Squamates—Part I. Lizards

Laurie J. Vitt , Janalee P. Caldwell , in Herpetology (Fourth Edition), 2014

Liolaemidae

Snow Swifts and Tree Iguanas

Classification: Squamata; Toxicofera; Iguania; Pleurodonta; Liolaemidae.

Sister taxon: The clade (Leiosauridae   +   Opluridae).

Content: Three genera, Ctenoblepharys, Liolaemus, and Phymaturus, with 1, 217, and 34 species, respectively.

Distribution: Southern South America including the Andes through Bolivia and into Peru (Fig. 21.45).

Characteristics: General characteristics shared with Tropiduridae. In addition, nasal conchae not fused to the roof of the nasal chamber; hemipenes unisulcate and weakly bicapitate, premaxillary spine overlapped by nasals. Meckel's groove in the mandible is variably fused. Interparietal scale enlarged, premaxillary spine not overlapped by nasals. Males lack femoral pores, and spinuate scale organs are absent. Hemipenes bisulcate, weakly to strongly bicapitate.

Biology: Liolaemids are somewhat smaller and smoother-scaled lizards when compared with tropidurids (Fig. 21.52). Many species include significant amounts of plant matter in their diets, and the number of independent origins of herbivory within these lizards may exceed all other origins of herbivory in squamates. Most liolaemids are oviparous with clutches ranging from 1–8 eggs, with larger species generally producing larger clutches. Some populations of the southern latitude and high-elevation species, such as Liolaemus magellanicus, are viviparous.

FIGURE 21.52. Representative liolaemid lizards. From top: Many-colored tree iguana Liolaemus multicolor (R. Espinoza); climber lizard Phymaturus spectabilis (R. Espinoza).

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Behavioral and Morphologic Adaptations

BRAD A. LOCK , in Reptile Medicine and Surgery (Second Edition), 2006

Squamates and Crocodilians

The tongues of many lizards are brightly colored or bicolored. Blue-tongued Skinks (Tiliqua scincoides) have a bright-blue tongue that they expose when harassed. Green Iguanas have a two-toned tongue, with the tip darker than the body. These colors do not represent cyanosis in the skink or an infection and necrosis in the iguana.

During the breeding season, many reptiles undergo a color or body shape change. Broad-headed Skinks develop an orange head (Figure 13-26) and Green Iguanas can have an overall orange or reddish appearance to the body, especially the head, dewlap, and forelimbs (Figure 13-27 ). These changes are associated with reproductive hormones and do not represent the reddening of the skin seen in septicemia. Many male lizards also have a hormonally induced increase in the size and activity of their femoral pore glands during the breeding season (see Figures 6-12 and 6-13). The femoral pores of male Green Iguanas increase greatly in size and exude a waxy material that contains pheromones. These waxy excretions, when applied to solid surfaces, reflect ultraviolet (UV) light. This is theorized to be another means of communication that serves to attract female iguanas. These pores can look like abscesses to the owner.

In snakes, the lower jaw is loosely connected by a ligament instead of a solid bony connection as is seen in most vertebrates (Figure 13-28). During feeding, the two halves of the mandible can move independently and stretch out of shape to aid in prehension and swallowing of food. After feeding, the snake manipulates the jaws by yawning to reposition the mandible back into normal position; this can take few minutes to accomplish. This should not be mistaken for a fracture of the mandibular symphysis.

Adult male Gharials (Gavialis gangeticus), a slender-snouted crocodilian from India, develop a large bulbous growth on the tip of snout during the breeding season (Figure 13-29). This growth resembles a "ghara," the Hindi word for pot. Several functions attributed to it are: a resonator that produces a loud buzzing noise during vocalization; a visual stimulus to females; and production of bubbles associated with sexual behavior. 34 The growth is a normal structure and does not represent a granuloma or tumor.

