THE PECTORAL ANATOMY OF PANTODON BUCHHOLZI PETERS (A FRESHWATER FLYING FISH) AND THE RELATED OSTEOGLOSSIDAE

Abstract

Pantodon buchholzi, a small west African osteoglossid, is thought to be a freshwater flying fish. Its expanded pectoral fins and its body‐form would add credence to this supposition, whilst its pectoral musculature suggests the way in which flight could be effected.Anatomical studies on the pectoral girdle and musculature show that both are remarkably developed and are probably unique amongst the teleosts. The girdle is characterized by the hypertrophy of its mesocoracoid and correlated hyperdevelopment of certain abductor and adductor muscles. Unlike the deep abductor muscles of other fishes, those of Pantodon originate on the mesial aspect of the girdle and pass to the exterior through an enlarged coracoid foramen. The large blocks of deep abductors fill the girdle and even surround part of the pericardium. The superficial abductors are also hypertrophied and even project posteriorly away from the body‐line. The articulation of the pectoral fins is unusual since it does not allow the fins to be folded back against the body; the only fin movement possible is in the vertical plane.Apparently the pectoral musculature is highly adapted to spread and keep open the pectoral fine, at the samo time imparting a powerful dorso‐ventral motion to the fins. To this extent, Pantodon seems capable of true, flapping flight.In both its pectoral osteology and myology, and in body‐form, Pantodon differs markedly from other flying fishes. The latter, although belonging to numerous and phyletically distinct groups, all show convergent adaptations for flight.The pectoral anatomy of the related Osteoglossidæ (Heterotis niloticus and Osteoglossum bicirrhosum) is described. That of Heterotis does not differ greatly from the generalized isospondylid type, but the anatomy of Osteoglossum is intermediate between the Heterotis condition and that of Pantodon. Many characteristics of the Pantodon girdle and myology are clearly foreshadowed in Osteoglossum.The taxonomic status of P. buchholzi has long been uncertain, but the details of its pectoral anatomy and syncranial osteology clearly confirm its place in the Osteoglossidæ and suggest a relatively close relationship with Osteoglossum and Scleropages.