Behavior and morphological adaptations of reptiles (Proceedings)


There are greater than 6500 species of extant reptiles with a wide variety of behaviors and structural morphologies designed to allow them to escape notice or fight off enemies, reproduce, obtain food and adapt to their environment. This lecture describes some commonly seen and some less commonly seen behaviors and morphological adaptations in reptiles.

There are greater than 6500 species of extant reptiles with a wide variety of behaviors and structural morphologies designed to allow them to escape notice or fight off enemies, reproduce, obtain food and adapt to their environment. This lecture describes some commonly seen and some less commonly seen behaviors and morphological adaptations in reptiles. These behaviors and adaptations are normal for the particular species or group discussed but to the unfamiliar hobbyist or clinician may appear to be a sign of disease or trauma.

Defensive behaviors

Catalepsy, death feigning, tonic immobility

This category describes a condition or state of external unresponsiveness to stimulation. This can be seen as maintenance of a rigid posture or of a flaccid condition. This behavior occurs commonly in some groups of snakes (e.g. hognose snakes, False spitting cobras) and has been described in lizards and crocodilians.

Hognose snakes (Heterodon sp.) are well known for their complex death feigning behavior. When first disturbed hognose snakes will exhibit an elaborate bluff display consisting of an exaggerated S-coil, loud hissing and false strikes. The tail is often tightly coiled and can be elevated. If grasped or further harassed, these snakes will begin to writhe violently with the mouth hung limply open and often will excrete urates & feces. Violent writhing continues for a short time and then the snakes assumes an inverted, limp posture, usually with the mouth open and the tongue hanging out. If the snakes is turned over onto its ventrum, it will immediately turn back onto its dorsum. When the threat is removed, the hognose snake slowly rights itself and crawls away. Pseudoxenodontines, closely related to the hognose snakes, and false spitting cobras (Hemachatus sp.) are also well known for their elaborate death feigning behavior that closely resembles that of the hognose snakes. Assumption of a rigid posture that could be misinterpreted as an injury has been described in Trachyboa boulengeri and the bandy bandy (vermicllia anulata).

For lizards and crocodilians, chameleons in the genus Brookesia and leaf tailed geckos (Uroplatus sp) exhibit tonic immobility when threatened as does the microteiid, echinosaura horrida. Death feigning occurs in at least one teiid (Callopistis flavipunctatus), one Cordylid (Gerrhosaurus major) and three monitor species. Hatchling caiman crocodylus vocalize, bite and struggle on land but feign death if grasped under water.

The evolution of death feigning and tonic immobility may be related to removal of movement; a widespread class of stimuli among vertebrates, that elicits killing behavior by a predator. Reduction or elimination of the cues for killing might provide the potential prey animal with later opportunities for escape, especially from predators that transport whole, immobile prey to their young (e.g. raptors, canids). Alternative explanations involve the observation that many of the snakes that death feign eat frogs and toads, have enlarged adrenal glands, and at least one (Heterodon sp) exhibits bradycardia during death feigning. The author suggests that death feigning behavior is facilitated by typically high levels of circulating catecholamines and that it might represent a non-adaptive consequence of toad-eating. Evidence against this is that the death feigning response occurs repeatedly if a threat is rapidly presented and removed from a hognose snake and that the false spitting cobra remains alert and ready to bite while death feigning.

Squirting blood from the eyes and or nostrils

A number of species of horned lizards (Phrynosoma sp) and at least one species of boid (Tropidophis sp) squirt or exude blood from the eyes and or nostrils as a defensive mechanism. In horned lizards the ability to squirt blood is derived from modifications to the cephalic circulation. Restriction of blood flow from the head results in increased vascular pressure. Subsequent contraction, of the protrusure oculi muscles, ruptures capillaries in and around the eyes which causes a thin stream of blood to be ejected up to 2 meters. This defensive mechanism seems to be an especially effective deterrent to some mammalian predators (e.g. Canids).

