Redescription of Sorbitorhynchus deleaskitus (Sarcopterygii, Dipnoi) from the Lower Devonian of China

Lungfishes first appeared in the Early Devonian and subsequently underwent a rapid radiation. They have persisted to the present day as iconic ‘living fossils’. Among Devonian lungfishes, the ‘chirodipterids’ or genus ‘ Chirodipterus ’ represent a polyphyletic group that is phylogenetically positioned between basal lungfishes and the more derived Late Devonian lungfishes. Here we present a redescription of the ‘chirodipterid’ lungfish Sorbitorhynchus deleaskitus from the Lower Devonian (Emsian) Dale Formation of Guangxi, China. New computed tomography data provide detailed anatomical information for the cranial endocast, skull, mandibular, gular, submandibular and postcranial skeleton. Sorbitorhynchus deleaskitus is characterized by an exceptionally large sacculolagenar chamber, as in Dipnorhynchus sussmilchi . The ventrally extended hypophyseal duct without a hypophyseal foramen represents an intermediate state of hypophyseal structure in early lungfishes. Additionally, S. deleaskitus has a distinct ventral expansion of the telencephalon, aligning with the gradual increase in this ventral expansion in Dipnoi. New data for S. deleaskitus contained in this study prompt a reassessment of the phylogenetic position of this species, which is recovered as the most crownward Early Devonian lungfish and placed as the sister taxon to ‘ Chirodipterus ’ australis . Finally, we discuss evolutionary trends in the submandibular series of Devonian lungfishes, documenting a clear pattern of reduction involving the loss of the median and posterior submandibulars.