Tongue Bite Apparatus of Osteoglossomorph Fishes: Variation of a Character Complex

Abstract

Osteoglossomorpha were first defined on the basis of two characters: (1) the parasphenoid-tongue bite apparatus (TBA); and (2) the presence of processes associated with the second hypobranchial and/or basibranchial element of the ventral gill arches. These two characters have continued to be cited as unambiguous support of the monophyly of this group of basal teleostean fishes. The TBA has been vaguely defined as a ‘‘bite’’ of gill arch dentition against that of the parasphenoid and palatoquadrate bones. Historical definitions include both plesiomorphic (e.g., enlarged teeth on palatoquadrate bones and gill arches) and apomorphic (e.g., enlarged teeth on the parasphenoid and a direct connection between the sternohyoideus muscle and the ventral gill arch skeleton) character states. Also, the processes associated with the second gill arches are likely components of the osteoglossomorph TBA by providing an additional attachment surface for the sternohyoideus (i.e., in addition to the sternohyoideus-urohyal connection). There is variation both of presence and form of these processes within osteoglossomorphs. To use both the presence or absence of a TBA as well as its component characters in systematic analyses artificially weights the value of this character complex. This character complex should not be used in place of, and especially not in addition to, its component characters.