Possible pathology in the snout and lower jaw of the Chinese Devonian lungfish, Sorbitorhynchus deleaskitus (Osteichthyes: Dipnoi)

ABSTRACT

The holotype and only known specimen of Sorbitorhynchus deleaskitus, a large Devonian lungfish from Guangxi, China, is abnormal in the structure of the snout and lower jaw. The tooth plates show marked asymmetry and do not occlude when the jaws are placed in normal articulation. There is a large hemispherical depression with sinus tracts in the bone between the lower tooth plates. Both snout and lower jaw are abnormal in shape and only traces remain of ossified sensory tubules within the bone of the snout and mandible. The lower jaw of S. deleaskitus may have included a dentigerous cyst that developed from a persistent juvenile symphyseal tooth and grew large enough to distort the symphysis and cause malocclusion between the tooth plates. The cyst may have become infected, forming an abscess with sinus tracts in the bone below, and hyperplastic or neoplastic cells from the cyst may have spread to destroy normal sensory structures in the snout and lower jaw. If this interpretation is correct, the unusual structures in the holotype of S. deleaskitus are unlikely to have any significance for taxonomic or phylogenetic analysis.