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Animal Classification: Whiptail lizards, tegus, and relatives
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Class: Reptilia
Order: Squamata
Suborder: Lacertiformes
Family: Teiidae
Thumbnail description
Medium to large-sized diurnal, actively foraging, egg-laying, terrestrial lizards with well-developed limbs, long tails, and rectangular scales on the belly
Size
2Ã?¢ââ??‰â?¬Å?24 in (55Ã?¢ââ??‰â?¬Å?600 mm) snout-to-vent length; 5Ã?¢ââ??‰â?¬Å?51 in (120Ã?¢ââ??‰â?¬Å?1,300 mm) total length
Number of genera, species
9 genera; 18 species
Habitat
Forest, savanna, desert, and grassland
Conservation status
Extinct: 2 species; Critically Endangered: 1 species; Vulnerable: 1 species; Data Deficient: 2 species
Distribution
Middle North America (45Ã?â??Ã?° north) to southern South America (40Ã?â??Ã?° south), including Caribbean islands
Evolution and systematics
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 Kentropyx. 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), Callopistes (two species), and Crocodilurus (one species).
Physical characteristics
Teiids range from small (2.1 in [55 mm] snout-to-vent length, 4.7 in [120 mm] total length), such as in Cnemidophorus inornatus, to large (23.6 in [600 mm] snout-to-vent, 59 in [1,500] mm total length), such as in Tupinambis rufescens. They are fully limbed, terrestrial lizards that are diurnal, active foragers. All teiids lay eggs. Teiids are distinguished from Old World lacertids by having head scales not fused to the skull bones (fused in Lacertidae) and teeth that are solid on the base (hollow in Lacertidae). Teiid teeth are held to the jaws with cementum, a characteristic so distinctive that fossil teiid jawbones can be identified through the presence of this feature alone. Teiids are characterized as having small granular scales on the dorsum and rectangular plate-like scales on the belly. In one genus, Kentropyx, the belly scales are modified into pointed and keeled scales hypothesized to be an adaptation for climbing in bushy vegetation. Despite interesting morphological differences among genera, all teiids are relatively long bodied and long limbed with relatively narrow heads. All teiids have long tails, often more than 1.5 times body length. Fracture planes in each tail vertebra allow their tails to be easily broken. Teiids have good visual and olfactory systems. They have well-formed eyes and eyelids and long, forked tongues.
Distribution
Teiids are strictly New World lizards, distributed from the northern United States and through Mexico, Central America, and South America, except the extreme southern cone beyond approximately 45Ã?â??Ã?° latitude. Teiids, especially Ameiva and Cnemidophorus occur on many Caribbean islands. Teiids are widespread east of the Andes in South America and occur in the interandean valleys and coastal areas of Peru and southern Ecuador (e.g., Dicrodon, Callopistes flavipunctatus, and Ameiva). Callopistes maculatus occurs from northern to central Chile. Dracaena guianensis is Amazonian, whereas Dracaena paraguayensis inhabits the Pantanal ecoregion in Brazil, Bolivia, and Paraguay.
Habitat
As their continuous geographic range indicates, teiids are found in a variety of habitats, including wet and dry forests, primary and secondary forests, savannas, grasslands, deserts, and beaches. Regardless of habitat type, teiids need warm microhabitats where they can bask in direct sun to raise their body temperature for activity. For this reason, teiids usually are found using relatively open areas. In tropical forests, for example, they are frequently observed around treefall, along roads, and in clearings. The open habitats of deserts and beaches are well suited to the teiid lifestyle, and teiids occupy almost all such areas in North and South America within their latitudinal range. Habitat use by teiids is clearly tied to their thermal biology. In Costa Rica, one researcher demonstrated the effect of body size on the ability of three species of Ameiva to use different habitats. The smallest species could heat and cool rapidly and used the hottest, most open habitat. The largest species used the most shaded forest, where it would not be susceptible to overheating, and the medium-sized species used forest that was intermediate in shadiness. Juveniles of the large species shared microhabitat with adults of the small species, a finding that added support to the idea that thermoregulatory needs are coupled to habitat use among the sun-loving teiids.
