Jackson’s chameleon, Jackson’s horned chameleon, three-horned chameleon, or Kikuyu three-horned chameleon (Trioceros jacksonii) is a species of chameleon (family Chamaeleonidae) native to East Africa, but also introduced to Hawaii, Florida, and California.
Jackson’s chameleons 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 females generally have no horns, or instead have traces of the rostral horn (in the subspecies T. j. jacksonii and T. j. merumontanus). The coloring is usually bright green, with some individual animals having traces of blue and yellow, but like all chameleons, they change color quickly depending on mood, health, and temperature.
This is a small to medium-sized chameleon. Adult males reach a total length (including tail) of up to 38 cm (15 in) and females up to 25 cm (10 in), but more typical lengths are 15 to 25 cm (6 to 10 in). It has a saw-tooth shaped dorsal ridge and no gular crest. It attains sexual maturity after five months. The lifespan is variable, with males generally living longer than females.
The largest subspecies of Jackson’s chameleon is T. j. xantholophus, which has been captively bred since the 1980s.