The whiptails, tegu lizards, and their allies make up the Teiidae, sister family to the Gymnophthalmidae. Throughout most of the twentieth century these families were classified together. Although many herpetologists still use the vernacular names, macroteiids and microteiids, these groups are now considered distinct families by practically all herpetologists. Teiidae and Gymnophthalmidae together form a lineage, Teioidea, which is sister to the Old World family Lacertidae (wall lizards, rock lizards, and their allies). Teiids and lacertids are so similar in appearance and ecology that it can be difficult to identify specimens to family without knowing their geographic origin. Because of their common ancestry, Teioidea (teiids plus gymnophthalmids) and Lacertidae belong to the suborder Lacertiformes.
An extinct subfamily of teiids, the polyglyphanodontines, existed in both North America and Mongolia in the Cretaceous period, an indication that ancient teiids once were widespread in the northern hemisphere. New and Old World polyglyphanodontines were distinguishable by the mid to late
Cretaceous, but there is no consensus among experts whether teiids evolved in the New or the Old World. It is agreed, however, that teiids were extinct in North America by the end of the Cretaceous, whereas the family diversified in tropical America. North American Cnemidophorus species must have recolonized North America from South American ancestors.
Two subfamilies of Teiidae, Teiinae and Tupinambinae, are recognized on the basis of several characteristics of the skull bones and mandible. Members of Teiinae are distributed in North, Central, and South America, whereas Tupinambinae occur only in South America. Teiinae includes the genera Ameiva, Teius, Cnemidophorus, Dicrodon, and Ken-tropyx. With 56 known species in 2001, and others being described from South America, Cnemidophorus accounts for more than half of all the teiids. Ameiva and Kentropyx are well represented, whereas Dicrodon and Teius each contain three named species. The subfamily Tupinambinae contains the genera Tupinambis (six species), Dracaena (two species), Cal-lopistes (two species), and Crocodilurus (one species).
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