Origin of Reptiles


Comparative Nitrogen Excretion
Lead your line of heroes to glory! Hind limbs were used for clinging on to the rocks and cliffs and 3 digits of fore limbs also had curved claws, an adaptation for clinging. I don't want a "God" like that! The Titans are depicted in art with their legs replaced by bodies of snakes for the same reason: The reason for this is that they want to see how we will act when we are not being manipulated.



The red-eared sliders also breathe during locomotion, but they had smaller breaths during locomotion than during small pauses between locomotion bouts, indicating that there may be mechanical interference between the limb movements and the breathing apparatus. Box turtles have also been observed to breathe while completely sealed up inside their shells Landberg et al.

Most reptiles lack a secondary palate, meaning that they must hold their breath while swallowing. Crocodilians have evolved a bony secondary palate that allows them to continue breathing while remaining submerged and protect their brains from getting kicked in by struggling prey. Skinks family Scincidae also have evolved a bony secondary palate to varying degrees.

Snakes have a different approach and extend their trachea instead. Their tracheal extension sticks out like a fleshy straw. By thrusting their windpipe into the throat, these animals can swallow large prey without suffering from asphyxiation, despite the fact that swallowing may take several hours.

Land-dwelling reptiles, such as snakes and lizards, excrete nitrogenous wastes in pasty or dry form as crystals of uric acid Towle Two small kidneys are used in excretion. Snakes have hinged upper and lower jaws, which move independently.

These jaws stretch when unhinged, allowing snakes to swallow large prey. Saliva begins to digest food before it reaches the stomach, which is basically an enlargement at the end of the esophagus where digestion can slowly proceed Towle Crocodilians have modified salivary glands on their tongue salt glands , used for excreting excess salt from their body, although they are non-functioning in alligators and caimans.

Crocodilians are known to swallow stones, gastroliths "stomach-stones" , which help to crush up the bones of their prey. The crocodile stomach is divided into two chambers, the first one is described as being powerful and muscular, like a bird gizzard, and this is where the gastroliths are found. The other stomach has the most acidic digestive system of any animal, and it can digest mostly everything from their prey; bones, feathers, and horns. Reptiles have an advanced nervous system compared to amphibians.

They have twelve pairs of cranial nerves. The brain is relatively small. The tongue of a snake includes highly sensitive smell sensors. Some researchers speculate that the forked nature of the tongue may offer a stereo sense of smell. Crocodilians see well in daylight and may even have color vision; additionally, their vertical, cat-like pupil gives them excellent night vision.

In crocodilians, the upper and lower jaws also are covered with sensory pits, the crocodile version of the lateral line sensory organ found in fish and many amphibians.

These pigmented nodules encase bundles of nerve fibers that respond to the slightest disturbance in surface water, detecting vibrations and small pressure changes in water, making it possible for them to detect prey, danger, and intruders even in total darkness.

While alligators and caimans have the sensory nodules only on their jaws, crocodiles have similar organs on almost every scale on their body. Most reptiles reproduce sexually. This includes many male snakes that rely on scent to find females and that complete fertilization internally. Most reptile species are oviparous egg-laying. Many species of squamates, however, are capable of giving live birth. This is achieved either through ovoviviparity egg retention or viviparity babies born without use of calcified eggs.

Many of the viviparous species feed their fetuses through various forms of placenta, just like mammals Pianka and Vitt They often provide considerable initial care for their hatchlings. Amniotic eggs are covered with leathery or calcareous shells and are compartmentalized by four membranes: Eggs are waterproof, but permeable to gases. Sperm are placed inside the female by internal fertilization prior to the formation of the shell. In addition to the common pattern of sexual reproduction among reptiles, a pattern of asexual reproduction has been identified in six families of lizards and one snake family.

In some species of squamates lizards and snakes , a population of females is able to produce a unisexual diploid clone of the mother.

This asexual reproduction, called parthenogenesis , occurs in several species of gecko and is particularly widespread in the teiids especially Aspidocelis and lacertids Lacerta. Parthenogenetic species are also suspected to occur among chameleons , agamids, xantusiids, and typhlopids.

Reptiles offer economic, ecological, aesthetic, and symbolic value to humans. Some species, such as the green turtle, the iguana, and some snakes, are part of the diet, and the giant Galapagos tortoise was so popular as a food among sailors in the nineteenth century that it was nearly exterminated.

