NEW DATA REINFORCE THE CONCLUSION THAT THE INTER-REALM BARRIER IN NORTH AMERICA WAS SELECTIVELY BREACHED BY THE STROMATOPOROID HABROSTROMA CENTROTUM DURING THE LOCHKOVIAN AGE (EARLY DEVONIAN)

During most of the Early and Middle Devonian, marine organisms in what is now North America were separated into two faunal realms, the Old World and Eastern Americas Realms, by a land barrier that consisted of the Canadian Shield and the Transcontinental Arch. Previously, we concluded that this barrier was breached, but not circumvented, during the Lochkovian Age (Early Devonian) by the stromatoporoid Habrostroma centrotum (Girty), based on that species' simultaneous presence in Virginia, New York, Maine (all Eastern Americas Realm), and Bathurst Island in arctic Canada (Old World Realm); however, at that time we had only one specimen from Bathurst Island that was adequately identified. Here we test our original assertion by including four additional specimens from Lochkovian-age olistostromes in the Pragian-age Stuart Bay Formation of Bathurst Island, and eight specimens from the Lochkovian portion of the Goose Fiord Formation of southern Ellesmere Island, also in the Canadian Arctic, and therefore in the Old World Realm.

Cluster, canonical, and discriminant analyses of 129 specimens of Habrostroma from all of the locations mentioned above indicate that there are three species of Habrostroma present, H. centrotum (Girty), H. consimile (Girty), and H. microporum (Girty). Wilkes' lambda is statistically significant for two functions that separate three groups at p<.001. Habrostroma microporum is restricted to only New York, H. consimile is found in New York and Virginia, but H. centrotum occurs in all five areas. Realms are defined by mutually exclusive assemblages of genera, so it is surprising to see a species existing in two realms at the same time. Our conclusion that H. centrotum was able to breach selectively the transcontinental barrier is strengthened by the inclusion of these new data.