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

Abstract

New cranial material of the ‘rhynchodipterid’ lungfishSoederberghia groenlandicafrom 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 ofSoederberghiaare reconsidered in the light of new fossil specimens. Some of the difficulties in assessing the homologies between cheek bones inSoederberghiaand those of other lungfishes stem from confusion over the arrangement inRhynchodipterus, and a revised interpretation of this genus is proposed. The single infraorbital bar found inSoederberghiaprobably originates, in part, from an expanded bone 10 (quadratojugal) of the kind found inGriphognathus. 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 ofGriphognathus.G. minutidensis the sister taxon to this apical group, whileG. sculptaandG. whiteiare more remote from it.

A review of recent discoveries of exceptionally preserved fossil fishes from the Gogo sites (Late Devonian, Western Australia)

“…Challands (2015) revised the phylogeny of early lungfishes and his work supports earlier suggestion that the Gogo Chirodipterus is not congeneric with the type material from Germany, or with the Chinese species (Friedman 2007a). This work supports the suggestion that Griphognathus whitei from Gogo could be the plesiomorphic sister taxon to all other rhynchodipterids as first suggested by Friedman (2007b) and Long (2010). A description of the ontogenetic stages of the posterior neurocranium formation in the rhynchodipterid Griphognathus whitei has also been published (Campbell et al 2012).…”

The First Virtual Cranial Endocast of a Lungfish (Sarcopterygii: Dipnoi)

“…This contrasts with Youngolepis , Powichthys and porolepiforms -considered in the next section- which are assigned to the most basal part of the dipnoan stem group in the majority of recent analyses [28] , [55] but are not so obviously lungfish-like. The ‘fossil lungfish’ are all undisputed members of the stem group [22] , [55] , [56] and are always recovered crownward to Youngolepis , Powichthys and porolepiforms.…”

An Exceptionally Preserved Transitional Lungfish from the Lower Permian of Nebraska, USA, and the Origin of Modern Lungfishes

“…A similar interpretation has been made of the occiput of Soederberghia simpsoni [46] , and has been used to unite Soederberghia and Rhynchodipterus , and to generally support the monophyly of a rhynchodipterid clade. Friedman [47] has challenged this interpretation of Rhynchodipterus , however, pointing out that the described ribs in S. simpsoni resemble the two pairs of thickened anterior thoracic ribs found in Griphognathus and may not articulate with the cranium at all. We suggest a third alternative: the thickened anterior thoracic ribs may be homologous with the cranial ribs, and serve as the origin of portions of the M. rectus cervicus as well, and that articulation of these ribs with the occiput, or lack thereof, may reflect the fusion of post-occipital centra with the braincase.…”

“…The conical dentition of dipnoan outgroups is also replaced by a variety of derived palatal tooth arcades, generally involving a combination of denticles as well as extensive extradenteonal dentine [5] . In some taxa, this dentition forms a robust crushing surface, although in other taxa, the distribution of palatal denticles has been inferred to serve as a rasp [47] . The skull of most Devonian lungfishes would have been capable of exerting and resisting large bite forces, likely from crushing marine invertebrates with mineralized exoskeletons, but at the expense of gape and buccal suction.…”