A lungfish survivor of the end-Devonian extinction and an Early Carboniferous dipnoan radiation

Abstract

Until recently the immediate aftermath of the Hangenberg event of the Famennian Stage (Upper Devonian) was considered to have decimated sarcopterygian groups, including lungfish, with only two taxa, Occludus romeri and Sagenodus spp., being unequivocally recorded from rocks of Tournaisian age (Mississippian, Early Carboniferous). Recent discoveries of numerous morphologically diverse lungfish tooth plates from southern Scotland and northern England indicate that at least ten dipnoan taxa existed during the earliest Carboniferous. Of these taxa, only two, Xylognathus and Ballgadus, preserve cranial and post-cranial skeletal elements that are yet to be described. Here we present a description of the skull of a new genus and species of lungfish, Limanichthys fraseri gen. et sp. nov. that hails from the very earliest Tournaisian in the Ballagan Formation of Burnmouth, southern Scotland. The new specimen represents the earliest definitive Tournaisian lungfish skull material thus providing an invaluable insight into the response of this group, and indeed, the Sarcopterygii as a whole, immediately following the latest Devonian Hangenberg event. Phylogenetic analysis places Limanichthys fraseri within the Devonian 'phaneropleurid-fleurantiid' grade of lungfish and that the Carboniferous lungfish represent forms that have their origins deep in the Mid and Late Devonian as well as those from a unique Carboniferous radiation.

Systematics and description of the lungfish genusSagenodusfrom the Carboniferous of the UK

“…The KX-bone bears a prominent notch laterally, continuous with the margin of the Y-bone, where it bears the operculum. A similar feature is seen in Limanichthys, where it occurs on the separate X-bone (Challands et al 2019). Anterior to the E-, N-, and P-bones is a series of small elongate bones, which do not conform to a conserved pattern.…”

“…A similar feature is seen in Limanichthys , where it occurs on the separate X-bone (Challands et al . 2019). Anterior to the E-, N-, and P-bones is a series of small elongate bones, which do not conform to a conserved pattern.…”

“…There is little to distinguish the operculum of Sagenodus from that of Ctenodus (Sharp & Clack 2013) and the basal Carboniferous genus Limanichthys (Challands et al . 2019). The bone is large and robust; it is outwardly convex and its posterior margin forms a regular curve.…”

High lineage survivorship across the end-Devonian Mass Extinction suggested by a remarkable new Late Devonian actinopterygian

“…This taxon prompts a reconsideration of trait evolution and tree topology that together provide evidence that numerous lineages of ray-finned fishes radiated before and later survived the end-Devonian mass extinction. This revised perspective on ray-finned fish evolution complements emerging pictures of cryptic diversification before, and potentially high survivorship during, ecological crises at the end of the Devonian (30)(31)(32)(33)(34)(35).…”

Traquair's lungfish from Loanhead: dipnoan diversity and tooth plate growth in the late Mississippian

“…Eight species have so far been identified, with others awaiting description (Challands et al . 2015, in press). It has the same size range of fish and a similar variety of tooth plated-forms.…”