Tail display

Tail displays as a defense mechanism are fairly common being seen in pipe snakes (Anilliidae), shield tailed snakes (Uropeltidae), ring necked snakes (Colubridae), burrowing pythons, sand boas and rubber boas (Boidae), coral snakes and shield nosed snakes (Elapidae) as well as a few lizard species. This behavior probably developed to divert a predators attack away from the vulnerable head to the more disposable tail.

The display varies between the different species and families but usually involves hiding the head beneath the body (coral snakes, shield tailed snakes) or within a coiled up body (sand boas, burrowing python). The tail is then waved around in the air, coiled tightly or moved in a manner that mimics a striking head (rubber boas). Many species (pipe snakes, coral snakes, ring necked snakes) have a brightly colored contrasting ventrum that is exposed when the tail is displayed. This can serve to startle the predator and give the snake a chance to escape; the tails of many of these individuals display scars from previous attacks that attest to the effectiveness of this defensive behavior. In many species, especially the coral snakes, the tail display is accompanied by writhing and cloacal discharge.

These displays can be misinterpreted as an animal in pain or possible neurologic disease.

Everting hemipenes

Another defense mechanism that is employed by many reptiles and is especially well developed in some boids (blood python) elapids (coral snakes) and monitor species, is eversion of one or both hemipenes. When harassed, these animals will often writhe violently, empty there cloacal contents and evert one or both hemipenes. Since this behavior is often associated with manipulation of the reptile by the owner the novice owner may misinterpret this as an injury; the owner has caused the abdominal organs to prolapse. In the vast majority of cases the hempenis or hemipenes will reduce back into the tail upon cessation of the stimuli. A similar phenomena can occur during defecation.

Puffing up body, throat, hissing

A portion of many defensive displays in reptiles and amphibians involve bluffs and threats. One of the more common of these behaviors is increasing the body size by inflating the lungs and puffing up the body. Subsequently, the air is rapidly expelled from the lungs in a long loud hiss. This display behavior is very common in many families of snakes and lizards. Pine snakes have developed a septum at the glottal opening (glottal keel) the serves to amplify the sound produced during hissing. The behavior can deter attack by a predator by being extremely vigorous as in many snakes and lizards or by being passive serving to increase the body size beyond the gap of many predators as in the Uromastyx sp.

For the herpetoculturist, this rapid influx and efflux of air may resemble an animal with respiratory disease. Inflation of the throat region in bearded dragons, chameleons, monitors and boid and pine snakes can look like excess fluid build up.

As an adjunct to the above, many reptiles especially monitors and rat snakes (Asian rat snakes) will flatten the caudal area of the head and the cranial are of the neck to increase size in a threat display. This display also has the effect of uncovering bright colors of the skin that are normally concealed by the scales. These bright colors can startle an attacker and give the animal time to escape. Many of the Asian rat snakes and monitors will also hold the head in a bent position and move the tongue slowly and stiffly during the display. This can be misinterpreted as respiratory disease or injury to the muscles or nerves of the head and neck.

Chameleon color change-dropping from branch

Chameleons are for the most part strictly diurnal animals that cease all movement as soon as the sun goes down or the cage lights are turned out. Most species will sleep at the ends of thin branches and their color becomes blanched almost to a white. If they are disturbed in the wild or captivity at night they drop as if dead from the branch. This is an effective escape behavior that allows the chameleon to avoid predation but the uninformed owner may think the color change is abnormal or that the fall from the branch indicates a sick animal.

Chameleons are also noted for and are especially adept at color change due to an elaborate system of chromatophores in the dermis. If two unfamiliar chameleons, two male chameleons or a non-receptive female is placed with a courting male a violent color change can occur. This may be interpreted as illness. These changes are behaviorally and hormonally induced and illness secondary to stress can ensue if husbandry changes are not instituted.