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LIZARDS

Javier Nevarez , in Manual of Exotic Pet Practice, 2009

Reproductive System

Sex determination may not be easily accomplished in some reptile species. Others have sexual dimorphism that allows differentiation of males and females based on external characteristics. In the green iguanas, males tend to have large heads with big dewlaps, operculum scales, and dorsal spines, all considered to be male-associated characteristics. Females have smaller heads and smaller dewlaps. Other lizard species may also have increased ornamentation in the males in the form of colors, crests, spines, casques, and other exaggerated external features as compared with the females (Figures 8-4 and 8-5 ). This distinction in masculine versus feminine characteristics is not evident in all lizard species. Instead, veterinarians must rely on more precise ways to differentiate the sexes. Large femoral pores can easily be observed in the adult male of many species (see Figure 8-2). Females have smaller femoral pores as compared to the males (see Figure 8-1). Another distinction comes from the presence of the male copulatory organs, the hemipenes, which are located on the ventral aspect of the base of the tail caudal to the location of the vent. A hemipenal bulge can be observed on adult males of some species. The hemipenes are a purely copulatory organ with no association with the urinary system. Therefore, the copulatory organs can be amputated in cases of trauma or unresolved paraphimosis. This occurs with lizards and other reptiles.

Reproduction in lizards is stimulated by environmental effects, such as temperature, humidity, and photoperiod. The presence of natural substrates, such as soil, may stimulate reproduction in females. Before folliculogenesis, the females may decrease food consumption and become anorectic. Anorexia is often the first sign that a female is reproductively active. Males have paired internal testes that will increase in size during the reproductive season, and females have paired ovaries with follicles that grow to considerable size during the reproductive season. Females also can produce and lay infertile eggs in the absence of a male. Egg retention/binding is a common presenting symptom in some female iguanas. Frequently, egg retention is associated with inappropriate husbandry and diet, and an ovariohysterectomy is the treatment of choice in these patients. Aggressive behavior may be observed in intact adult lizards, especially during the reproductive season. Early sterilization may prevent hormonally induced behavior in adulthood, but the owner must understand the treatment may not be effective.

The birthing and reproductive methods of lizards are quite varied. Lizards can be oviparous, ovoviparous, or parthenogenic. Oviparous species lay eggs that require incubation until the hatching of the young. Many species dig nests in the ground where they lay the eggs. Ovoviparous species give birth to live animals without the need for laying an egg. Parthenogenic species do not require mating to produce young (e.g., whiptail lizards [Cnemidophorus tigris]). Instead, the females are able to reproduce by themselves. Green iguanas and bearded dragons are oviparous species. Blue-tongued skinks (Tiliqua spp.) are ovoviviparous. Chameleons can be oviparous or ovoviparous.

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Species Accounts

In Cyclura, 2012

Description

The Acklin's iguana (C. r. nuchalis) (Figure 2.46) is one of three poorly-defined C. rileyi subspecies that are small in size compared to other rock iguanas. The Acklin's iguana can be distinguished from the other rileyi by several scale features, including four scale rows between the frontal and prefrontal scales, three rows of loreal scales, and eight superciliary scales. Caudal verticals are not as enlarged as they are in either the White Cay or San Salvador iguanas, and the enlarged postsacral scales form a shorter row. The Acklin's iguana also has more femoral pores than the other two subspecies (41–55) (Schwartz and Carey, 1977; Hayes and Montanucci, 2000; Carter and Hayes, 2004).

FIGURE 2.46. Acklin's iguana (Cyclura rileyi nuchalis).

 Photo by Joe Wasilewski.

Adults are dark black to bluish-gray in color with orange-brown to blackish marbling (Figure 2.47). The ventral surface is gray with orange-brown marbling on the chest. Juvenile Acklin's iguanas are very similar in coloration to San Salvador iguanas, but with a darker mid-dorsal zone in the dorsal pale band. Body color ranges from tan to black and the head is brownish. The venter is gray and the gular area is dirty yellow (Schwartz and Carey, 1977).

FIGURE 2.47. Adult female Acklin's iguana.

 Photo by Joe Wasilewski.

