The cranial endocast ofDipnorhynchus sussmilchi(Sarcopterygii: Dipnoi) and the interrelationships of stem-group lungfishes

Abstract

The first virtual cranial endocast of a lungfish from the Early Devonian,Dipnorhynchus sussmilchi, is described.Dipnorhynchus,only the fourth Devonian lungfish for which a near complete cranial endocast is known, is a key taxon for clarifying primitive character states within the group. A ventrally-expanded telencephalic cavity is present in the endocast ofDipnorhynchusdemonstrating that this is the primitive state for “true” Dipnoi.Dipnorhynchusalso possesses a utricular recess differentiated from the sacculolagenar pouch like that seen in stratigraphically younger lungfish (Dipterus, Chirodipterus, Rhinodipterus), but absent from the dipnomorphYoungolepis. We do not find separate pineal and para-pineal canals in contrast to a reconstruction from previous authors. We conduct the first phylogenetic analysis of Dipnoi based purely on endocast characters, which supports a basal placement ofDipnorhynchuswithin the dipnoan stem group, in agreement with recent analyses. Our analysis demonstrates the value of endocast characters for inferring phylogenetic relationships.