A NOVEL APPROACH TO AN OLD PROBLEM: GEOMETRIC MORPHOMETRIC ANALYSIS OF THE GNATHODUS PUNCTATUS SPECIES COMPLEX IN ITS TYPE AREA (PRE-WELDEN SHALE, OKLAHOMA, USA)

The conodont Gnathodus punctatus (Cooper, 1939) likely represents a species complex that occurs within Mississippian strata ranging from the G. punctatus Zone into the Polygnathus communis carina Zone (Kinderhookian- Osagean boundary and early Osagean). Clarifying the morphological variation present in G. punctatus and solidifying the species concept is important because it is the index taxon of the most commonly used conodont zone to correlate the K-O boundary across the North American stage type areas in Missouri and coeval Midcontinent strata. Previous studies have acknowledged large amounts of morphological variation within Gnathodus as a whole. Recently, Boardman et al. (2013) proposed fifteen possible new species including two new G. aff. punctatus, a primitive morphotype of G. punctatus, and an advanced morphotype of G. punctatus.

Typically, problems of species identity can be approached by comparison to the type specimen. In the case of G. punctatus, the type is a juvenile and the other figured specimen is heavily damaged. Cooper also named several congeners from the same horizon, but it is unclear whether they are separate species or if any of them correspond to Boardman’s species. To address these issues, this study will use landmark-based geometric morphometric analyses to quantify morphological variation within the total set of “G. punctatus” specimens (principal component analysis) as well as within and between predetermined groups (canonical variate analysis). The analyses identify sets of shape variation that characterize the spectrum of morphology and result in the separation in morphospace, if any, between specimens or groups. Specimens for these analyses will include the published type images of G. punctatus and Cooper’s other proposed species, as well as “punctatus-group” specimens from new collections at Cooper’s type locality and two nearby outcrops in Oklahoma. Results will help determine more consistent and reliable diagnostic features that should be used for identification of G. punctatus and possibly additional species. Future research will incorporate G. punctatus from other localities, such as the Osagean type area, for a broader morphometric understanding of the species complex as a whole, as well as more precise identification of the G. punctatus Biozone and K-O boundary.