) and occurs at localities in the Redonda Forma- tion that mostly produce complete fish fossils. It is very similar to “Fish Fauna D” but has lower diversity. The Lower Jurassic (Hettangian) “Lake Dixie Fish Fauna” has increased threefold in diversity since the discovery of abundant fossil fish at the St. George Dinosaur Discovery Site at Johnson Farm in southwestern Utah. Additional taxa include a variety of semionotids (some of which are new species), a new taxon of Chinlea-like coelacanth, a new hybodont shark, a new lungfish, and a new palaeonisciform. The youngest fish fauna is termed the “Kayenta Fish Fauna,” represented by a low diversity of known fish of Sinemurian to possible Pliensbachian age fish. INTRODUCTION Many of the Chinle Formation (Group of some authors) fish faunas have been well documented in the American Southwest (Schaeffer and Gregory, 1961; Schaeffer, 1967; Schaeffer and Mangus, 1970; Murry, 1986, 1987, 1989a, b; Elliott, 1987; Kirby, 1988, 1989a, b; Huber et al., 1993; Kaye and Padian, 1994; Hunt, 1997; Heckert and Lucas, 2002a, b; Murry and Kirby, 2002; Johnson et al., 2002; Heckert, 2004; Heckert and Jenkins, 2005; Milner et al., 2006). In contrast to these Late Triassic fish faunas, our knowledge of Early Jurassic fishes in the southwestern United States is very limited (Eastman, 1917; Hesse, 1935; Schaeffer and Dunkle, 1950; Kirkland, 1987, 1998; Curtis and Padian, 1999), unlike well known Early Jurassic fish faunas from the Newark Supergroup of eastern North America (Eastman, 1911, 1917; Schaeffer, 1941, 1948, 1952, 1984; Shainin, 1943; Schaeffer and Gregory, 1961; Schaeffer et al., 1975; Olsen et al., 1982; McCune et al., 1984; McCune, 1986, 1987a, b, 1989, 1990, 1996; McCune and Schaeffer, 1986; Olsen and McCune, 1991; Olsen and Rainforth, 2002). Recently, however, a greater under- standing of these fish is emerging due to extensive collections from the St. George Dinosaur Discovery Site at Johnson Farm (SGDS) in southwest- ern Utah that are only beginning to be prepared (Chin et al., 2003; Milner et al., 2005; Milner and Lockley, 2006; Milner and Kirkland, this vol- ume). The purpose of this paper is to review what is currently known about the fish faunas from the Upper Triassic and Lower Jurassic of the southwestern United States. Stratigraphic Nomenclature Confusion and controversy over the nomenclature of Upper Tri- assic formations in the southwestern United States, particularly dealing with the Chinle and Dockum, continues to this day. Some argue that the Dockum Group should be abandoned all together, and/or lowered to formation status and subsumed into the Chinle Group (Lucas, 2001; Lucas et al., 2001; Heckert, 2004; Lucas et al., 2005a). For this study, a biostratigraphic approach is used to link widely separated fish occur- rences into one unified system of correlation (Lucas and Hunt, 1993; Lucas, 1996, 1998; Lucas and Huber, 2003; Lucas et al., 2005b). For simplicity, in this paper we group fish from different formations (e.g., Chinle, Dockum, Popo Agie, etc.) into separate “fish faunas” based on correlation with known land-vertebrate faunachrons (LVF). However, we refer to the Chinle as a formation rather than a group, in accordance with Utah Geological Survey mapping conventions (G. Willis, personal commun., 2006). Institutional abbreviations used in this paper include: AMNH, American Museum of Natural History, New York, New York; DOL, Dan O’Laurie Museum, Moab, Utah; MCZ, Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts; UCMP, Uni- versity of California Museum of Paleontology, Berkeley, California; UMNH, Utah Museum of Natural History, University of Utah, Salt Lake City, Utah; SGDS, St. George Dinosaur Discovery Site at Johnson Farm, St. George, Utah. STRATIGRAPHY AND BIOCHRONOLOGY OF LATE TRIASSIC FISH FAUNAS IN THE SOUTHWEST U.S.A. The Upper Triassic rocks of the Chinle Formation, and age-equiva- lent geologic units, range in age from about 223-201 million years in age, spanning the mid-Carnian to mid-Rhaetian stages (Table 1). The Chinle