The skins of crocodilians, snakes , and lizards have been used in leather goods, such as shoes, handbags, gloves, and belts, but international agreements protecting endangered species have prompted a shift of reptile skin sources from hunters of wild species to farmers growing reptiles in captivity. Reptiles also are very popular pets.

In the United States , about 3 percent of households have reptiles as pets with many of the reptiles having been imported into the country either legally or illegally as part of the international trade in live exotic animals.

Ecologically , reptiles are a critical element in the food chains of most ecosystems, and sometimes a keystone species whose removal can drastically alter the populations of other organisms.

The consumption by reptiles of rodents and insect pests aids in control of these animals, which can be serious agricultural pests. Aesthetically, many reptiles can be considered beautiful or awe-inspiring, such as the San Francisco garter snake Thamnophis sirtalis tetrataenia , with its bright orange head, black and red stripes, and turquoise belly, and the chameleons with their color changes. Reptiles appear in designs on apparel and other consumer goods because of their appeal.

Symbolically, reptiles appear in literature and religion in a variety of ways. Perhaps the most famous reference is the Bible reference to the serpent in the Garden of Eden, or Jesus advising his disciples to be "wise as serpents. Some reptiles also present threats to people, whether because they are venomous, like some snakes, or can attack humans, such as some crocodilians. In addition, salmonella, a bacterial disease, is sometimes picked up from a reptile's skin when touching a reptile kept as a pet.

Hylonomus, the oldest-known reptile, was about 8 to 12 inches 20 to 30 cm long. Westlothiana, also suggested as the oldest reptile, is for the moment considered to be related more to amphibians than to amniotes.

Other examples of fossil animals considered to be ancient reptiles are those of the genera Petrolacosaurus, Araeoscelis, Paleothyris, Ophiacodontidae, Archaeothyris, and Ophiacodon, and also the family of mesosaurs. The first true "reptiles" or amniotes are categorized as Anapsids Anapsida , which are vertebrates characterized by solid skulls with the conventional openings for nose, eyes, spinal cord, and so forth, but lacking temporal fenestrae jaw muscle attachment sites at holes in the sides of the skull behind the eyes near the temples.

Turtles are believed by some to be surviving anapsids, indeed the only surviving anapsids, as they also share this skull structure. However, this point has become contentious, with some arguing that turtles reverted to this primitive state in the process of improving their armor. Both sides have marshaled evidence, and the conflict has yet to be resolved. Shortly after the appearance in the fossil record of the first reptiles, a second branch appeared.

The original branch led to the Anapsida, which did not develop the jaw muscle attachment holes in their skulls, and the second led to the Diapsida diapsids , which developed two pairs of jaw muscle attachment holes in their skulls behind the eye holes. Diapsids "two arches" are a group of tetrapod animals that appeared in the fossil record about million years ago during the late Carboniferous period.

Living diapsids are extremely diverse, and are considered to include all birds , crocodiles, lizards, snakes, and tuataras and possibly even turtles. While some lost either one hole lizards , or both holes snakes , they are still classified as diapsids based on their assumed ancestry. During the Permian period million years ago , the Diapsida line of descent split into two lineages: The lepidosaurs modern snakes, lizards, and tuataras, as well as, debatably, the extinct sea reptiles of the Mesozoic era and the archosaurs living crocodilians and birds as well as the extinct pterosaurs and dinosaurs.

The earliest solid-skulled amniotes in addition to giving rise to the anapsids, are also considered to have given rise about million years ago to a separate line, the Synapsida synapsids , which have a pair of holes in their skulls behind and above the eyes; this feature has the advantage of lightening the skull and increasing the space for jaw muscles. The synapsids eventually evolved into mammals and the early synapsids have been referred to as mammal-like reptiles by some specialists, while others argue that even the early synapsids were no longer reptiles.

As noted above, from the classical standpoint, reptiles included all the amniotes except birds and mammals. Thus, reptiles were defined as the set of animals that includes crocodiles , alligators , tuatara, lizards , snakes , amphisbaenians , and turtles , grouped together as the class Reptilia Latin repere, "to creep". This is still the usual definition of the term. However, in recent years, many taxonomists have begun to insist that for clear identification of the ancestor-descendant relations of all organisms each defined taxon should be monophyletic, that is, each taxon should include all the descendants from the originating stock.