The generic name Cyclura is derived from the Greek words cyclos, meaning circular, and urus, meaning tail, after the thick-ringed tail characteristic of all iguanas in the genus. The specific name rileyi refers to Joseph Harley Riley, an American ornithologist. The subspecific epithet nuchalis means neck, and refers to the thick scalation around the neck.

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Lizards

STEPHEN L. BARTEN , in Reptile Medicine and Surgery (Second Edition), 2006

Integument

Lizards have relatively thick skin with ectodermal scales formed by folding of the epidermis and outer dermal layers. Epidermal growth is cyclic, and lizards undergo regular periods of shedding or ecdysis, during which the skin comes off in large pieces in most lizards rather than in one piece as seen in snakes. Some species eat their sloughed skin. Normal shedding is one indication of good health. The frequency of ecdysis varies with species, temperature, humidity, state of nutrition, and rate of growth. Rapidly growing juveniles may shed every 2 weeks. 30 Wounds and skin infections cause more frequent shed cycles.

The skin contains few glands. Many lizards, notably iguanas, have femoral pores in a single row on the ventral aspect of the thigh (see Figures 6-12 and 6-13), and many geckos have both femoral and precloacal pores, the latter in a V-shaped row anterior to the cloaca. These tend to be larger in mature males.

Chromatophores are abundant in species that have rapid color changes, such as Chamaeleo spp. and Anolis spp. Control of the chromatophores may be hormonal, neurologic, or both. Chromatophores may react to stimulation from light or changes in temperature. 5

Osteoderms, or dermal bony plates, are present in Gila Monsters, Beaded Lizards, some skinks, legless lizards, and Girdle-tailed Lizards. These are usually confined to the back and sides.

Dewlaps, spines, crests, and horns may be present and often are secondary sex characteristics, more prominent in males. Spines serve a protective function in Bearded Dragons, Horned Lizards and the Moloch (Moloch horridus).

A lateral skin fold is usually present between front and hind legs. This is a convenient site for the injection of subcutaneous fluids.

Claws in large species like iguanas and monitors are large and well developed with sharp points. These must be trimmed at regular intervals to prevent deep scratches that would occur inadvertently even with casual handling. The nails should be trimmed before a physical examination.

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Biology and Diseases of Reptiles

Dorcas P. O'Rourke DVM, MS, DACLAM , Kvin Lertpiriyapong DVM, PhD , in Laboratory Animal Medicine (Third Edition), 2015

C Reproduction

Sexual dimorphism can be very distinct in certain species of reptiles, making sex determination a relatively straightforward process; however, visual sex determination can be difficult or nearly impossible in certain species in which males and females have very similar morphological features. Sex determination in reptiles can be accomplished using several methods, with the preferred method varying among species. Male box turtles and tortoises of many species have a concaved plastron that serves to stabilize the male when he mounts the female during breeding. The tail of male turtles is longer and the vent more distally located on the tail than it is in females. Male red-eared sliders and other species have elongated claws on their forelegs; these claws are used to stroke the sides of the female's head during courtship. Males of several lizard species, such as iguanas, have a large row of femoral pores on the inside of the hindlegs. The femoral pores of females are smaller or absent. Male snakes have a longer, thicker, more gradually tapering tail than do females ( Rossi and Rossi, 1995; Mattison, 1998). A single, fleshy penis is present in male turtles and crocodilians (Fig. 19.11a). Snakes and lizards have paired, membranous hemipenes, which lie in the base of the tail and are everted during copulation (only one hemipenis is used during copulation) (Fig. 19.11b). In species such as the bearded dragon, the hemipenes may produce noticeable ventral bulges in the proximal tail that can often be used to distinguish male from female. Species with hemipenes can be sexed by gently inserting a smooth, blunt probe into the cloaca and directing the probe caudally. If the snake is a male, the probe will easily pass within the inverted hemipenis for a distance of 3–4 scale rows or more (Rossi and Rossi, 1995). Other sexing methods include manually everting the hemipenis of neonatal snakes, and injecting saline into the tail behind the hemipenes to hydrostatically evert them. Crocodilians can be sexed by digitally palpating the cloaca (Rossi and Rossi, 1995; DeNardo, 1996).