Fragile skin in geckos

Most geckos species are nocturnal, have special scansorial foot pads for adhesion to walls and ceilings and rely on crypsis or rapid locomotion for escape from predators such as snakes, owls and bats. Tail autonomy (see later) is almost ubiquitous. A number of species like the common house gecko (Aristelliger hechti), Gehyra mutilata, Pachydactylus manquensis, Phelsuma sp, Teratoscincus scincus and Ctenotus lenista have evolved very fragile skin. These species will loose large portions of epidermis even when handled gently. In species that have been studied such as the bronze gecko (Ailuronyx seychellensis) of the Seychelles and the Madagascan genus Geckolepis the skin on the animals back is weakened by gaps in the fibrous structure of the skin. When predators grasp the lizard most of the skin, except for a thin layer that remains to protect underlying tissues, tears away. This is probably an escape mechanism similar in function to tail loss and does not indicate a nutritional, endocrine or other similar disease.

Balling up

Another defense mechanism similar to hiding the head under a loop of coils, is hiding the head in the center of a ball of coils. A number of boids employ this method of defense. The most well known of these boid species is the ball python (Python regius) of West Africa. A number of other species including the African burrowing python (Calabaria rehinhardii) and the rosy boas (Lichanura sp.) exhibit this behavior.

When harassed these boids roll into a tight ball with the vulnerable head in the middle of the coils. Protection from trauma is the obvious reason for this behavior. Field observations of Lichanura trivirgata support a less obvious reason for the behavior. On two separate occasions when these small boas were encountered under rocks, the animals balled up and rolled out of reach of the observer into nearby crevices. This locomotor use of the balling behavior may be used to escape predators, like ringtails, that live in the area and eat snakes. A similar behavior is exhibited by the armadillo girdled tailed lizard (Cordylus cataphractus) of Africa. When threatened in the open this lizard will grasp the heavily armored tail in its mouth and form a circle to shield its more vulnerable under parts from attack.

Tail vibrating

The vibrating of the tail in a disturbed rattlesnake is an almost universally known defensive behavior. Many other venomous and non-venomous snakes also employ tail vibrating as part of a defensive repertoire. Tail vibration as a behavior is usually seen as part of an overall defensive strategy that involves striking, writhing and emptying of the cloacal contents. The behavior is characterized by a rabid tail movement or vibration that if done in dry leaves can produce a buzz that is audible to the human ear.

This behavior is restricted to and widespread among snakes and is exhibited by many commonly kept colubrids such as king snakes, bull and pine snakes, rat snakes, racers and coachwhips. It is also a common behavior of many species of vipers. In the bushmaster (Lachesis muta) a large Central and South American viper sound production is enhanced by the peculiar shape and arrangement of the terminal scales of the tail. While the behavior would most likely not be misinterpreted as disease a veterinarian may get a call because a person believes the snake to be a rattlesnake.

Tail loss/autonomy

This defense mechanism is a part of broad category of defenses designed to divert an attack away from a vulnerable part of the body and allow escape. While autonomy is common in invertebrates it occurs, in vertebrates, only in some salamanders, several rodents and the majority of lizards. At least some species in all families except the Agamidae, Chamaeleontidae, Helodermatidae, Lanthonodidae, Xenosauridae and Varanidae exhibit total or partial tail autonomy when grasped by a predator. After the tail is shed it will continue to wiggle often vigorously distracting the attacker and allowing the lizard an opportunity to escape.

In most species that exhibit this behavior anatomic modifications are present in the tail that serve to direct where fractures occur. The ruptures occur at so called fracture planes that are located within a single vertebral body not between vertebral bodies. This division in the vertebrae corresponds to a similar division between two muscle segments and this zone of weakness is maintained even to the level of the skin. Blood loss is minimal in autonomy and for those lizards that escape an attack the tail will regrow over a period of months. The lost vertebrae are replaced by a cartilaginous rod and the muscles and scales that regrow are irregular in shape and may differ somewhat in color.