The reptiles as defined are clearly not monophyletic but rather are paraphyletic , since they exclude both birds and mammals, although these also are considered to be descendant from the original reptile. Colin Tudge writes:.

Mammals are a clade [a monophyletic taxon], and therefore the cladists are happy to acknowledge the traditional taxon Mammalia ; and birds, too, are a clade, universally ascribed to the formal taxon Aves. Mammalia and Aves are, in fact, subclades within the grand clade of the Amniota. But the traditional class Reptilia is not a clade. It is just a section of the clade Amniota: The section that is left after the Mammalia and Aves have been hived off.

It cannot be defined by synamorphies, as is the proper way. It is instead defined by a combination of the features it has and the features it lacks: Reptiles are the amniotes that lack fur or feathers.

Some cladists thus redefine Reptilia as a monophyletic group, including the classic reptiles as well as the birds and perhaps the mammals depending on ideas about their relationships. Others abandon it as a formal taxon altogether, dividing it into several different classes. However, other biologists believe that the common characters of the standard four orders Crocodilia crocodiles , Rhynchocephalia tuataras , Squamata snakes and lizards , and Testudines turtles are more important than the exact relationships, or feel that redefining the Reptilia to include birds and mammals would be a confusing break with tradition.

A number of biologists have adopted a compromise system, marking paraphyletic groups with an asterisk, for example, class Reptilia. Foods with a high calcium: Human nutrient databases can be useful http: Calcium or vitamin D 3 deficiency generally due to poor quality lighting and low-calcium diets leads to secondary nutritional hyperparathyroidism in insectivores and herbivores.

A variety of commercially available foods are available in moist, canned, and dry pellet forms. These may help provide a balanced diet, but they have not been critically evaluated. P ratio of these commonly used items may make them less suitable as a staple component of a reptile diet. Although some species will drink from a water bowl, others will only imbibe water droplets on plants and décor.

Poor water quality has been implicated as a cause of stomatitis in snakes. Lack of appropriate water delivery has been implicated as a predisposing cause of renal disease in green iguanas. The advent of timer-controlled sprinkler systems makes regular water provision possible for many of these more fastidious drinkers. See also Nutrition in Reptiles. The successful diagnosis and treatment of reptile diseases requires proper restraint and performance of a variety of clinical techniques.

Although the principles are similar to those used for domestic animals, there are a number of reptile-specific peculiarities. It may be possible to observe calm specimens unrestrained, permitting an assessment of demeanor, locomotion, and obvious neurologic disorders such as lameness, paralysis, paresis, and head tilt.

Observation of reptiles within their usual environment is particularly valuable and should be done whenever possible. Nervous or aggressive species are best restrained at all times using towels, snake hooks, clear plastic containers, and restraint tubes.

Careful consideration should be given to the safety of veterinary staff, zoo keepers, and private owners when dealing with large or otherwise potentially dangerous reptiles. In many cases, chemical agents can expedite procedures and considerably reduce risks to both the reptile and human handlers. Given the improvements in reptile anesthesia, even manageable reptiles may be preferentially sedated or anesthetized for procedures that would otherwise take longer to accomplish and cause unnecessary stress or discomfort to the animal.

It is possible that sedatives and anesthetics may affect clinical pathologic results, especially hematology. The decision to examine a potentially dangerous reptile should be made with due regard to legislative and safety requirements. No species of Chelonia is legally considered dangerous, but several species eg, snapping turtles, Chelydra spp have a ferocious bite that makes them a formidable opponent.

The risks of reptile-borne zoonoses are probably no greater than for other animal groups, and basic personal hygiene after handling reptile patients will minimize these risks. The major zoonoses include Salmonella , Pseudomonas , Mycobacterium , Cryptosporidium , and Rickettsia spp and pentastomids arachnid lung parasites.

Every reptile must be accurately weighed; an accurate weight is important to avoid deaths associated with drug overdose, particularly anesthetics and aminoglycosides. In addition, serial weight measurements permit an appraisal of growth and captive management, response to treatment, and disease progression or resolution. Relating body weight to length and conformation gives an assessment of body condition. The snout-vent length of lizards and especially snakes is worth noting, because organ position and growth can be calculated as a result.

