BIOSTRATIGRAPHIC AND PALEOBIOGEOGRAPHIC SIGNIFICANCE OF RARE STROMATOPOROIDS FROM THE LOWER DEVONIAN (EMSIAN) OF NEVADA

Stromatoporoids are a very rare component of the fossil fauna of the middle-upper Emsian (upper Lower Devonian) of Nevada. Three specimens, representing three species, are discussed here, in terms of their biostratigraphic and paleobiogeographic value. In ascending stratigraphic order, the species are: (1) Stromatoporella perannulata from the Bartine Member of the McColley Canyon Formation; (2) Syringodictyon n. sp. from the Coils Creek Member of the McColley Canyon; and (3) Stictostroma moosense from the Sadler Ranch Formation. Outside Nevada, Stromatoporella perannulata occurs in Emsian-age strata of Ellesmere Island, arctic Canada, and Emsian- and/or Eifelian-age strata of Ontario, New York, Ohio, and Kentucky. Syringodictyon is confined to the Emsian of Ellesmere Island, and Emsian and/or Eifelian of Ontario and New York. Stictostroma moosenseis known from only the Emsian and/or Eifelian of Ontario.

The occurrence of these species in Nevada strata, determined to be Emsian in age by well constrained conodont biostratigrahy, increases claims that strata in New York, Ontario, and Michigan that are either Emsian or Eifelian are more likely the former.

In terms of paleobiogeography, Stromatoporella perannulata, Syringodictyon, and Stictostroma moosense occur in both the Old World Realm and the Eastern Americas Realm. These dual occurrences contrast with the distributions of other taxa (e.g., brachiopods; rugose corals), where genera, let alone species, rarely occur in both realms. The results reported here are in agreement with previous studies that show four Emsian species in common between the Canadian Arctic and southwestern Ontario, and a Lochkovian species in common between the Canadian Arctic and the Appalachian Basin of Virginia, New York, and Maine.