This group of slender, long-limbed lizards was formerly, along with six other new families, considered a subfamily of Iguanidae (see Frost and Etheridge 1989). The corytophanids (previously known as the basiliscines) are represented by nine species, in three genera. They are limited in distribution to the northern reaches of tropical America, from central Mexico to northwestern South America.
The casquehead lizards are a better-supported clade than many among the iguanians. They are all thin, long-tailed lizards, with long limbs, and relatively small size (9-20 cm snout-vent length). In Corytophanes and Laemanctus, both sexes sport large head crests and casques; in the highly sexually-dimorphic Basiliscus, only the males have crests (and males grow faster than females after their first year of life. Together with the other seven families previously placed in Iguanidae, corytophanids have pleurodont teeth, which distinguishes them from other members of the Iguania (agamids and chamaeleons). Synapomorphies of the family include a y-shaped parietal roof with large median crest; parietal foramen in the frontal bone (not known in Laemanctus), and basiliscine-type caudal vertebrae. Several additional characters may diagnose the group, depending on its placement within Iguania.
Casquehead lizards range from rainforests to dry scrub forests. Corytophanes and Laemanctus, which together form a clade, are highly arboreal, living in the forest canopy. By contrast, Basiliscus tends to forage on the forest floor, often near water. The common name for lizards of the genus Basiliscus, jesus christ lizards, alludes to an escape behavior in which they run bipedally on the surface of water. This is made possible by the presence of enlarged, squarish, fringed scales on their toes, as well as highly muscularized legs. On some occasions, Basiliscus may even seek refuge underwater, dropping from arboreal perches into water, and hiding under rocks for short periods. The common basilisk, Basiliscus basiliscus, has a sail on its back, in addition to its head crest. Corytophanes uses its crest in a defensive display, orienting its head towards predators such that it appears larger than it actually is. Corytophanes is also a sit-and-wait predator, catching prey items once a day or less, but regularly eating items half as long as its own body. All corytophanids primarily eat insects and other small animals; and all are oviparous, except the ovoviviparous Corytophanes percarinata.
Corytophanids 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 Corytophanidae, 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 Corytophanidae (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 Corytophanidae is a member). Among the eight families of Iguanidae sensu lato, which includes Corytophanidae, relationships are not resolved.
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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Heather Heying (author).