Tail loss while not a sign of disease has costs associated with it. The tail is often a common site for fat deposition and some lizards use the tail in grasping or social interactions. An owner should be informed that males may not breed without tails and females may not have sufficient energy stores to produce viable young during the period between tail loss and regrowth.

Salt glands

Accessory salt glands are present in all orders of reptiles including many commonly kept as pets such as green iguanas and Uromastyx sp. These glands function to rid the animals of excess salts accumulated, during feeding (marine iguanas), as a result of the environment (sea turtles), or as a way of conserving water (iguanas, desert species). Clinically, the salts are sneezed out of the nares often in a fine spray and white deposits are seen around the nares or on the glass of the caging. The owner may report this as respiratory or fungal disease to the practitioner.

The salt water crocodile (Crocodylus porosus) also has fairly extensive salt glands located in the tongue. These glands serve the same function as those glands located in the nares and can be seen as a discoloration of the tongue that may be misinterpreted as pathology.

The reptilian kidney can not cope with excess salts absorbed from sea water. Sea snakes and file snakes possess a modified salivary gland located beneath the tongue. Excess salt is excreted into the tongue sheath and when the snake protrudes the tongue the salt is extruded into the sea. The homolopsines (South American water snakes) possess a similar gland located in the front of the roof of the mouth. Sea turtle salt glands are modified tear glands and excess salts are excreted from the corners of the eyes.


Reptiles do not have the ability to internally regulate their body temperature. Normally, the body temperature of an exposed reptile quickly approaches that of the environment. Because of this a number of strategies are employed to maintain the body temperature at a desired level. When too cool, reptiles bask in the sun and then shuttle between a cool shaded area and an open sunny one. Many nocturnal species will expose portions of their body to the sunlight or hide under bark or rocks and absorb heat by transfer from these objects to themselves (thigmothermy). Some reptiles may also limit activity to certain times (morning and evening) thus avoiding extremes of temperature. Length of basking is controlled hormonally via the pineal gland also known as the third eye.

A few of the behaviors associated with thermoregulation could be misinterpreted as disease, trauma or pathology. Many reptiles will begin morning basking by exposing only the head from a crevice or burrow. Heat uptake in this situation is enhanced by hormonally controlled darkening of the skin through the dispersal of melanin. Seeing this color change in a pet animal could be interpreted as disease or trauma. Other strategies used are to move all or part of the body off the ground to avoid picking up heat radiated from the surface. As an example, a lacertid lizard that lives in the Namib Desert of Africa raises a foreleg and the opposite hind leg simultaneously, balancing on the other two legs. This allows the skin of the elevated feet to cool. The lizard then alternates the lifting and lowering of the diagonal pairs of legs as long as it is exposed to the hot sand. This behavior could be interpreted as pain or neurologic disease. The pineal or third eye itself may be mistaken for a defective scale or an injury to the head. Lastly, many tortoises and some monitor species sun themselves with the head and neck fully extended and the forelimbs arranged limply. They can and do look as if they are dead.

Although not strictly associated with thermoregulation, Asian water dragons (Physignathous concincinus) will commonly rest or sleep underwater. While this behavior is normal owners may believe their pet has drowned or is drowning.

Reproductive behavior

Squamate (lizard and snake) reproduction and courtship

During the breeding season many reptiles undergo a color or body shape change. Broad headed skinks develop an orange head and iguanas can have an overall orange or reddish appearance to the body especially the head, dewlap and forelimbs. 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 there femoral pore glands during the breeding season. The femoral pores of green iguanas increase greatly in size and exude a waxy material containing pheromones which serve to attract female iguanas. These pores can look like abscesses to the owner.

Part of the behavioral repertoire in many iguanids includes social displays such as head bobbing, push-ups, dewlap extension and aggression (biting, tail lashing). Head bobbing is employed by both male and female iguanas with males generally displaying this behavior more frequently and with greater variety. Females bob in a jerky, erratic motion. They most commonly bob when irritated by a male iguana or when warning another iguana or owner away from food or a basking area.

