REVIEW AND REVISION OF LATE SILURIAN SPATHOGNATHODONTID CONODONT TAXA OF THE SOUTH-CENTRAL UNITED STATES

The Spathognathodontid family of conodonts produced several groups during the Late Silurian and Early Devonian with relatively conservative, carminate P1 elements. Because these forms tend to develop intergrading morphologies, they have resisted resolution into convenient, reliable taxonomic divisions. Study of collections from the south-central United States (Henryhouse and Haragan Formations, south-central Oklahoma; Frame Formation, west Texas; Bainbridge Formation, south-eastern Missouri; Decatur and Ross Formations, western Tennessee) has provided additional data to help both in the resolution of taxa and in the establishment of geographic and biostratigraphic ranges. At least four morphotypes of the complex remscheidensis/eosteinhornensis group have been identified, including the first recorded occurrence of “Ozarkodina” (New Genus W of Murphy et al.) eosteinhornensis in Oklahoma. P1 elements with incipient terraces on the basal cavity grade into forms that can possibly be assigned to “Ozarkodina” planilingua. Variation in P1 element denticle morphology within the remscheidensis/eosteinhornensis group ranges from fine, needle-like denticulation, through the majority of specimens with uniformly sized, triangular or palisade-like denticles, into specimens with extremely irregular denticulation that resemble, but differ from the P1 elements of the much younger species Zieglerodina remscheidensis. Other Spathognathodontids include Ozarkodina martinssoni auriformis in Ludfordian strata and the Oz. snajdri-crispa transition crossing the Ludlow-Pridoli boundary interval. Preliminary comparisons with collections and published descriptions from Europe, Australia, and elsewhere in North America suggest that the Silurian and Devonian Spathognathodontidae may have some unutilized potential for correlation worldwide.