Two genera of teiids are semiaquatic, Crocodilurus and Dracaena.
Behavior
Teiids are classic examples of actively foraging lizards. Teiids generally live in burrows they excavate themselves or that are made by other animals. A typical macroteiid day begins with the lizard basking in direct sun to raise its body temperature. Whiptails, especially Cnemidophorus and Ameiva, prefer relatively high body temperatures for activity, commonly measured in the field at 98.6Ã?â??Ã?°FÃ?¢ââ??‰â?¬Å?140Ã?â??Ã?°F (37Ã?â??Ã?°CÃ?¢ââ??‰â?¬Å?40Ã?â??Ã?°C). Once activity temperatures are achieved, a macroteiid embarks on long foraging or mate-seeking expeditions within its home range. Teiids maintain high body temperature while active by shuttling between sun and shade.
Feeding ecology and diet
Teiids are opportunistic feeders, and they are very good at finding and taking advantage of concentrated patches of prey such as insect larvae, ants, and termites that they dig out of the leaf litter or other cover. An individual may find several food sources during a foraging bout, and their meals are made up of different kinds of prey. Across the family, prey size correlates with body size. The large species of Ameiva, Teius, and the tegus (Tupinambis) include large amounts of fallen fruit in their diets. Tegus are omnivorous, consuming vertebrate prey and carrion as they encounter it. Tegus also are known to be important egg predators and have been reported to be the most important predator of caiman nests in the Venezuelan Llanos. Tegus have heterodont dentition as adults with pointed teeth in the front of their mouths for seizing prey and molariform teeth in the back of their jaws for crushing hard prey. Exceptions to the rule of opportunism among teiids are the caiman lizards (Dracaena spp.). These very large (more than 12 in [300 mm] snout-to-vent length), spectacular teiids are aquatic specialists that live around streams and swamps and feed primarily on snails. They have laterally compressed tails for swimming and foraging in water. Caiman lizards are named for the enlarged dorsal scales that look like crocodilian skin. Caiman lizards have a blunt head and molariform teeth for crushing their molluscan prey.
Reproductive biology
Teiids are not territorial, and several individuals' home ranges may overlap. Males are larger than females and compete for mates. Males follow receptive females and guard them against competing males. All teiids are egg layers. The number of eggs laid by females correlates with body size both among and within species. The largest species, Tupinambis merianae and T. rufescens, may lay approximately a dozen eggs when they reach sexual maturity, but by the time a female reaches maximum size, she may lay 30 or more eggs. The nesting ecology of most teiids is simple. Females deposit their clutches in the ground or within logs or debris. Tegus in southern South America, T. merianae, T. rufescens, and T. duseni, build elaborate nests of vegetation in their underground burrows into which they deposit their eggs. Females attend the nests throughout the incubation period. T. teguixin in northern South America lays its eggs in active termite mounds in trees.
The reproductive biology of whiptails and their allies is particularly noteworthy because of the existence of unisexual species. Unisexual species have no males, and individual lizards have no sperm. Mothers lay fertile eggs that develop into identical daughters, that is, clones. This mode of asexual reproduction is called parthenogenesis, and biologists sometimes refer to parthenogenetic species as parthenoforms. Parthenogenetic teiids arise when two sexual species hybridize. Parthenogenesis has been an important mode of speciation for whiptails of the genus Cnemidophorus, which contains at least 12 unisexual species. It is known, for example, that the unisexual desert grassland whiptail (C. uniparens) originated from hybridization events between the Texas spotted whiptail (C. gularis) and the little striped whiptail (C. inornatus). Hybridization events could easily have happened multiple times, hence parthenogenetic species exist in clonal complexes, as in the Laredo striped whip-tail (C. laredoensis) complex. Some parthenoforms have the typical condition of two sets of chromosomes (diploid), whereas others have three sets (triploid). The advantage of partheno-genesis is that when a mother produces identical daughters, each of her genes doubles in frequency in each descendant generation. Because all the individuals are reproducing females, teiid populations grow more rapidly than do populations of sexual species. Within the Teiidae, there is a parthenogenetic species of Kentropyx and one of Teius; parthenogenesis also is known in seven other families of squamates.