Chelonian body condition relies on relating total weight to straight carapace length or body volume. Transillumination of the coelom using a cold light source can be used to visualize the internal structures of small lizards and snakes and is particularly useful to confirm suspected impactions and foreign bodies.

Care must be exercised if a hot light source eg, incandescent spotlight is used, because of the possibility of burns. Auscultation of reptiles is difficult and often unrewarding. Electronic stethoscopes with moistened gauze between the shell or scales and the stethoscope diaphragm can be helpful. Doppler ultrasound is particularly useful to determine heart rates.

The head of an aggressive snake or a snake of unknown disposition should be identified and restrained before opening the transportation bag to remove the animal. In general, the head of the snake is held behind the occiput using the thumb and middle finger to support the lateral aspects of the cranium. The index finger is placed on top of the head. The other hand is used to support the body.

When dealing with large boids, a second, third, or even fourth handler is required to support the body during the examination. It is usually safer and more convenient to sedate a large, pugnacious snake than to risk injury to the snake, owner, or staff.

Nonvenomous species should be supported using one or two hands, depending on size. Nervous or aggressive snakes can be restrained using plexiglass tubes or sedated before examination. The clinician should attempt to gauge muscle tone, proprioception, and mobility. Systemically ill serpents will often be limp, lack strength, and be less mobile. Head carriage, body posture, cloacal tone, proprioception, skin pinch, withdrawal, and papillary and righting reflexes can be used to assess neurologic function.

The entire integument, particularly the head and ventral scales, should be thoroughly examined for evidence of dysecdysis poor shedding , trauma, parasitism especially the common snake mite, Ophionyssus natricis , and ticks , and microbiologic infection. Any recently shed skin should also be examined, if available, for evidence of retained spectacles.

The infraorbital pits where present and the nostrils should be free from discharges or retained skin. The eyes should be clear, unless ecdysis is imminent. The spectacles covering the eyes should be smooth; any wrinkles usually indicate the presence of a retained spectacle. The spectacle represents the transparent fused eyelids, and therefore the cornea is not normally exposed. The subspectacular fluid drains through a duct to the cranial roof of the maxilla.

When blocked, the buildup of fluid causes a subspectacular swelling that often becomes infected. Damage to the underlying cornea can result in panophthalmitis and ocular swelling. Retrobulbar abscessation results in protrusion of a normal-sized globe. Other ocular pathologies can include uveitis, corneal lipidosis, and spectacular foreign bodies, including slivers of wood or other vivarium materials.

Working from cranial to caudal, the head and body are palpated for swellings, wounds, and other abnormalities. The position of any internal anomalies, noted as a distance from the snout and interpreted as a percentage of snout-vent length, enables an assessment of possible organ involvement.

Recently fed snakes have a midbody swelling associated with the prey within the stomach; handling such individuals may well lead to regurgitation. Preovulatory follicles, eggs, feces, enlarged organs, and masses may be palpable.

The cloaca can be examined using a dedicated otoscope or by digital palpation. Examination of the oral cavity is often left until last, because many snakes object to such manipulation. However, even before the mouth is opened, the tongue should be seen flicking in and out of the labial notch with regularity. The mouth can be gently opened using a plastic or wooden spatula to permit an assessment of mucous membrane color and the buccal cavity for evidence of mucosal edema, ptyalism, hemorrhage, necrosis, and inspissated exudates.

White deposits may indicate uric acid deposition due to visceral gout. The pharynx and glottis should be examined for hemorrhage, foreign bodies, parasites, and discharges. Open-mouth breathing is a reliable indicator of severe respiratory compromise.

The patency of the internal nares and the state of the polyphyodontic teeth should be noted. Lizards vary considerably in size, strength, and temperament; therefore, a variety of handling techniques are required. The tegus and monitors are renowned for their powerful bites, whereas other species, particularly the green iguana, are much more likely to use their claws and tail. The main problem when handling small lizards is restraining them before they flee.

The lizard should be transported in a securely tied cloth bag, so that the position of the lizard can be identified and the lizard held before the bag is opened. Large lizards are best restrained with the forelimbs held laterally against their coelom and the hindlimbs held laterally against the tail base.

The limbs should never be held over the spine, because fractures and dislocations can occur. Nervous lizards can be wrapped in a towel to aid restraint. Smaller lizards can be restrained around the pectoral girdle, holding the forelimbs against the coelom, although care is required not to impair respiratory movements.

