Excerpted From

Excerpted from ©2003 by the Regents of the University of California. All rights reserved. May not be copied or reused without express written permission of the publisher. click here to BUY THIS BOOK CHAPTER 10 FROM RACERUNNERS TO NIGHT LIZARDS This tropical African lacertid, In this chapter we introduce the highly active teiids Holaspis guentheri, often sleeps with its tail coiled, and lacertids, the diminutive gymnophthalmids, and resembling an armored millipede. (Louis Porras) the secretive, long-lived xantusiids. Teiids, lacertids, and gymnophthalmids are in constant motion, maintaining a distance between themselves and other creatures—including humans—and frequently looking back to keep tabs on what could, after all, be a potential predator. Any sudden move by an observer, and the lizard darts off; although it immediately initiates foraging behavior again, its vigilance never ceases. 193 These are the lizards that dominate terrestrial habitats (with notable exceptions), discriminating between prey in the New World and much of the Old World (exclud- and nonprey using chemical cues; and many, but not all, ing Australia). Most of these lizards live in open habi- are active at high body temperatures. tats—even Amazonian forest teiids, such as Dracaena and Xantusiids, or night lizards, differ considerably from Crocodilurus, favor large swamps or edges of rivers with teiids, gymnophthalmids, and lacertids, and their phylo- sun exposure. Tiny gymnophthalmids appear at first genetic position is less certain. They may be the sister glance to be exceptions because many are found in undis- taxon to Lacertiformes, but they could be more closely al- turbed rain forest. However, when scale is considered, lied to the Annulata, the group containing, among other most live in the open: a patch of leaf litter in western Ama- zonia is as much an open habitat to Prionodactylus eigen- manni as the bank of a small stream flowing through the same forest is to Neusticurus ecpleopus. Teiids, gymnophthalmids, and lacertids (all of which form the clade Lacertiformes) are tied together evolu- tionarily because they share a common ancestor. Teiids are most closely related to gymnophthalmids, and both are presently restricted to the New World. Lacertids, the sister taxon to the teiid-gymnophthalmid clade, are an Old World group. Ecological counterparts in their respective habitats, lacertiforms share a number of identifying fea- tures: they have elongate, streamlined bodies compared with many iguanians; alert and often fast moving, they Pantodactylus schreibersii is a common gymnophthalmid in forage actively, primarily on the surface of the ground Brazilian cerrado. (Janalee Caldwell) The gymnophthalmid Micrablepharus atticolus lives in tailings of leafcutter ant nests. (Laurie Vitt) LIZARD DIVERSITY 194 things, wormlike amphisbaenians (see chapter 9). An- the dorsal surface, with large, rectangular scales forming other possibility is that they are related to Gekkota. We distinct transverse rows ventrally. All teiids have fully include xantusiids here recognizing that future studies formed legs and a fairly distinctive overall morphology may place them elsewhere within the evolutionary tree consisting of streamlined bodies, long tails, relatively of lizard families. Xantusiids live in enclosed spaces. pointed snout, eyelids, and long hind limbs. They are ac- Some occupy crevices in rocks (Xantusia henshawi), others tive foragers and lay eggs. (X. vigilis) live under decaying remains of Joshua trees or Teiids occur throughout the southern and western con- clumps of large beargrass, Nolina bigelovi. Xantusiid eyes tinental United States, across Mexico and Central Amer- are capped over like those of most geckos; they have el- ica, on many Caribbean islands, and into much of South liptical pupils and are active in dark places. Their body America (excluding the high Andes and extreme south- temperatures while active are considerably lower than ern parts of South America). Nine genera are recog- those of Lacertiformes. nized: Ameiva, Callopistes, Cnemidophorus, Crocodilurus, Dicrodon, Dracaena, Kentropyx, Teius, and Tupinambis (Presch 1974). One genus, Cnemidophorus, with 56 named TEIIDAE species (Wright 1993), has undergone an extensive adap- The teiids we know today are a New World family, eco- tive radiation. Ameiva and Kentropyx are well represented logical counterparts of Old World lacertids. Historically, also, but Tupinambis, Callopistes, Teius, Dracaena, and Di- teiids had a wider distribution, at least in the Northern crodon contain only a few species. Crocodilurus is mono- Hemisphere. Their northern distribution is restricted to typic, that is, represented by a single species, C. lacertinus. deserts, the southern half of the Great Plains, and the Teiids are