The fossil record is sparse, but the history of chameleons may be more than 60 million years old. Although chameleons are believed to have originated in Africa or Madagascar, the oldest known fossil, 26 million years old, is Chamaeleo caroli-quarti from western Bohemia. Based on the known fossil record, chameleons were distributed in Africa but also in parts of the world where they are not found today, such as China, Bavaria, and western Bohemia. Chameleons eventually disappeared from the latter three regions, perhaps as a consequence of changing climatic conditions that favored cooler temperatures and lower humidity.
New areas were inhabited as chameleons radiated to more hospitable climates and evolved into new forms. Mountains, forests, and savannas isolated some species, and their morphologic characteristics evolved to include rows of scales called crests that were high, wavy, or spiky on the back (dorsal crest), throat (gular crest), or belly (ventral crest). A number of chameleons developed one, two, three, four, or six bony horns of different shapes and sizes, flexible extensions on the snout, movable flaps of skin on the side of the head, and other differentiating characteristics, such as patterns, coloration, and body shape and size. All chameleons retained certain prominent features, however, that in combination distinguish them from all other lizards, including projectile tongues used to capture prey, large protruding eyes encased in an eyelid with a tiny aperture referred to as eye turrets, toes fused in bundles of two and three to form grasping pincers, and a prehensile tail.
The classification of this diverse group of lizards has undergone many revisions in genera, families, subfamilies, species, and subspecies throughout the nineteenth and twentieth centuries. The naturalist John E. Gray introduced 16 genera in 1865, and Franz Werner later reduced the number to three genera but also created three new families in 1902. The numbers of species discovered and described increased over the years, but some of them later were eliminated as synonyms of taxa already described and named by previous authors. Werner recognized 70 species in 1902 and raised the number to 88 by 1911; by 1981 Vincent A. Wager recognized 113. By 1986 the number of recognized species had risen to 128, according to Charles Klaver and Wolfgang Böhme, who revised the entire phylogeny of the family based on the morphologic features of the male sexual organs and the lung morphology, bone structure, and chromosome characteristics. While elements of this classification system are not finalized and may be subject to change, it has been accepted worldwide as best representing the relationships within the family Chamaeleonidae. At the last published revision of the system in 1997, Klaver and Böhme recognized no subfamilies, six genera, and two subgenera (Chamaeleo and Trioceros). Within these groupings they cited a total of 171 forms (species plus subspecies):
A few subspecies were elevated to full species after 1997, and several new species were discovered and described, primarily from Madagascar. By 2002 the total number of valid species and subspecies was 180, but this number is likely to change in the future.
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