Figure 19.11. Male turtles have a single fleshy penis (a). Snakes have membranous paired hemipenes (b).

Reproductive strategies vary among reptile species. As breeding concludes, the male garter snake (Thamnophis sirtalis) leaves a solidified plug of ejaculate in the female's cloaca to prevent subsequent breeding by another male (Zug, 1993). The whiptail lizard, Aspidoscelis uniparens, is parthenogenetic. Postovulatory females act as surrogate males, courting preovulatory females and thereby stimulating ovulation and production of genetically identical offspring. All turtles and crocodilians lay eggs; some lizards and many snakes bear live young. Anoles lay one egg at a time throughout the breeding season, while iguanas lay 20–40 eggs in a single clutch. Rat snakes lay five to 44 eggs per breeding, and garter snakes deliver up to 80 live young at a time (Mattison, 1991; Rossi, 1992). Some species of day gecko (Phelsuma spp.) lay two eggs at a time. The female lies on her back and uses her hindlegs to roll the pliable eggs into spheres, which she presses together until they harden. She then hides the eggs in a selected hiding place to incubate (Henkel and Schmidt, 1995).

All female pythons provide protection as well as thermal and hydric benefits to their developing offspring by wrapping around their eggs. Certain python species shiver to produce metabolic heat and facilitate egg incubation (Stahlschmidt and DeNardo, 2010). Female crocodilians vigorously guard their nests throughout the incubation period. When the young are ready to emerge, they begin vocalizing. The female assists the young in digging out of the nest, and in some cases will pick them up and carry them to the water. Some females remain with their brood for up to 2 years and defend them from potential predators (McIlhenny, 1987; Lang, 1987; Burghardt and Layne, 1995).

Incubation temperature determines the sex of offspring in many reptile species. Alligator eggs incubated at lower temperatures produce females, and higher temperatures produce males. In the wild, temperature differentials across the nest result in a mixture of both sexes.

In the laboratory, most reptile eggs can be artificially incubated. The eggs should be removed and placed in an incubation chamber (usually a plastic shoe box with a loose-fitting lid), taking care to preserve their original orientation. A moist bed of sphagnum moss or vermiculite can serve as an incubation medium. Humidity should be about 90–100%, and temperatures should average about 30°C (Rossi, 1992). Alligators require slightly higher temperatures. Many snake eggs hatch 2–3 months after being laid (Fig. 19.12).

Figure 19.12. Many snake eggs hatch within 2–3 months after being laid. Eggs can be incubated in moist sphagnum moss.

 Image courtesy of Fred Hawkins.

Neonatal reptiles are essentially miniature reproductions of adults, fully capable of surviving on their own. Some species may require diet modification; however, most eat essentially the same food type as the adults.

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Neuroendocrinology of Reptilian Reproductive Behavior

Michele A. Johnson , Juli Wade , in Hormones and Reproduction of Vertebrates: Reptiles, 2011

5.2 Development in Reptiles with Alternative Reproductive Morphs

In U. ornatus, T and P4 are important factors in the organization of differences between the two male morphs (Hews, Knapp, & Moore, 1994; Hews & Moore, 1996; Moore et al., 1998). This conclusion is based on both measurements of endogenous hormones and studies in which hormones were manipulated. Castration of juvenile males produced more orange males than a control group, while castrated juvenile males given T implants were more likely to be orange-blue than control males (Hews et al., 1994). This study also found the same pattern of results when 30-day-old intact males were given T implants or blank capsules, indicating that the critical period for the role of T or its metabolites in morph differentiation may continue beyond 30 days. Further work determined that T does not influence dewlap color after post-hatching day 60 (Hews & Moore, 1996 ), suggesting that the critical period for this trait has ended by this developmental stage. Treatments with T or its metabolite DHT are equally effective for the development of male sexual traits, including dewlap color, waxy femoral pore secretions, and hemipene-related tissues, while DHT is required for full expression of the blue belly patches ( Hews & Moore, 1995).