divided into two subfamilies, Teiinae (Ameiva, coastal plain of the southeastern United States. A now ex- Cnemidophorus, Dicrodon, Kentropyx, and Teius) and Tupi- tinct group, polyglyphanodontines, was diverse in the late nambinae (the remaining four genera). Teiids vary in Cretaceous of North America, and they also occurred in body size, ranging from the small whiptail Cnemidopho- the Upper Cretaceous of Mongolia. The fossil record in- rus inornatus (55 mm SVL) to large tegus, Tupinambis dicates that New and Old World polyglyphanodontines (500 mm SVL), and caiman lizards, Dracaena (approx. had diverged considerably from each other by mid to late 300–450 mm SVL). Cretaceous. A faunal exchange during early Cretaceous The 56-plus species of Cnemidophorus (= carrying leg sent some from east to west; others, however, went from armor), commonly known as racerunners or whiptails, west to east. The fossil record does not clearly indicate range from southern Idaho through Central America whether teiids originated in the Old or New World, and the Caribbean all the way to Argentina. They reach though ancient teiids apparently colonized much of the their largest body sizes in northern South America and on New World. By the end of the Cretaceous, all Northern some Caribbean islands, with size generally diminishing Hemisphere teiids had gone extinct (Nydam 2000). Mod- as latitude increases (although exceptions exist: C. tigris, ern teiids, therefore, diversified from ancestors remain- for example, is smaller in southern parts of its geographic ing in subtropical and tropical areas of the New World, range). Several species of Cnemidophorus remain un- where they achieved the remarkable evolutionary success named, including one found in Manaus, Brazil. Many we see today. A single genus, Cnemidophorus, reinvaded “species” of whiptails are unisexual; in these, males do not and diversified in the northern half of the New World. exist and females reproduce by parthenogenesis. As soon Several characteristics distinguish teiids from other as a female reaches sexual maturity, she begins produc- lacertiforms. Teiid head scales are separate from skull ing daughters that are genetically identical to herself (see bones; those of lacertids are fused to the skull. Teiid teeth chapter 6). Parthenogenesis occurs in some other teiids have solid bases and are “glued” to jaw bones with ce- (e.g., Kentropyx) as well, and in some other squamate mentum; those of lacertids are hollow, and cementum is families. absent. Indeed, cementum is such a prominent teiid char- Herpetologists have had difficulty identifying whiptails acter that it can be used to distinguish fossil teiid jaw- and working out their relationships. As Charles Lowe bones from those of all other fossil lizards. Additional points out in his insightful introduction to Biology of characteristics include generally small, granular scales on Whiptail Lizards (Genus Cnemidophorus) (Wright and RACERUNNERS TO NIGHT LIZARDS 195 Vitt 1993), the famous herpetologist Edward Drinker example, in Cnemidophorus inornatus and C. neomexi- Cope considered this genus the most difficult in all of her- canus; Christiansen 1971). In tropical environments where petology. Yet Cope had seen only the tip of the iceberg: annual temperatures are relatively constant, activity and parthenogenetic Cnemidophorus were not discovered un- reproduction can occur nearly year round (as in C. ocel- til 1958 (not published until 1962), adding a new element lifer in northeastern Brazil; Vitt 1983). of confusion to the genus. A North American species, Cnemidophorus tigris, ranges Discovery of parthenogenesis in East Asian Lacerta by from southern Idaho through Sonora and Baja Califor- Ilya Darevsky (1958) sent the American herpetologists nia. Because of its wide distribution, it exemplifies geo- Richard Zweifel and Charles Lowe deep into their col- graphic variation in ecological traits. In the north, C. tigris lections searching for the answer to a question implicit in are active at both lower body temperatures and lower am- an observation first made by Sherman Minton (1958); why bient environmental temperatures than in the south. Their were there no males in Cnemidophorus tesselatus? Indeed, seasonal period of activity is also shorter in the north. Fre- not only did C. tesselatus prove to be parthenogenetic, but quencies of broken regenerated tails are higher in the a swarm of parthenogenetic Cnemidophorus were found south (Pianka 1970a). Most whiptails eat a variety of in- to occur all across the southwestern United States and sects (particularly termites) and spiders, but some, such as northern Mexico, all very difficult to sort out. Zweifel and C. lemniscatus, add fruits to their diet, and a few, such as

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