Cranial structure in the Devonian lungfish Soederberghia groenlandica and its implications for the interrelationships of ‘rhynchodipterids’

Abstract

New cranial material of the ‘rhynchodipterid’ lungfish Soederberghia groenlandica from Upper Devonian (Famennian) strata in East Greenland is described. Previously unknown structures identified here include components of the hyoid arch (ceratohyal, hypohyal) and the lower jaw (prearticular, dentary). Earlier interpretations of the cheek and mandible of Soederberghia are reconsidered in the light of new fossil specimens. Some of the difficulties in assessing the homologies between cheek bones in Soederberghia and those of other lungfishes stem from confusion over the arrangement in Rhynchodipterus, and a revised interpretation of this genus is proposed. The single infraorbital bar found in Soederberghia probably originates, in part, from an expanded bone 10 (quadratojugal) of the kind found in Griphognathus. Hypotheses that posit ‘rhynchodipterid’ polyphyly seem unlikely in light of a set of derived cranial characters that define a coherent radiation of long-snouted, denticle-bearing lungfishes known from the Late Devonian. The hypothesis presented here places ‘rhynchodipterids’ as a paraphyletic grade with respect to fleurantiids. Rhynchodipterus, Soederberghia, and fleurantiids form a clade to the exclusion of the species of Griphognathus. G. minutidens is the sister taxon to this apical group, while G. sculpta and G. whitei are more remote from it.