REVIEW AND REVISION OF LUDLOW (SILURIAN) TO LOCHKOVIAN (DEVONIAN) SPATHOGNATHODONTID CONODONT TAXA

Spathognathodontid conodonts were widespread in the late Silurian and early Devonian, yet this family is taxonomically poorly understood due to the conservative, carminate shape of its fossil elements. Several recent taxonomic revisions of the family have been undertaken, resulting in splitting of the genus Ozarkodina into six or more separate genera within the past decade. However, these taxonomic models often neglect significant conodont collections from the late Silurian and early Devonian of midcontinent North America.

A review of the literature and consideration of the new taxonomic models have allowed for a revised classification of Spathognathodontid conodont collections from the Hunton group of Oklahoma, the Bainbridge Formation of Missouri, the Decatur and Ross Formations of Tennessee, and the subsurface Frame Formation of west Texas. Two broadly defined groups of Spathognathodontid taxa have been identified: an older group consisting of Ozarkodina typica, Parazieglerodina auriformis, Genus S snajdri, Genus S crispa, and Wurmiella excavata; and a younger group that crosses the Silurian-Devonian boundary, consisting of Genus W eosteinhornensis, Lanea planilingua, Zieglerodina denticulata, Z. inordinata, Z. zellmeri, Z. cf. repetitor, and Z. cf. remscheidensis.

A good conodont indicator of the Silurian-Devonian boundary was not found in the collections studied here, but the generally clear distinction between the two faunal groups may be indicative of paleoclimatic changes or an oceanic ‘event’ similar to the mid-Ludlow Lau Event. Additionally, several of the taxa studied, particularly Parazieglerodina auriformis and Zieglerodina denticulata, may be useful individually for regional or global stratigraphic correlation.