Progesterone also plays an important role in the organization of morph phenotypes. Manipulations of P4 or T at hatching result in differing morphs (Moore et al., 1998). Progesterone may operate independently of T or, alternatively, it may be the initial trigger of differentiation, with T operating later in development (Moore et al., 1998). In-vitro incubation demonstrated that, during the period between embryonic day 30 through hatching, P4 is released by the adrenal glands and T from the testes (Jennings, Painter, & Moore, 2004). This early production of T from U. ornatus gonads contrasts with results from turtles (Pieau, Mignot, Dorizzi, & Guichard, 1982; White & Thomas, 1992a) and crocodiles (Smith & Joss, 1994), in which levels of T are very low in early post-hatching periods.

Galapagos marine iguanas provide an example of a species in which developmental and environmental conditions affect reproductive behavior via changes in circulating hormones. In this species, males can be successful territory holders only after achieving a certain body size, but this threshold is affected by climate conditions and population density (Wikelski & Trillmich, 1997) such that, when territories are available, smaller males may adopt territorial behavior. The ontogenetic switches between sneaker and satellite, and satellite and territorial strategies can be imitated via manipulation of T. When exposed to increased T, satellite males begin to defend territories and sneaker males begin to openly court females (Wikelski, Steiger, Gall, & Nelson, 2005), behaviors more typical of larger males. These changes do not increase the reproductive success of manipulated males, however, as they experience more frequent fights with other, larger males and expend time and energy performing courtship displays that are largely ignored by females (Wikelski et al., 2005). Further, when T is blocked, territorial males decrease their defensive and courtship behaviors (Wikelski et al., 2005).

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Natural History

In Cyclura, 2012

Social Behavior

Rock iguanas are social animals that live in either large group settings (e.g., Bahamian iguanas, Turks and Caicos iguanas) or in temporary aggregations with more dispersed lifestyles (e.g., Jamaican iguanas, Mona Island iguanas). In either social setting, there must be a communication system to decrease aggression, yet still maintain a healthy, breeding population.

Rock iguanas communicate in a number of ways, both chemically and visually. The femoral pores on the underside of the hind legs secrete a mixture of lipids and proteins that are thought to be used to attract mates and mark territories (Alberts, 1993). Iguanas use their tongues and the Jacobson's organ in the roof of the mouth to identify scent marks. This process, called chemoreception, delivers chemical signals from the tongue directly to the brain via the vomeronasal nerve. Iguanas may also use feces to communicate. It is quite common to observe iguanas tongue-flicking the feces of conspecifics, and chemical signals in feces potentially communicate territory, reproductive condition, and health and body condition of the signaler.

The other primary mode of communication in rock iguanas is visual signals. The most important form of communication is the head bob, in which the head is raised and lowered in a stereotypical, species-specific bobbing pattern (Martins and Lamont, 1998). These displays are used in almost all social interactions and vary according to the behavioral context in which they are used. Head bobs are most often seen in the aggressive encounters that accompany territorial maintenance, and during the breeding season. In general, males tend to display much more frequently than females (Martins and Lacy, 2004). In some species, appeasement head bobs are employed to reduce aggression in group settings (Iverson, 1979; Martins and Lacy, 2004). Displays vary between species, populations, and even individuals, often containing information about an animal's identity (Martins and Lamont, 1998).

Rock iguanas also use body posturing to communicate. In aggressive encounters and territorial disputes, large males will often turn their bodies sideways to appear larger to conspecifics. They may also stand high on their feet and fill their bodies with air to look as large as possible. Dorsal crest spines on the back not only help iguanas acquire more ultraviolet light to aid calcium absorption, but also make them appear larger during aggressive encounters. Body posturing is also observed in submissive displays, usually in females and low-ranking males. Such displays usually involve the iguana getting its body as close to the ground as possible, as if trying to hide. The base of the tail is often raised, possibly allowing dominant animals to tongue-flick the vent area in order to assess breeding condition or social status (J. Lemm, personal observation).