Male iguanas have several different types of head bobs. All the different head bobs are executed in fluid smooth motions. The bobs are generally up and down in motion, can be fast or slow and may include some side to side movement. The shudder bob, is a warning and is characterized by a rapid vibration of the head in an up-down-sideways motion. At the completion of the movement, the head is held up for a few seconds and then a very deliberate up and down bob is performed. Subordinate males tend to bob more like females.

Head bobbing in an aggressive territorial male is accompanied by a full, rigid extension of the dewlap and extended legs lifting the body high off the ground. The body is presented laterally to object in question and the lungs are inflated. A very characteristic stilted, stiff gait is employed by the animal. This behavior and posture serves to increase the size of the silhouette presented by the iguana to the offending object.

Another behavior associated with aggression is the open mouth treat display (gaping). The mouth is opened very wide exposing the bright pink oral mucosa. The tongue will often be visible and in an extended, arched configuration and a low guttural hiss may accompany the display. These are strong warning and threat signs that may lead to full bites and tail lashing if not heeded. A modification of the gaping threat is employed by some iguanas when involved in aggressive or dominance encounters. These animals will sit with the body tensed and the mouth slightly opened. An iguana in this posture may bite at the slightest provocation.

It inconvenient to split aggressive behavior in iguanas into two categories: defensive and offensive aggression. Defensive aggression is most often associated with a threat such as another iguana or human attempting to displace the animal from a basking site, perch or food; grabs the iguana or invades the animals perceived territory. The behaviors most commonly associated with defensive aggression include the puffed-up, sideways stance, extended dewlap, open mouth threat and tail lashing; if provoked further they may bite.

Offensive aggression is associated with the breeding season or in the establishment of dominance hierarchies and usually involves sexually mature males. These iguanas will often stalk the human females in the household biting them in an attempt to breed. Many of these attacks are directed at the neck and face because male iguanas bite and hold onto the neck of the female to achieve intromission. These male iguanas will often view the human male in the household as competition and will perform head bobs and tail lashing at an increased rate towards that person. Since the person does not leave the iguanas "territory" these displays will often escalate into biting attacks. Although not the whole story, increases in aggression are generally associated with increases in testosterone. This breeding season aggression usually lasts for3-4 months and can occur anytime of the year but generally is from November-April.

Suggested ways to deal with breeding season aggression have been many and varied. Certain colors of cloths and time of month (menses/ovulation) for females can trigger attacks. Owners should be aware of what they are wearing and doing during attacks so they can become aware of a pattern if one exists. Adopting an aggressive stance or attitude can sometimes help to deter attacks. Reducing the photoperiod to 10 hours of light per day will sometimes reduce the frequency and vigorousness of attacks. Changing the room and or the cage the iguana lives in sometimes will help to reduce aggression as can providing a surrogate iguana, such as a towel a stuffed toy or a sock, to mate with has worked well for some iguana owners.

Castration can also be a helpful adjunct to one or more of the above mentioned suggestions for reducing aggression in mature male green iguanas. In one recent study, 16 mature male green iguanas were randomly placed into one of three experimental groups. One group of 5 animals was castrated before the onset of breeding season aggression, a second group of 5 animals was castrated during the breeding season when exhibiting aggressive behavior and a third group of 6 animals served as the control group; these animals were sham operated but were not castrated. There was a statistically significant reduction in aggressive behavior between the group castrated prior to breeding season but not between the group castrated during breeding season and the control, non-castrated group. Subsequently, the author has castrated more than 60 male green iguanas. Follow up information up to 3 years later has shown that castration has reduced or eliminated aggression in about 70% of the animals.

The courtship behavior of many squamates involves the male grasping and biting the female in the neck and upper back region. This behavior can range from mild, causing the female no harm, to vigorous with the creation of open bleeding wounds. In snakes the males will often grasp the female by the neck with an open mouth. This behavior can look like fighting or in the case of some snake species can appear as if one animal is tryingto the eat the other.

