Trioceros

{{Short description|Genus of lizards}}

{{automatic taxobox

| image = Jackson's Chameleon444.jpg

| image_caption = Jackson's chameleon
(Trioceros jacksonii)

| taxon = Trioceros

| authority = Swainson, 1839

| type_species = Chamaeleo oweni

| type_species_authority = Gray, 1831{{NRDB species |genus=Trioceros |species=oweni |access-date=17 May 2022}}

}}

Trioceros is a genus of lizards in the family Chamaeleonidae, the chameleons, native to lowlands and highlands in the African mainland, ranging from Ethiopia south to Mozambique and west as far as Ghana. Trioceros was considered a subgenus of the genus Chamaeleo until 2009, when it was elevated to full genus level.{{aut|Tilbury, C.R., & Tolley, K.A.}} (2009). "A re-appraisal of the systematics of the African genus Chamaeleo (Reptilia: Chamaeleonidae)". Zootaxa 2079: 57–68.

Trioceros vary greatly in appearance and size. Many species in the genus have various ornaments, such as one to four horns on the head, crests on the nape or throat, or spines or sail-like structures on the top of the back or tail. They are primarily found in adult males, but generally reduced or even absent in females, and there are also many species in the genus where both sexes lack conspicuous ornaments. Although horn-like structures are found in certain other chameleon genera, Trioceros is the only where it can be cylindrical, annulated and bony.

Trioceros contains species that lay eggs (similar to most other chameleon genera) and species that give birth to live young (similar to only Bradypodion). It is likely that giving birth to live young is an adaption to temperature, as it in Trioceros generally is found in species from highlands. The relatively cold highland climate slows the development of eggs laid in the ground; when instead retained inside the body until birth, a female can actively sun bask to increase the temperature.{{cite journal|last1=Hughes|first1=D.F.|last2=Blackburn|first2=D.G.|year=2020|title=Evolutionary origins of viviparity in Chamaeleonidae|journal=Journal of Zoological Systematics and Evolutionary Research|volume=58|issue=1|pages=284–302|doi=10.1111/jzs.12328|doi-access=free}}