Fights are common, especially during the breeding season as males defend territories and females. Head bobs, body posturing, and gaping serve as a first defense, but often escalate into physical pushing matches to contest territories or mates. Fighting is often observed on the boundary between two territories during the breeding season. Male Cuban iguanas will sit face to face, gape, hiss, wriggle the tail tip, and lunge at one another (J. Lemm, personal observation) (Figure 3.13). Fights are usually short-lived and primarily involve tail whips to the body and jaw-wrestling, in which both males have their mouths open, grasping each other's jowls as they push each other back and forth. The thorn-like projections on the faces of male rock iguanas serve as protection in these instances. On very rare occasions during intense fights when neither iguana backs down, males bite one another with tremendous force, potentially breaking tails and sometimes severing limbs in very bloody battles. On one occasion, a male Cuban iguana even pushed a rival male off a cliff to his death (J. Lemm, personal observation).

FIGURE 3.13. Gaping is a common form of aggressive display in rock iguanas.

Hatchling and juvenile iguanas show similar behavior to adult iguanas. Dominance is established early in life, with the larger animals usually emerging as the most dominant. Head bobbing, gaping, jaw wrestling, and fighting are commonly observed under both captive and wild conditions.

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Ecology and Conservation of the Imperiled Dunes Sagebrush Lizard: An Ecological Specialist in a Threatened Ecosystem

Lee A. Fitzgerald , ... Mickey R. Parker , in Reference Module in Earth Systems and Environmental Sciences, 2022

Life history

Description

The Dunes Sagebrush Lizard is a member of the Phrynosomatidae, which consists of small to medium sized lizards distributed mainly in North America. The genus Sceloporus is known as the spiny lizards with all species having over lapping dorsal scales with a pronounced keel that ends in a spine posteriorly on each scale. Species of this genus most often exhibit territoriality, with males maintaining larger home ranges than females. In general, species in the genus Sceloporus use a sit and wait strategy of foraging.

The Dunes Sagebrush Lizard is small with males averaging 54.5   mm snout-vent length (SVL) with a maximum of 75   mm, and females averaging 53.8   mm with a maximum of 63   mm SVL (Degenhardt and Jones, 1972). The dorsal coloration is light brown with an ill-defined pair of longitudinal lighter stripes extending down the sides of the torso. Males have large paired blue belly patches and occasionally have scattered blue scales on the throat. Females develop orange markings on the sides of the face, neck, and body when they become gravid (Hibbitts and Hibbitts, 2015). S. arenicolus has 8 or more scales separating the medial ends of the femoral pores, which is an identifying characteristic of this species. Enlarged scales partially cover the ear openings and the front digits are relatively long, traits that are probably adaptive in this sand-diving and sand-burrowing species.

Reproduction and nesting

The Dunes Sagebrush Lizard can be found throughout the year with two activity peaks in late spring and mid-summer (Leavitt, 2019). Like most lizards, onset of reproduction is cued by increasing temperatures and day length in spring. Courtship and mating occur mostly during May and June, which also corresponds to the peak of activity in the third week of June (Leavitt, 2019). Like other members of their genus and family, female Dunes Sagebrush Lizards tend to migrate out of their core home range to nest (Hill and Fitzgerald, 2007). During a radio-tracking study of 20 females, 10 nesting sites were found and two nests were discovered with eggs. Nesting females dispersed to adjacent blowouts or other portions of larger blowout areas immediately before nesting. Nesting occurred at night and was often characterized by a late afternoon movement outside of the normal range of the lizard. Females dug nest tunnels into the steep side of a blowout until they reached moist soil at a depth of 11 or 19   cm. Another nest was found in 2011 in a blowout (Ryberg et al., 2012). The observations, taken together, indicated females select nest sites close to the moisture horizon in the sandy soil and choose sites where sand grain size composition is relatively coarse compared to surrounding areas in their home range (Ryberg et al., 2012). Females may reproduce once or twice in a season, laying an average of 5 eggs per clutch in mid-June, and again in late July or early August (Fitzgerald and Painter, 2009; Ryberg et al., 2015). Hatchlings appear in early July and a portion will reach sexual maturity in their first spring (about 10   months of age). Individuals that hatch later or grow slower may not breed until their second spring. The lifespan of the Dunes Sagebrush Lizard is typically 3   years and rarely 5 or more years.

