A new origin of the ‘modern’ lungfish dentition revealed by taxonomic overlap between Devonian and Carboniferous dipnoans

Lungfishes (Dipnoi, Sarcopterygii) initially radiated in the Early Devonian, and reached the apogee of their diversity during this period, especially with regard to their dentitions. Following the end-Devonian extinction, most of this diversity was lost and remained low throughout the Carboniferous and the rest of the Palaeozoic, mainly represented by the incredibly successful ‘Sagenodus-like’ dental morphology with sharp rows of fused teeth. Nevertheless, the exact scenario of lungfish evolution across the Devonian-Carboniferous boundary remains ambiguous. Recent work on new dipnoan assemblages from the Famennian (Upper Devonian) and Tournaisian (Lower Carboniferous) has challenged our understanding of lungfish evolution across this boundary. These studies suggest that the end-Devonian extinction did not impact lungfishes as strongly as other sarcopterygians, and that many Carboniferous lineages have origins that stretch much further back in time. However, concrete fossil evidence supporting these new hypotheses remained exceedingly rare. Here, we describe a highly derived lungfish tooth plate from the Famennian of the Tafilalt region in Morocco. This specimen’s morphology is akin to that of the Carboniferous genus Sagenodus, often dubbed as the earliest ‘modern’ lungfish. Although the material is not sufficient for a precise taxonomic identification or placement with phylogenetic analyses, it shows that a Carboniferous lineage—the Sagenodontidae—extends deep roots into the Devonian. This specimen supports recently developed ideas about lungfish evolution blurring across the Devonian-Carboniferous boundary and pushes back the origin of the ‘modern’ lungfish dental morphotype by some 20 million years from the Visean to the Famennian.