CONODONT APPARATUS RECONSTRUCTION AND BIOSTRATIGRAPHY FROM THE HART RIVER FORMATION, EARLY CARBONIFEROUS, YUKON TERRITORY

Samples collected from the Hart River Formation in the Yukon Territory yielded numerous, excellently preserved conodont elements, including abundant ramiform and fewer pectiniform elements. Unlike many discrete element sets, these samples contain morphology ratios similar to what is found on bedding plane assemblages. This, in tandem with the low number of species present, made it possible to reconstruct the apparatuses using statistical methods. Apparatus reconstructions have been made for the species Bispathodus stabilis, B. aculeatus aculeatus, Vogelgnathus campbelli, and V. gladiolus. All apparatuses are assumed to conform to the 15-element model typical of ozarkodinid conodonts. The bispathodid apparatuses are similar to those published by Purnell and Donoghue (1998), differing only slightly in the morphology of the P2 element, and in the case of Bispathodus stabilis, the M element. The bispathodid apparatuses of this study differ more markedly from the reconstructed apparatus for Bispathodus stabilis by Over (1992). The P2 elements in Over’s apparatus are shorter, have more discrete denticles, and a less enlarged cusp. The Vogelgnathus campbelli apparatus reconstruction of this study notably differs in the P2 element morphology from previous reconstructions. Here the P2 element is found to have an elongate morphology lacking an enlarged cusp, while vogelgnathids typically exhibit an abbreviated P2 morphology dominated by an enlarged cusp. The presence of Gnathodus texanus, Bispathodus stabilis, Vogelgnathus campbelli, and Vogelgnathus gladiolus, place the Hart River in the Gnathodus texanus to Gnathodus bilineatus conodont zones and indicate a middle Visean (Lower Carboniferous) age, but Bispathodus aculeatus aculeatus is normally Tournaisian. The differences in apparatus structure found in the Bispathodus and Vogelgnathus species, and biostratigraphic issues may point to homeomorphy or previously unrecognized phylogenetic lineages.