Conservation status
The Teiidae, for the most part, are common lizards that do well in a variety of habitats and in most circumstances appear to endure human influences. The Ameiva and Cnemidophorus endemic to Caribbean islands and the tupinambines subject to the pet trade and exotic leather trade are two major exceptions. Two species of Ameiva are categorized as Extinct by the IUCN, and another, the St. Croix ground lizard (Ameiva polops), is Critically Endangered. The St. Lucia whip-tail (Cnemidophorus vanzoi) is listed as Vulnerable. There are not enough data to determine the conservation status of Callopistes and other macroteiids that have been exploited for the pet trade. Island-dwelling lizards are clearly sensitive to human impact, and conservationists need to be aware of threats to teiids on islands or in otherwise restricted geographic ranges.
Several species of tegu are commercially exploited in very large numbers as pets or for skins. There is a long history of commercial trade in two species of tegu lizards (Tupinambis merianae and T. rufescens) from Argentina and Paraguay. In the 1980s, an average of 1.9 million tegus were traded yearly for the exotic skin trade, making tegus among the most exploited reptiles in the world. Tegu skins are prized for the pattern of tile-like belly scales, and they are used for cowboy boots, shoes, belts, and other exotic leather accessories in North America, Europe, and southeast Asia. Tegu lizards are listed in CITES Appendix II, and the trade is legal and monitored internationally. Harvest quotas are 1,000,000 for Argentina and 300,000 for Paraguay, and both countries have established management programs for the lizards that depend on trade controls and harvest monitoring. The caiman lizards (Dracaena spp.) have been exploited for their skins but not as extensively as the tegus. Tegus, Callopistes, and several species of Ameiva have appeared in the pet trade in large numbers. Mainland macroteiids appear to have a life history that enables their populations to withstand harvest by humans, but prudent conservation will require careful monitoring and management programs to ensure the take is sustainable over the long term.
Significance to humans
People have used tegu lizards for as long as there are historical records. South American Indians hunt and eat tegu, and tegu lizards are exploited commercially for their skins. In the areas where skins are traded, hunters sell the skins and consume the meat. Tegu fat is prized throughout Argentina and Paraguay for medicinal purposes. The trade in tegu lizards is economically important to local people and to the tanning industry. Thousands of hunters contribute to the total harvest of one million skins annually, and the export value of tegu skins is several millions of dollars.
The significance of the smaller teiids to people is less apparent, but these animals may still be important. Teiids are prey to myriad predators and themselves consume a variety of invertebrate prey and disperse seeds of the fruit they eat. Whiptails and their allies can occur at relatively high population densities and probably play an ecological role in their habitats. Cnemidophorus tigris has been studied in the Mojave desert, for example, and its populations have been shown to track its key habitat resources remarkably closely.
Species accounts
Giant ameiva
Six-lined racerunner
Desert grassland whiptail
Crocodile tegu
Paraguayan caiman lizard
Resources
Books:
Cogger, H. G., and R. G. Zweifel, editors. Reptiles and Amphibians. New York: Smithmark, 1992.
Degenhardt, W. G., C. W. Painter, and A. H. Price. Amphibians and Reptiles of New Mexico. Albuquerque: University of New Mexico Press, 1996.
Fitzgerald, L. A., J. M. Chani, and O. E. Donadio. "Tupinambis Lizards in Argentina: Implementing Management of a Traditionally Exploited Resource." In Neotropical Wildlife Use and Conservation, edited by J. G. Robinson and K. H. Redford. Chicago: University of Chicago Press, 1996.