The Dunes Sagebrush Lizard is adept at burrowing and diving into sand. Individuals dive into the sand to hide or escape predation and may wait for prey while mostly buried. Typically, individuals bury themselves just under the surface of the sand to spend the night. In many cases a small portion of their back and tail are still visible from the surface. The nesting excavations made by females are arduous, and the females may stay beneath the surface for hours and move around underneath the surface. Coarse sand probably makes nesting, burrowing, and sand-diving easier. Sand that is too fine or too compact may interfere with breathing and may not allow sufficient diffusion of oxygen (Ryberg and Fitzgerald, 2015).

Diet and predators

The Dunes Sagebrush Lizard is a sit-and-wait ambush forager, and its diet is typical of small North American lizard species, consisting mostly of ants, grasshoppers and crickets, spiders, beetles, and other arthropods (Fitzgerald and Painter unpublished data). Several predators may take Dunes Sagebrush Lizards as prey, including a variety of snake species (e.g., Young et al., 2018), avian predators such as Loggerhead Shrikes (Lanius ludovicianus) and Greater Roadrunners (Geococcyx californianus) (Hathcock and Hill, 2019), and mammalian predators. One radio-tracking study found Coachwhip Snakes (Masticophis flagellum) consumed 20% of radio-tagged gravid females (Hill and Fitzgerald, 2007). In a separate radio-tracking study of 36 individuals, one was preyed on by a Glossy Snake (Arizona elegans) and three others by Coachwhip Snakes (Young et al., 2018).

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Lizards

In Clinical Anatomy and Physiology of Exotic Species, 2005

GENERAL EXTERNAL ANATOMY

In general lizards are elongated and circular in cross-section, but arboreal chameleons are vertically compressed and some lizards, like the Bearded dragon (Pogona vitticeps), are horizontally compressed (Fig. 4.1).

Family: Iguanidae

These are moderate to large in size and include many herbivorous species. They have a large, laterally compressed body with nuchal and dorsal crest, large gular pouch, and conspicuous subtympanic plate. The tail is up to three times the snout-to-vent length and can be whip like. Femoral pores are prominent in the male. Males are generally more brightly colored, some displaying an orange hue in the mating season. The coloring of females tends to wash out with age. Iguanas are pleurodont and have nasal salt glands. Several species have a prominent parietal eye. Nearly all are oviparous. Many have partitions in the colon to slow down food ingesta ( Evans 1986; Pough 1998b).

Examples:

Green iguana (Iguana iguana) (Fig. 4.2), Marine iguana (Amblyrhynchus cristatus), Chuckwalla (Sauromalus spp.), Basilisk (Basilicus spp.).

Family: Agamidae

These are mainly terrestrial lizards with well-developed limbs and are the old world equivalent of Iguanidae. They have acrodont teeth and some species have almost rodent-like incisors at the front of the jaw. Some species have sexually dimorphic crests and spines. They are mainly oviparous. The South-east Asian Flying lizard (Draco volans) is the only lizard capable of gliding flight. This is achieved by having elongated ribs supporting webs of skin which can be opened like a fan for gliding. The Australian Frilled lizard has a frill which it can erect when danger threatens (Pough 1998b).

Examples:

Flying lizard (Draco volans), Frilled lizard (Chlamydosaurus kingii), Water dragon (Physignathus sp.) (Fig. 4.3), Bearded dragon (Pogona vitticeps).

Family: Chameleonidae

These are arboreal with a laterally compressed body and are mainly diurnal and insectivorous. The upper and lower eyelid is fused to form a pyramid mound with the eye as the aperture in the center. Each eye is capable of independent movement and they use accommodation to measure distance. The eye lens is like a telephoto lens and the large retina and high number of cones provide the chameleon with large visual images of its prey (Evans 1986).

