Lizards of the United States

There are 8 families of lizards native to North America, with 155 species, including established introduced species. Known from the Triassic Period to the present, lizards today comprise the largest living group of reptiles. They come in a bewildering array of sizes, shapes, and colors, from tiny gecko species less than 3 inches long to the giant dragon lizard of Komodo nearly 10 feet long. Typical lizards superficially resemble salamanders, but their dry skin, clawed feet, and external ear openings quickly separate them from their distant moist skinned ancestors. Legless lizards may be confused with snakes, but unlike snakes, they possess moveable eyelids. The pattern and color of lizards vary greatly, males and females of the same species often show color differences, juveniles are frequnetly distinct from adults. Subspecies, too, may differ stikingly.

 

Lizards have varied life styles. Although generally diurnal, the majority of geckos, the night lizards, and the Gila monster are nocturnal. Only two species of venomous - the Gila Monster of the southwest and Mexico and the Beaded Lizard of Mexico. Courtship is brief, and fertilization is internal. Most lizards are egg layers, but occasionally young are born alive.

 

Gekkonidae (Geckos)

Three genera, with 5 species, are native to North America. Another 2 genera, with 5 species, have been introduced. Geckos typically have flattened bodies and short limbs. In addition to claws, many species hhave expanded toe pads. On the bottom of each toe pad are scales covered with a myriad of microscopic hairlike bristles. Minute suction cups on the tips of the bristles permit geckos to walk up walls and across ceilings. Most species lack moveable eyelids, instead the perpetually open eyes are protected by a transparent scale, the spectacle. The American genus Coleonyx is an exception, it has eyelids. Among diurnal species the pupil of the eye is round, in nocturnal species it is vertically elliptical. Many geckos appear fragile, their thin soft skin tears easily and the tail breaks so readily it seems cast off even before it is grasped. Among some populations many individuals will be found to have the tail in some stage of regeneration. Geckos are the most vocal of lizards. Voices vary from the sound that prompted the family name - the raucous "geh-oh" of the giant Asian Tokay Geckos - to the cricketlike chirps small species give when efending a feeding site. Most geckos lay two eggs at a time, Sphaerodactylus and Gonatodes lay only single eggs.

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Igunaidae (Iguanids)

There are 14 genera, with 44 species native to North America.

Another 4 genera, with 8 species, have been introduced.

Iguanids range from 4 to 72 inches in length. A typical iguanid is of moderate size, has 5 clawed toes on each of its 4 legs, and a long tail, its teeth are attached to the ledge on the inside of the jaw. Most species are either arboreal or terrestrial, they feed on insects and other invertebrates, but some, like Dipsosaurus and Sauromalus eat leaves, fruit, and blossoms. Except for a very few species that live in cool mountain habitats and give birth to living young, iguanids are egg layers. Clutches of many eggs or offspring are the rule, but Anolis lays only one eggs every couple of weeks.

Iguanids are possibly the most visually oriented of all lizards. They communicate at a distance by a show of color and behavioral signals. Mates are courted, territories defended, and interlopers driven off by elaborate and precisely timed combinations of head bobbing, body push-ups, and open mouthed displays that are unique to each species. Some further enhance the effect by curling the tail, inflating the chest and throat, or extending the throatfan, all of which expose a bright patch of color to the view of another lizard. Finally, many species exhibit intense color during the mating season.

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Anguidae (Anguid Lizards)

There are 5 species of Gerrhonotus and 3 species of Ophisarus in North America.

Anguid lizards are characterized by elongated, shiny, and stiff bodies and tails, closeable eyelids, external ear openings, and tiny (or absent) legs and toes. The stiffness is a result of an abundance of bony armor (osteoderms) in the skin. Many species are so stiff they could not expand to breathe were it not for a lengthwise flexible groove of soft granular scales along the sides. All the species in North America have this groove.

Most anguids are terrestrial or burrowing. While some species will bite, the primary defenses are fleeing, smearing an attacker with excrement, and giving up part of the tail. In some species the tail vertebrae have fracture planes along which the tail will readily break, leaving the writhing tip to be eaten by the predator while the rest of the lizard crawls to safety. In legless species, in which the tail may account for more than half the total length, the loss of a tail may give the impression that the lizard has been broken in two. Contrary to foklore, the part will not grow together again, but the body will grow a new tail in several weeks. Anguids are carnivores, they consume insects, small mammals, and other lizards. Most are egg layers, but a few mountain dwellers bear live young.

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Helodermatidae (Gila Monsters)

There is only 1 genera, with 2 species, in North America.

