. Bulletin of the British Museum (Natural History). Zoology . EVOLUTION OF A CICHLID SPECIES FLOCK 71 The monotypic genus Macropleurodus hicolor is, on the basis of its syncranial architecture, a member of the same species group. The jaw teeth of M. hicolor (Text-fig. 75) differ from those of other species in being coarser, more strongly in- curved and in generally retaining traces of a minor cusp (Text-fig. 75B). This cusp persists as a slight, vertical hump on the near-horizontal occlusal surface presented by the major cusp. The dentigerous arms of the premaxillae are bowed (usu
. Bulletin of the British Museum (Natural History). Zoology . EVOLUTION OF A CICHLID SPECIES FLOCK 71 The monotypic genus Macropleurodus hicolor is, on the basis of its syncranial architecture, a member of the same species group. The jaw teeth of M. hicolor (Text-fig. 75) differ from those of other species in being coarser, more strongly in- curved and in generally retaining traces of a minor cusp (Text-fig. 75B). This cusp persists as a slight, vertical hump on the near-horizontal occlusal surface presented by the major cusp. The dentigerous arms of the premaxillae are bowed (usually more so on one side than the other) ; consequently one side of the mouth is slightly. Fig. 41. Jaw tooth shape and pattern in two species of mollusc-eating Haplochromis, both oral shellers. A : H. prodromus, occlusal view, premaxilla uppermost. B and C : H. xenognathus, occlusal view of both jaws, and lateral view of lower jaw respectively. open even when the jaws are closed. This peculiar arrangement could be of adaptive significance in a species whose feeding involves grasping a snail so that it cannot withdraw into its shell. In other words, because of its arched upper border the gape is increased without an increase in the extent to which the dentary would otherwise have to be lowered. The near vertical ethmoid region (over which the ascending processes of the pre- maxillae run) in all H. sauvagei-growp species (see Text-figs 40 and 66) produces an. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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