Incubation behavior in pythons

Egg brooding or shivering thermogenisis is a phenomenon well known to herpetologists and herpetoculturists. This behavior is characterized by a female python coiled tightly around a clutch of eggs and exhibiting rhythmic muscular contractions (shivering) of the body which produce sufficient heat to maintain a relatively constant temperature in the egg mass over a fairly wide ambient temperature range. This behavior has been reported for (species 289, table) and may be universal in pythons.

In studies with captive pythons, rhythmic contractions begin when the temperature of the egg mass falls below the desired temperature (approx 30°C). At 30°C no contractions occur; the female simply remains coiled around the egg mass. As the ambient temperature falls the female python begins to shiver and the number of contractions increases as the temperature drops up to a maximum of approximately 30 contractions per minute. Monitoring of the temperature of the egg mass revealed a constant differential of 5-7 °C (9-15 °F) between the egg mass and the surrounding environment and maintenance of the egg mass at 30°C

This behavior can resemble a parasitic infection (mites causing irritation) a nutritional disease (hypocalcemia) or a neuromuscular disease especially as the female python will often continue to shiver even if the egg mass is removed. To stop the shivering behavior the animal should be moved to a clean cage and the old cage thoroughly cleaned and the substrate changed to remove all scent of the egg mass.

This behavior is energetically expensive to the females; who may loose up to half of their body weight during incubation and may require 3 years to regain enough body condition to breed again. The advantages to the species are that the eggs develop rapidly and the species who demonstrate egg brooding can reproduce successfully in cooler climates.

Turtle reproduction and courtship

The social interactions of turtles and tortoises associated with reproduction and courtship usually involve head-bobbing, males butting and biting the females to immobilize them, and then mounting the females shell from the rear. These behaviors are often accompanied by bellowing or whistling vocalizations.

In order to achieve intromission the male must incline his body towards the vertical, to varying degrees in different species. The extreme is seen in the box turtles, who may incline beyond the vertical.

This reproductive and courtship behaviors maybe seen as fighting and the vocalizations as pain or injury by the owners. Seeing a box turtle inclined backwards may look as if he is stuck in the females shell.

Geckos licking eyes

The vast majority of gecko species lack eyelids and instead have a evolved a spectacle analogous to that of snakes. A common behavior exhibited by most species is to clean the spectacle by licking it with the tongue. This behavior is normal but rule outs could include ulcers, retained spectacle or any kind of irritation.

Arm waving in bearded dragons

Arm waving is seen in very young bearded dragons and can be present within a few days of hatching. It seems to serve both as an intraspecies signal, for identification as a bearded dragon, and as a submissive behavior. This behavior persists commonly in adult females and in subordinate males during aggressive encounters. This behavior could be misinterpreted as a painful or injured limb.

Caudal luring

A behavior to attract and capture food using the tail as a lure is a behavior most common among vipers but has been suggested in boids (Madagascan ground boa, boa constrictor) and elapids. In most cases the tip of the tail is a bright color contrasting with that of the rest of body and in some instances is modified into the shape of an insect some (Bothrops bilineatus) are swollen and pink.

The tail is waved in a rhythmic fashion and will often imitate the movement of an invertebrate. Lizards, mice, frogs and toads are attracted to within striking distance and captured and eaten. This behavior occurs in both juvenile and adult animals of various species.

Stargazing in boids and crotalids

An interesting behavior that has been noted in captive boids and some crotalids is the adoption of a posture where the neck is bent in such a manner as to cause the head to be tilted upwards (stargazing). A similar posture is seen in snakes suffering from parasitic, viral bacterial or fungal CNS disease. The difference between the two postures is that the animals without disease revert to a normal posture when disturbed or manipulated and the ones with disease do not.

