The oral apparatus composition of the Early Carboniferous elictognathid conodont ‘Siphonodella’

Conodont P1elements of‘Siphonodella’are the most important guide fossils for theTournaisian and topmost Famennian. Hypotheses on the origin and evolution of theelictognathid (‘Siphonodella’) clade are based exclusively on the morphology of one pairof elements in the 15 element apparatus, because of difficulties with its reconstruction.An unusually rich sample taken from the Kowala Quarry in the Holy Cross Mountains,dominated by the core elictognathid species‘S.’cooperi, enables corroboration of theinterpretation by Sandberget al. (1978) and falsification of some more recent hypothe-ses. The elements P1and P2of‘S.’cooperishow a relatively narrow population variabil-ity and do not change morphologically in the course of their ontogeny. In contrast,elements S and M profoundly transformed their pattern of denticulation and generalshape during growth. Juveniles are relatively underived and rather easily homologizedwith elements of other polygnathid apparatuses, but adults are of bizarre morphologyunlike any other conodonts. Such a pattern of ontogenetic transformation makes itlikely that small P2elements of relatively generalized morphology and matureDinodus‐type S elements associated with P1elements of‘S.’praesulcatain a Kowala sampletaken from the topmost Famennian nodular limestone bed, belong together to the sameapparatus. No Devonian conodont apparatus is known that could be compared withthe highly derived‘Siphonodella’as its possible ancestor. Apparently, the elictognathidlineage immigrated to the Rheic Ocean realm from an unknown source near the end ofthe Devonian.