UPPER TRIASSIC INVERTEBRATES FROM THE ANTIMONIO FORMATION, SONORA, MEXICO

A diverse Upper Triassic tropical marine fauna from northwestern Sonora, Mexico, includes 31 taxa of tropical invertebrates including scleractinian corals, spongiomorphs, disjectoporoids, ''hydrozoans,'' thalamid and nonthalamid sponges, spiriferid and terebratulid brachiopods, gastropods, bivalves, coleoids, and anomuran microcoprolites. They occur within the late Karnian to Norian part of the Antimonio Formation (Antimonio terrane), which is juxtaposed against a fragmented portion of the North American craton. Most of the fauna is also known from the Tethys 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. Some taxa occur in displaced terranes of North America, especially in west-central Nevada (Luning Formation). A weak link exists with the California Eastern Klamath terrane but stronger ties exist with Peru. Among Sonoran sponges, Nevadathalamia polystoma was previously recognized only from the Luning Formation, western Nevada. Sponges Cinnabaria expansa, Nevadathalamia cylindrica, and a coral, Astraeomorpha sonorensis n. sp., are also known from Nevada. The corals Distichomeandra austriaca, Chondrocoenia waltheri, Pamiroseris rectilamellosa, and Alpinophyllia flexuosa co-occur in central Europe. Two new taxa, a spongiomorph hydrozoan, Stromaloporidium lamellatum n. sp., and a disjectoporoid, Pamiropora sonorensis n. sp., have distinct affinities with the Tethys. The geographically widespread North American brachiopod, Spondylospira lewesensis, and Pseudorhaetina antimoniensis n. gen. and sp. are among the Sonoran fauna. The Sonoran coleoid (aulacocerid) Dictyoconites (Dictyoconites) cf. D. reticulatum occurs in the Tethys realm and Calliconites cf. C drakei is comparable with a species from the Eastern Klamath terrane. Calliconites milleri n. sp. is the first occurrence of the genus outside Sicily. The bivalves Myophorigonia jaworskii, M. salasi, and Palaeocardita peruviana are known from Sonora and Peru. Eight gastropod taxa include Guidonia cf G. intermedia and G. cf. G. parvula, both previously known from Peru, and Eucycloscala subbisertus from the western Tethys. The pstropods are unlike those already known from other North American terranes.