The tongue is rapidly extensible to a distance of at least twice the animal's trunk length and is used for apprehending insect prey. The hyoglossal skeleton is modified into an extension called the processus entoglossus, which at rest keeps the tongue folded in pleats at the back of the mouth. A powerful accelerator muscle propels the tongue forward like a spring. The tongue tip is also sticky to catch the prey. Jacobson's organ is poorly developed.

Chameleons have very specialized skulls with their parietal crest raised into a casque. They have lost the skull kinesis seen in other lizards, which was presumably made redundant by the powerful tongue (Pough 1998e). The acrodont teeth, unlike in other species, do not have pleurodont teeth rostrally as the premaxilla is quite reduced with few teeth there at all. The chameleons' laterally compressed bodies and prehensile feet enable them to keep their center of gravity over a narrow support base. Their vertical limbs and highly mobile pectoral girdle gives them a longer step and the ability to reach forward more onto branches. The feet are zygodactyl, with toes fused together and opposed in groups of two and three (Fig. 4.12). The tail is prehensile and usually tightly coiled distally, with no autotomy. Rapid color changes are possible. Sexual dimorphism is common. They can be oviparous or viviparous (Bellairs 1969a, 1969f; Pough 1998b).

Examples:

Yemen veiled chameleon (Chamaeleo calyptratus) (Fig. 4.4), Parson's chameleon (Calumma parsonii).

Family: Gekkonidae/Eublepharidae

These are crepuscular or nocturnal insectivores with a flattened head and body. Most have adhesive toe pads which contain rows of tiny overlapping scales ventrally called lamellae. Each lamella has tiny, branching hairs called setae which can number up to one million in some gecko species. The ends of these setae are spatulate and it is the friction between these endings that creates the adhesive qualities of the feet and enables them to walk across ceilings and glass, even holding on by only one foot (Bellairs 1969a; Evans 1986; Pough 1998b).

Many have loose skin and fat pads in the tail. Autotomy is common. Many lack eyelids which, like snakes, are fused to form a spectacle. They are not sexually dimorphic. They are oviparous and lay very hard-shelled eggs. Eublepharids are unusual in that they are terrestrial and have eyelids. They lack the adhesive lamellae and so are unable to climb.

Examples:

Leopard gecko (Eublepharis macularius), Tokay gecko (Gekko gecko), Standing's day gecko (Phelsuma standingi).

Family: Varanidae

These are the giants of the lizard world and can reach a length of 3.6 m (Komodo dragon). Often called monitor lizards or, in Australia, "goannas." They are stocky with smooth scales. The tongue is forked for half its length and, as in snakes, is used more for exploration than tasting (Evans 1986). In some species ossification of the hemipenes can be seen on radiographs. Despite their size they are active predators with higher metabolic rates than most other lizards (Bennett, AF 1972). They are oviparous and have no autotomy (Pough 1998b).

Examples:

Komodo dragon (Varanus komodoensis), Bosc monitor (Varanus exanthematicus).

Family: Scincidae

These are a large terrestrial family that live mostly on or underground. They are small to medium in size (5-20 cm), are smooth scaled and are glossy in appearance. Osteoderms are present beneath the scales and the young often have blue tails (Pough 1998b). The limbs are short in relation to the body and some species are completely limbless. (Different species may have four limbs, two limbs or no limbs) (Fig. 4.5). They have a prominent ear opening; eyelids are fused to form a spectacle in some. The tail can be lost and regenerates. Some species are oviparous; some are viviparous with well-developed placentation. Except for the herbivorous arboreal Solomon Island skink they are mainly insectivorous (Evans 1986; Pough 1998b).

Examples:

Blue-tongued skinks (Tiliqua spp.), Solomon Island skink (Corucia zebrata).

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https://www.sciencedirect.com/science/article/pii/B9780702027826500077