This behavior may be a feeding posture modified for captivity. Many animals are fed from top opening cages. Even with those cages that are front opening the prey items are often introduced from above. The snakes may have adapted to looking up for food in their search for prey.

Morphological adaptations (turtles)

A number of normal structures that are morphological adaptations have evolved in the chelonia that could be seen by an owner or practitioner as a disease process or traumatic injury.

Mud and musk turtles (Kinosternidae), box turtles (Terrepene, Emydidae) and hinge backed tortoises (Kinixys sp) have evolved a hinge or hinges in the plastron or carapace so that the animal can close itself in for protection from predators and equally important from lose of moisture. The hinges vary in number and location. In most species of mud turtles two hinges are present, on cranial and one caudal, that allow the turtles to completely close itself within the shell. Musk turtles have one cranially located hinge that serves to protect the front limbs and the head. Box turtles also have one hinge in the plastron but it is located further back than in musk turtles. This location allows the front and back halves of the plastron to close; completely sealing the animal within the shell. Hinge backed tortoises have a hinge located on either side of the carapace which affords protection of the hindquarters. Other species that have developed one or more hinges include African mud turtles, Asian box turtles and Madagascan and Egyptian tortoises.

A lesser degree of movement is found among certain species of pond and river turtles. Asian leaf turtles and neotropical wood turtles have a partial hinging of the plastron with ligamentous rather than bony connections between the plastron and the carapace. This gives flexibility to the plastron but the shell cannot be closed. This adaptation appears to have evolved to allow these species to lay their exceptionally large eggs which could not otherwise fit through the shell opening. In a number of these species (cane turtle, spiny turtle) only mature females develop the kinetic plastron.

Certain large headed, aggressive species such as snapping turtles, big headed turtles and Mexican musk turtles also have movable plastrons due to ligamentous rather than bony connections between the plastron and the carapace. In these species the flexibility of the plastron allows the large head to be retracted within the shell. With the jaws open and the head protected by the shell a formidable and nearly impregnable defensive is provided.

Similarly, the pancake tortoise of East Africa (Malachochersus tornieri) has a flat, soft shell as an adult. This condition is due to permanent open spaces or fontanels between the bony plates of the carapace and the plastron. These fontanels increase in size as the tortoises grow. These species live in rock outcroppings and are good climbers. When threatened they wedge themselves in rock crevices and are very difficult to extract. All of the above are normal structural modifications and should not be interpreted as traumatic injury or as a result of nutritional or other metabolic disease.

Many species of side necked turtles (genus) can exude fluid from the plastron, generally in the area of the bridge. It is unknown if this fluid is for defense or a pheromone for courtship and reproduction. This should not be mistaken for fluid loss secondary to septicemia or trauma.

A morphological adaptation for attracting and capturing prey is possessed by the alligator snapping turtle ( Malacochersus tornieri). This bifurcate modification of the tongue is wormlike in appearance and can be made to wiggle by contractions of the muscular base that it is attached to. This appendage can look like an oral parasite to the laymen.

Morphological adaptations (lizards/crocodilians/snakes)

The tongues of many lizards are very colorful or of two different colors. Blue tongued skinks have a bright blue tongue that they expose when harassed. Iguanas have a two toned tongue; the tip being darker than the body. These colors do not represent cyanosis in the skink or an infection and necrosis in the iguana.

Many gecko species have bilateral structures, located in the ventro-lateral cervical region, that are involved in calcium metabolism and storage. These structures are called endolymphatic glands or chalk glands. During the breeding season these glands will often hypertrophy and fill with calcium in preparation for egg laying. These structures are very prominent on radiographs and may be misinterpreted as an abnormal mass.

Male gharials, a slender snouted crocodilian from India, develop a large bulbous growth on the tip of snout during the breeding season. This growth is a normal structure and does not represent a granuloma or tumor.

In snakes the lower jaw is loosely connected by a ligament instead of a solid bony connection as is seen in most vertebrates. 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.