Skeletal architecture, homologies and taphonomy of ozarkodinid conodonts

Conodonts are generally found as disarticulated skeletal elements, yet almost all aspects of conodont research rely on knowledge of the original arrangement of these elements in the apparatus. Analysis of rare, articulated 'natural assemblages' of taxa assigned to the order Ozarkodinida reveals that there was no significant variation in the skeletal architecture within this major group of extinct agnathans. The apparatus comprised 15 elements: a pair each of bilaterally opposed Pa and Pb elements; an anterior, axial Sa element flanked on each side by a group of four close-set, inward and forward inclined Sb and Sc elements; and above and outside each S group, an inward and forward pointing M element. We identify the S positions in the ozarkodinid apparatus as Sa, Sb1 Sb2, Sc1 and Sc2. Architectural analysis sheds new light on the taphonomy of conodonts, indicating that the majority of natural assemblages represent ozarkodinid carcasses that did not lie parallel to the sea floor. Our new apparatus model also goes some way to removing some of the more significant architectural barriers that havs hampered the recognition of homologies between conodont clades. There are many similarities between the apparatuses of ozarkodinids, prioniodinids, prioniodontids, and panderodontids; it is possible that the Conodonta was rather more conservative architecturally than current hypotheses suggest.