By Heather Heying
This extremely speciose group of primarily arboreal lizards are represented by thirteen genera, and more than 650 species. They are widely distributed throughout South America, up into southern North America, and in the West Indies.
Anoles and their relatives are relatively small lizards (25 - 120 mm snout-vent length) with morphologies adapted for climbing. Together with the other seven families previously placed in Iguanidae (sensu lato), polychrotids have pleurodont teeth, which distinguishes them from other members of the Iguania (agamids and chamaeleons). Several synapomorphies diagnose the family, including endolymphatic sacs penetrating the nuchal musculature; and strongly bicapitate, bisulcate hemipenes. Additionally, polychrotids have extensive skull rugosity and midventrally confluent postxiphisternal inscriptional ribs, characters shared with some other iguanians. Furthermore, Anolis, the largest and most diverse reptile genus with close to 400 species, is diagnosed by a far posterior extension of the dentary, a reduced angular, the presence of subdigital lamellae bearing setae (toe pads similar to but less developed than that of gekkos), and reticular lingual papillae, among other characters.
Polychrotids are a diverse group of lizards. All are oviparous, and most are arboreal. (Polychrus even has a prehensile, nonautotomic tail). The terrestrial and rock-dwelling genera Pristidactylus and Phenacosaurus are the exceptions. Some polychrotids emit squealing vocalizations when stressed. Many members of the vast genus Anolis are well studied, especially in the West Indies. Several species of Anolis are known to segregate according to perch height (e.g. A. cuvieri in the crowns of trees, A. evermanni on trunks, A. pulchellus on bushes and in grass, and A. cooki on the ground.) Male Anolis have brightly colored dewlaps (subgular, extensible flaps of skin), which they use in defensive and courtship displays. Anolis advertisement displays -- dewlap extension in concert with head-bobbing -- have been better studied than those of any other lizards, and several studies have shown that females prefer the displays of males of their own species to those of others (with different colored dewlaps, or rate of head-bobbing). Anolis are further distinguished by laying a single egg at a time (alternating ovulation between left and right ovaries), though several clutches may be laid in a year. Anoles are very popular in the pet trade.
Polychrotids are unambiguously placed in the Iguania, a group that is sister to all other squamates (lizards and snakes). Within the Iguania, however, relationships are hotly contested. Until recently, almost 1,000 species, including those in Polychrotidae, were placed in Iguanidae (sensu lato), but Frost and Etheridge's (1989) analysis of iguanian systematics suggested eight monophyletic clades within that large family. They proposed new family status for these eight clades, including Polychrotidae (and a much reduced Iguanidae (sensu stricto). Most researchers (and Animal Diversity Web) follow this classification, although several formal criticisms have been made (e.g. Lazell 1992, Schwenk 1994, Macey et al 1997). Most researchers agree that the iguanian families that were not previously members of Iguanidae -- Agamidae and Chamaeleonidae -- form the monophyletic group Acrodonta, which is sister to the remaining families (equivalent to Iguanidae sensu lato, of which Polychrotidae is a member). Among the eight families of Iguanidae sensu lato, relationships are not resolved. Within Polychrotidae, at least one monophyletic group is apparent (the anoles, which includes Chamaeolis, Chamaelionorops, Anolis and Phenacosaurus). Monophyly of the para-anoles (Urostrophus and Anisolepis) is in some doubt.
Fossils are difficult enough to place without pinpointing the particular lineage within iguanians from which they arose. Iguanid (sensu lato) fossils are known from the Eocene in North America. Additionally, one fossil from the Cretaceous, Pristiguana, may be an iguanid (sensu lato), or a teiid.
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Contributors
Heather Heying (author).
