This small family of terrestrial lizards was formerly, along with six other new families, considered a subfamily of Iguanidae (see Frost and Etheridge 1989). There are ten hoplocercid species, in three genera. Hoplocercids (which were previously known as morunasaurs) have a disjunct distribution in several places throughout the neotropics, including northwestern South America, Amazonia, eastern Brazil, and Panama.
Hoplocercids are spiny tailed lizards that attain sizes of up to 16 cm snout-vent length. Together with the other seven families that were previously part of Iguanidae (sensu lato), hoplocercids have pleurodont teeth, which distinguishes them from other members of the Iguania (agamids and chamaeleons). Hoplocercids are diagnosed by their extremely reduced vomers. In addition, they have enlarged lacrimal foramina; extensive skull rugosity; an anterior surangular foramen that is ventral to the posterior extremity of the dentary; a coronoid labial blade; and polycuspate marginal teeth. Each of these characters may be synapomorphies of Hoplocercidae, depending on who their closest relatives are.
Members of the type genus for this family, Hoplocercus, live primarily in dry forests. By contrast, Enyalioides and Morunasaurus species inhabit rain forests. Several species are known to use underground burrows. Males of Hoplocercus spinosus use their spiny tails as a defensive weapon when attacked. In addition, Hoplocercus males, though not truly burrowing, dig shallow holes in the soil, and use their tails to block the entrance. It is presumed that all species are oviparous, though the life history of members of this family are little known.
Hoplocercids 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 Hoplocercidae, 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 family status for these eight clades, including Hoplocercidae (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 Hoplocercidae is a member). Among the eight families of Iguanidae sensu lato, which includes Hoplocercidae, relationships are not resolved, although there is some support for a hoplocercid - iguanid (sensu stricto) sister relationship.
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).