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Fig. 2. Partial phylogeny of Clariidae based on the consensus tree of several
analyses on ribosomal DNA sequences presented elsewhere
(Jansen et al., 2006)
indicating the species studied (Clarias gariepinus, Gymnallabes typus
and Channallabes apus). Illustrations of the external head morphology
(left drawings) showing the closed skull roofs of C. gariepinus, Clarias
buthupogon and the outgroup sister species of Clariidae
Heteropneustes fossilis, as opposed to the hypertrophied jaw
adductors in G. typus and C. apus that fill a large part of
the head behind the eyes. This jaw adductor hypertrophy has evolved four times
independently in Clariidae, of which only two lineages are illustrated here.
The jaw adductors imposed on osteological drawings of the head (right
drawings) for the three species studied clearly illustrate the jaw muscle
hypertrophy in G. typus and C. apus compared to the
relatively slender jaw muscles of C. gariepinus, which are partly
covered by neurocranial bones. The graphs give the maximal bite force
(perpendicular to the lower jaw) at the anteriormost teeth (black bars) and
posteriormost teeth (grey bars) of animals with a cranial length scaled to 39
mm and at a gape angle of 10° as calculated by Herrel et al.
(Herrel et al., 2002).
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