UPPER TRIASSIC INVERTEBRATES FROM THE ANTIMONIO FORMATION, SONORA, MEXICO

A diverse Upper Triassic tropical marine fauna from northwestern Sonor a, Mexico, includes 31 taxa of tropical invertebrates including sclera ctinian corals, spongiomorphs, disjectoporoids, ''hydrozoans,'' thalam id and nonthalamid sponges, spiriferid and terebratulid brachiopods, g astropods, bivalves, coleoids, and anomuran microcoprolites. They occu r within the late Karnian to Norian part of the Antimonio Formation (A ntimonio terrane), which is juxtaposed against a fragmented portion of the North American craton. Most of the fauna is also known from the T ethys region. Sixteen Sonoran taxa co-occur in the western Tethys and five have never been known outside this region. Four additional taxa ( one identified only at genus level) are geographically widespread. Som e taxa occur in displaced terranes of North America, especially in wes t-central Nevada (Luning Formation). A weak link exists with the Calif ornia Eastern Klamath terrane but stronger ties exist with Peru. Among Sonoran sponges, Nevadathalamia polystoma was previously recognized o nly from the Luning Formation, western Nevada. Sponges Cinnabaria expa nsa, Nevadathalamia cylindrica, and a coral, Astraeomorpha sonorensis n. sp., are also known from Nevada. The corals Distichomeandra austria ca, Chondrocoenia waltheri, Pamiroseris rectilamellosa, and Alpinophyl lia flexuosa co-occur in central Europe. Two new taxa, a spongiomorph hydrozoan, Stromaloporidium lamellatum n. sp., and a disjectoporoid, P amiropora sonorensis n. sp., have distinct affinities with the Tethys. The geographically widespread North American brachiopod, Spondylospir a lewesensis, and Pseudorhaetina antimoniensis n. gen. and sp. are amo ng the Sonoran fauna. The Sonoran coleoid (aulacocerid) Dictyoconites (Dictyoconites) cf. D. reticulatum occurs in the Tethys realm and Call iconites cf. C drakei is comparable with a species from the Eastern Kl amath terrane. Calliconites milleri n. sp. is the first occurrence of the genus outside Sicily. The bivalves Myophorigonia jaworskii, M. sal asi, and Palaeocardita peruviana are known from Sonora and Peru. Eight gastropod taxa include Guidonia cf G. intermedia and G. cf. G. parvul a, both previously known from Peru, and Eucycloscala subbisertus from the western Tethys. The pstropods are unlike those already known from other North American terranes.