Taxonomic revisions of some Upper Cambrian and Lower Ordovician conodonts with comments on their evolution

The generic classification of Upper Cambrian and lowermost Ordovician conodonts has been revised in accord with multielement taxonomic concepts. Several species are reassigned from form taxonomy to new genera based on multielement apparatuses. New genera include Albicomis, Eocoriodotitus, Moriocostotius, Nogamiconus, Teridontus, and Utahcons. Muellerodus, n. gen., is proposed to replace Muellerina Szaniawski, 1971, which is a junior homonym of Muellerina Bassiouni, 1965, an ostracode. Taxonomy of Cordylodus Pander and various species assigned to it is extensively emended, and the genus is interpreted to possess a two-element apparatus. Setniacontiodus Miller is emended to include two-element apparatuses. Proconodontus Miller is emended and interpreted as having a one-element apparatus. New species described are Albicottus postcostatus, Cordylodus drucei, Proconodontus posterocostatus, P. tenuiserratus, and Utaliconus tennis. The holotype of Nericodus capillamentum Lindström is figured and interpreted as being broken. Lectotypes are designated for Fryxellodontus inornatus and F. lineatus, the genus being restricted to these two species.
Two distinct lineages of euconodonts can be recognized in upper Franconian strata. A Proconodontus lineage diversified in the Trempealeauan and developed several related two-element apparatuses (e.g., Eoconotiontus, Cambrooistodus, Cordylodus). Cambrooistodus did not survive into the Ordovician, a time when Cordylodus underwent much diversification. A Teridontus Tlineage was endemic to
Australasia during the Late Cambrian and evolved little. Following the latest Cambrian extinction within the Proconotiontits lineage, the Teridontus lineage rapidly produced additional genera with a variety of one-element apparatuses (e.g., Hirsutodontus, Clavoliamulus, Monocostodus) and two-element apparatuses (e.g., Serniacontiodus, Utahconus). General evolutionary trends include differentiation of
the posterior edge of elements (development of keels, costae, and adenticulate and denticulate processes), shortening of basal cavities, development of white matter, and thickening of walls with reduction of basal cones.