rioceros jacksonii (common names Jackson's Chameleon or Three-horned Chameleon) is an African
chameleon belonging to the chameleon family (Chamaeleonidae).
Its generic name (trioceros) is derived from the Greek τρί- (tri-) meaning "three" and κέρας (kéras) meaning "horns". This is in reference to the three horns found on the heads of males. Its specific name is a Latinized form of English explorer and ornithologist Frederick John Jackson's last name, who was serving as the first Governor of Kenya at the time. The English word chameleon (also chamaeleon) derives from Latin chamaeleō, a borrowing of the Ancient Greek χαμαιλέων (khamailéōn), a compound of χαμαί (khamaí) "on the ground" and λέων (léōn) "lion". The Greek word is a calque translating the Akkadian nēš qaqqari, "ground lion".
Jackson's Chameleons are native to the humid, cooler regions of Kenya and Tanzania, East Africa, found in great numbers at altitudes over 3,000 m. The subspecies merumontanus can only be found on Mount Meru and the Arusha Region of Tanzania. The subspecies xantholophus was introduced to Hawaii in the 1970s and has since established populations on all main islands. This population was the primary source of Jackson's Chameleons for the exotic pet trade. However, the exportation of these animals (and many others) from Hawaii for the pet trade has been made illegal to prevent opportunists from willfully establishing further feral animal populations in order to capture and sell them.
They are sometimes called Three-horned
Chameleons because males possess three brown horns: one on the nose (the rostral horn) and one above each superior orbital ridge above the eyes (preocular horns), somewhat reminiscent of the ceratopsid dinosaur genus Triceratops. The female generally have no horns, or traces of the rostral horn (in the subspecies jacksonii and merumontanus). The coloring is usually bright green, with some individual animals having traces of blue and yellow, but like all chameleons it changes color quickly depending on mood, health, and temperature.