DEVONIAN PANTHALASSA AND PHACOPID TRILOBITES

Reconstruction of the late Lower to early Middle Devonian paleogeography is attempted here, using an area cladogram derived from a cladistic analysis of a trilobite group, Viaphacops Maksimova, 1972 (Trilobita, Devonian). This group is exclusively of Lower to Middle Devonian, occurring in three marine provinces; Eastern North America, Kazakhstan, and the Andean region of Bolivia and Peru. As noted previously by some authors (e.g. Ormiston, 1972, Scotese and McKerrow, 1990), the position of Kazakhstan is problematical. The cladistic analysis of Viaphacops species indicates a closer relationship between the Eastern North America and Kazakhstan than either to the Andean region. This preliminary result agrees with the lithological data, and proximity of these regions, and especially the position of Kazakhstan must be reconsidered on the paleomap. The presence of Paciphacops Maximova 1972 of the early Lower Devonian in the above regions and in Eastern Australia and in Great Basins (Nevada) suggests active migration route within the Pacific paleogeographic region, or the Panthalassa, in most of the Lower Devonian, as has already suggested by Ormiston (1972).