Originally Posted by Motherlode Chameleon
The above conversation explain genetically how these similarities happen. However does not explain the geographic anomalies that most of these similar species happen along the strip of Africa where Madagascar (the worlds oldest island) broke off along time ago. The question then is why are there not species elsewhere in Africa that have got similar genetic showing phenotype similarities to Furcifer or other Madagascar genus's.
I can think of one (Calumma globifer and parsonii to Chamealeo gracilis and senegalensis who slightly share similarities) however that is nothing compared to the similarities seen in Central Eastern Africa.
Its just a matter of concentrations of diversity. By far the two highest region of chameleon diversity are in Madagascar and east Africa. When you have high levels of diversity, you are going to get a wider range of morphological variation. Along with this variation you are more likely to find examples of convergence. While Kinyongia is the only mainland African genus know to exhibit similar rostral protuberances to some of the Calumma and Furcifer, this too can be a genetic cause. Its possible that of the generic level radiations on mainland Africa, only Kinyongia has experienced the activation of an encoded gene sequence for such rostral protuberances, and therefore, more of its members have it than seen in other genera. It only takes one gene activation event for a broader trend to result.
Also, you do see regional morphological convergence on mainland Africa, however. Look at T. oweni and the other three-horned Trioceros species or T. balebicornutus compared to some of the Cameroon montane species. While these are within the same genus, they are quite distantly related. Trace also mentioned the similarity between come of the T. bitaeniatus complex and some of the Bradypodion grass morphs.