Apparatus structure of the latest Silurian to Early Devonian conodont Icriodus woschmidti hesperius Klapper et Murphy, and some comments on phylogeny

The apparatus structure of the latest Silurian to Early Devonian conodont Icriodus woschmidti hesperius from sequences in north Queensland, Australia, consists of Pa, Pb and M elements with a symmetry transition series of distinct, but variable, coniform elements. A similar complex of cones was recovered from Ludlow (siluricus Zone) strata; although the apparatus structure is incomplete, the results indicate the existence of a likely ancestral form of the genus Icriodus. The cryptic origin of the genus is discussed in general terms. A distomodontid or icriodellid origin is considered possible. The former is supported by some morphological similarities of the symmetry transition series and stratigraphic considerations. The documentation of a Pa element with morphology apparently transitional between Icriodella and Icriodus supports the second possibility.