Palmer, W. M., and A. L. Braswell. Reptiles of North Carolina. Chapel Hill: University of North Carolina Press, 1995.
Pianka, E. R., and L. J. Vitt. Lizards: Windows to the Evolution of Diversity. Berkeley: University of California Press, 2003.
Pough, F. H., R. M. Andrews, J. E. Cadle, M. L. Crump, A. H. Savitzky, and K. D. Wells. Herpetology. 2nd edition. Upper Saddle River, NJ: Prentice Hall, 2001.
Vitt, L. J, and E. R. Pianka. Lizards: Windows to the Evolution of Diversity. Berkeley: University of California Press, 2003.
Wright, J. W., and L. J. Vitt. Biology of Whiptail Lizards, Genus Cnemidophorus. Norman: Oklahoma Museum of Natural History, 1993.
Zug, G. R., L. J. Vitt, and J. L. Caldwell. Herpetology: An Introductory Biology of Amphibians and Reptiles. 2nd edition. San Diego: Academic Press, 2001.
Periodicals:
Beebe, W. "Field Notes on the Lizards of Kartabo, British Guiana, and Caripito, Venezuela: Part 3, Teiidae, Amphisbaenidae and Scincidae." Zoologica 30 (1945): 7Ã?¢ââ??‰â?¬Å?32.
Carpenter, Charles C. "Aggressive Behaviour and Social Dominance in the Six-lined Racerunner (Cnemidophorus sexlineatus)." Animal Behavior 8 (1960): 61Ã?¢ââ??‰â?¬Å?66.
Duellman, William E., and Richard G. Zweifel. "A Synopsis of the Lizards of the Sexlineatus Group (genus Cnemidophorus). "Bulletin of the American Museum of Natural History 123, no. 3 (1962): 155Ã?¢ââ??‰â?¬Å?210.
Echternacht, Arthur C. "Middle America Lizards of the Genus Ameiva (Teiidae) with Emphasis on Geographic Variation." Miscellaneous Publications of the Museum of Natural History of the University of Kansas, no. 55 (1971): 1Ã?¢ââ??‰â?¬Å?86.
Fitch, Henry S. "Natural History of the Six-lined Racerunner (Cnemidophorus sexlineatus)." University of Kansas Publication Museum of Natural History No. 11 (1958): 11Ã?¢ââ??‰â?¬Å?62.
Paulissen, M. A. "Diet of Adult and Juvenile Six-lined Racerunners, Cnemidophorus sexlineatus (Sauria: Teiidae)." Southwestern Naturalist 32, no. 3 (1987): 395Ã?¢ââ??‰â?¬Å?397. Ã?¢ââ??‰â?¬ÂÃ?¢ââ??‰â?¬Â. "Ontogenetic and Seasonal Shifts in Microhabitat Use by the Lizard Cnemidophorus sexlineatus. Copeia 1988, no. 4 (1988): 1021Ã?¢ââ??‰â?¬Å?1029. Ã?¢ââ??‰â?¬ÂÃ?¢ââ??‰â?¬Â. "Ontogenetic Comparison of Body Temperature Selection and Thermal Tolerance of Cnemidophorus sexlineatus." Journal of Herpetology 22, no. 4 (1988): 473Ã?¢ââ??‰â?¬Å?476. Ã?¢ââ??‰â?¬ÂÃ?¢ââ??‰â?¬Â. "Optimal Foraging and Intraspecific Diet Differences in the Lizard Cnemidophorus sexlineatus." Oecologia 71, no. 3 (1987): 439Ã?¢ââ??‰â?¬Å?446.
Peters, James A., Roberto Donoso-Barros, and Braulio Orejas-Miranda. "Catalogue of the Neotropical Squamata: Part II, Lizards and Amphisbaenians." United States National Museum Bulletin 297 (1970): viii, 293.
[Article by: Lee A. Fitzgerald, PhD]
