The family Cichlidae constitutes a monophyletic group in the order Perciformes.
Monophyly of the cichlid family is indicated by the presence of at least nine
synapomorphic morphological characters. Since the distribution of cichlids
ranges from South and Central America and Mexico to tropical Africa, Madagascar,
southern India, and Sri Lanka the cichlid family must have arisen before the
separation of Africa, South America, and India by continental drift more than
100 million years (MY) ago. The morphology of cichlid species has been studied
for almost 100 years and various classification schemes have been proposed.
The cichlid taxa in the Great Lakes of East Africa (Lakes Victoria, Malawi, and
Tanganyika) are of special interest, having undergone recent explosive adaptive
radiations leading to hundreds of different species. Lake Tanganyika, which is
approximately 12 MY old, provides an ancient reservoir of polyphyletic taxa,
some of which gave rise to more recent groups in lakes Malawi and Victoria. A
comparatively large genetic divergence between species of the genus Tropheus
from Lake Tanganyika was found to be accompanied by small morphological changes.
However, high morphological plasticity was found within the single New World species
Cichlasoma managuense. In addition, although some cichlid species from
different lakes resemble each other morphologically, molecular data indicate that
this similarity is due to convergent evolution.