Gila monsters are heavy bodied, with short stout legs and a thick tail. With an abundance of food the tail becomes fat. During periods of scarcity, the tail may lose up to 20% of its bulk as the stored fat is used up. On the back and head are non overlapping beadlike scales of shiny black, pink, or yellow. The scales contain osteoderms, a sort of body armor.

Gila monsters are venomous carnivores that seems to rely more on taste and smell to locate their quarry than on sight. They have been observed tracking prey by tasting the ground with their long thick tongues. Their venom causes great pain, but rarely human death. It is the persistent grip of a Gila monster's jaw that is the single most important reason for handling these lizards carefully.

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Anniellidae (California Legess Lizards)

There are only 1 genus, with 1 species, found only in California and adjacent Baja California, Mexico.

These are long and slender lizards with moveable eyelids. Although legless, they still retain hip and shoulder bones internally. They are related to the anguid lizards, from which they differ by the absence of external ear openings, and body armor within the skin. Califronia legless lizards burrow in the loose soil and are seldom seen on the surface. They eat insects and the young are born alive.

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Xantusidae (Night Lizards)

There is only 1 genera with 3 species found in North America.

The night lizards are related to the geckos and like them have soft skin, a somewhat flattened body, and no moveable eyelids. But unike the geckos, the night lizards have small round scales on the back, large rectangular scales on the belly, and large shields on the head. The toes end in a sharp claw.

As the name implies, night lizards are mostly active at night, hiding in rocky crevices or under brush and leafy debris during the day. The light sensitive eyes have vertically elliptical pupils. Developing embryos are nourishd by a primitive placenta while in the mothers's oviduct. Young are born tail first and alive.

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Teiidae (Whiptail and Racerunner Lizards)

There are 16 species of Cnemidophorus that are native to North America, and 1 species of Ameiva that has been introduced.

Teiids are long slender lizards with long whiplike tails and well developed legs. Movements are characteristically rapid and jerky. They range from 4 to 48 inches in length. Typically they have small round, non overlapping scales on the back and large rectangular scales on the underside. There are no bony plates (oteoderms) in the skin. The large regular head shields are fused to the skull.

Whiptails are diurnal, terrestrial carnivores. Small species feed on insects and other invertebrates, while large species consume small mammals, birds and bird eggs, and other reptiles. Prey is located both by sight and by smell or taste, by means of a long deeply forked tongue. All teiids are egg layers. In most species, females produce fertile eggs only after breeding with males of the same species. However, there are true unisexual species among Cnemidophorus. All individuals are females, so there is no mating. A mature female lays fertile, but unfertilized, eggs that hatch into more females.

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Lacertidae (Typical Old World Lizards)

Only 1 species of Lacerta and 2 species of Podacris have been introduced to North America.

Lacertids are characterized by slender round bodies, well developed legs, and long tails. The back is covered with hexagonalsclaes, the underside scales are large and rectangular. The large head shields usually contain bony plates (osteoderms) and are not fused to the skull. Most species have moveable eyelids. Terrestrial species are variouly colored, while arboreal species are green. Males have slightly larger heads and may be differently colored from females. Lacertids are daytime hunters of insects, spiders, scorpions, and small vertebrates. All North American lacertids are egg layers.

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Scincidae (Skinks)

There are 15 species of 3 genera that inhabit North America.

A skink has a long cylindrical body and tail covered with smooth sleek scales containing bony plates (osteoderms). Terrestrial skinks have small legs, those adapted for burrowing have tiny legs or none. A clear window in the lower eyelid of the burrowing forms enables the animal to see when the eyelid is closed to keep out dirt. Fracture planes in the tails of many species allow the tail to break off easily when grasped by a predator. In such cases usually the tail is vividly colored to draw the attack of the predator away from the vulnerable body.

Skinks are diurnal. Most are insect eaters, but a few giant species are herbivorous. All species have thick oval tongues with a shallow notch at the tip. Most will nip the hand that catches them, and large species can inflict a painful bite. All North American species are egg laters. Females may tend the eggs during incubation.

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Amphisbaenid (Amphisbaenids)

Only 1 species and it is found only in Florida.

Amphisbaenids resemble earthworms in appearance. Body scales are fused into rings which encircle the body. Specialized for burrowing, family members lack external ear openings, have eyes buried under skin, and with the exception of one genus, Bipes, which has short front legs, they are limbless. Amphisbaenids live underground much of their lives feeding on insects and worms. The breeding biology is poorly known. Most seem to be egg layers.

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