The structure and evolution of Ordovician conodont apparatuses

Abstract

Multielement taxonomy was instituted for Ordovician conodonts over a decade ago, and probably a majority of the multielement genera have been defined or are well understood. The present systems of notation for elements within apparatuses are inadequate and cumbersome. A new notation scheme is proposed which applies a single‐letter code to the position in the apparatus occupied by certain element morphotypes. The taxonomic status of all known Ordovician conodont genera is reviewed (appendix) using the new notation, and a new scheme to classify conodont apparatuses is presented. Five main apparatus types (I‐V) and seventeen subtypes (IA‐IC, etc.) are defined. Within these groups, all known Ordovician conodont genera can be accommodated, and probably few new groups are required to include all other conodont genera. The apparatus types and subtypes are defined on the basis of symmetry, curvature, and number of the element types, with a clear distinction being made between the first and second transition series. Certain homologous relationships, both between and within many apparatus types, are noted. The evolution of the five major types, and the subtypes, is traced through the Ordovician. The pattern of evolution suggests that the types and subtypes recognized are probably natural biologic groupings, largely reflecting phylogenetic change.

Orientation and Anatomical Notation in Conodonts

“…Difficulties with anatomical notation.-Anatomical notation in conodonts takes on particular significance because of its importance in disentangling biologically-valid ''multielement taxonomy'' from the taxonomically illegal practice of erecting discrete component elements as taxa without regard for the fact that several different ''taxa'' came from a single individual. It is no coincidence that the advent and proliferation of multielement taxonomy in the 1960s and 1970s (e.g., Bergström and Sweet, 1966;Webers, 1966;Jeppsson, 1971;Klapper and Philip, 1971) was accompanied by the development of several schemes of anatomical notation designed to identify and communicate which elements comprised multielement taxa and, usually by inference, what was homologous with what (e.g., Klapper and Phillip, 1971;Jeppsson, 1971;Sweet and Schönlaub, 1975;Barnes et al, 1979; for a review see Sweet, 1981b). All of these schemes derived the criteria for the application of a notation, and in some cases the notation itself, from the morphology of the elements.…”

“…One of the principal difficulties with the current terminology is that morphology and topology cannot be disentangled; they are inextricably linked in the definitions of terms and in the process of their application. Our knowledge of apparatus architecture in different groups of conodonts has now reached the point where the ultimate objective of previous notational schemes (e.g., Barnes et al, 1979;Sweet, 1981b) can be realized: we are now able to propose a scheme in which notation is defined and can be applied on the basis of topology, independently of element morphology.…”

A critical look at the Treatise family‐group classification of Conodonta: an exercise in eclecticism

“…Finally, with regard to the dichotomy depicted in Fig. 1, it should be noted that (Treatise) Hibbardellacea was largely restricted to the Ordovician Midcontinent Province, whereas (Treatise) Prioniodontacea was largely restricted to the North Atlantic Faunal Province (Barnes & Ffihraeus 1975); this was also noted by Barnes et al (1979).…”

Description and correlation of Late Ordovician conodonts from the D. ornatus and P. pacificus graptolite zones, Road River Group, northern Yukon Territory

“…(sensu formo) in the text and are listed in the synonymies as discrete elements. Conodont element nomenclature is from Barnes et al (1979).…”