A lizard should never be grasped by the tail, because many species can drop the tail autotomy in an attempt to evade capture. Restricting the vision of a lizard eg, a towel placed over the head is often the simplest way to facilitate handling and examination.

A useful restraint technique for iguanid or monitor lizards uses the vasovagal response: This technique enables the mouth to be gently opened without the need for excessive force. If possible, the lizard should be observed unrestrained to check for neurologic problems. Calm lizards may be permitted to walk around the examination table or on the floor. However, if in any doubt, the lizard should be placed in a large plastic enclosure to prevent escape during observation.

The integument should be examined for parasites essentially mites and ticks and trauma due to fighting, mating, and burns. Lizards tend to shed their skin in stages. Classically, dysecdysis and skin retention occurs around the digits and tail, causing ischemic necrosis. Extensive skin folding and tenting may indicate cachexia and dehydration. The head should be examined for abnormal conformation. The mouth can be opened using a blunt spatula or, in iguanas, by gently applying pressure to the dewlap.

The buccal cavity and glottis should be examined thoroughly for evidence of trauma, infection, neoplasia, and edema, especially pharyngeal edema. The internal extent of any rostral abrasions should be evaluated. The nostrils, eyes, and tympanic scales should be clean and free of discharges.

The presence of dry, white material around the nostrils of some iguanid lizards is normal, because some species excrete salt through specialized nasal glands. The rostrum should be examined for trauma, often caused by repeated attempts to escape from a poorly designed vivarium or to evade cagemates. The head, body, and limbs should be palpated for masses or swellings, which can be abscesses or metabolic bone disorders.

Lizards suffering from severe hypocalcemia and hyperphosphatemia may exhibit periodic tremors and muscle fasciculations. The coelomic body cavity of most lizards can be gently palpated. Food and fecal material within the GI tract, fat bodies, liver, ova, and eggs are usually appreciable.

Cystic calculi, fecoliths, enlarged kidneys, impactions, retained eggs or ova, and unusual coelomic masses may also be noted. The cloaca should be free from fecal staining, with visual and digital examination considered routine. In the green iguana, renomegaly can be appreciated by digital cloacal palpation. The high incidence of dystocia necessitates a need to identify gender during examination.

Many species of lizards are sexually dimorphic, although sexing juveniles can be difficult. Small to medium-sized tortoises are not difficult to handle, although their strength and uncooperative nature can hinder examination. Patiently holding the tortoise with its head down will often persuade a shy individual to protrude the head from the shell.

Placing the thumb and middle finger behind the occipital condyles prevents retraction of the head. However, with larger species, it may be physically impossible to prevent a strong individual from pulling free.

In such cases, sedation or use of a neuromuscular blocking agent may be necessary. The more aggressive aquatic species should be held at the rear of the carapace. Some species eg, snapping turtles have long necks and an extremely powerful bite, necessitating great care.

Examination of the head should include the nostrils for any discharges and the beak for damage and overgrowth. The eyelids should be open and not obviously distended or inflamed, and the eyes should be clear and bright. Conjunctivitis, corneal ulceration, and opacities are frequent presentations. The tympanic scales should be examined for signs of swelling associated with aural abscessation.

Applying steady distractive pressure to the maxilla and mandible can open the mouth, and a mouth gag can be inserted to prevent closure. Aggressive chelonians, generally aquatic species, often threaten by open-mouth displays, which provide a good opportunity to examine the buccal cavity with minimal handling.

Mucus membrane coloration is normally pale; hyperemia may be associated with septicemia or toxemia. Icterus is rare but may occur with biliverdinemia due to severe liver disease. Pale deposits within the oral membranes may represent infection or urate tophi associated with visceral gout.

The glottis is positioned at the back of the fleshy tongue and may be difficult to visualize; however, it is important to check for any inflammation and glottal discharges consistent with respiratory disease.

The integument should be free of damage. Subcutaneous swellings are usually abscesses. Aquatic species appear more susceptible to superficial and deep mycotic dermatitis, especially around the head, neck, and limbs.

The withdrawn limbs can be extended from the shell of small to medium-sized chelonians by applying steady traction. Because the coelomic space within the shell is restricted, gently forcing the hindlimbs into the shell will often lead to partial protrusion of the forelimbs and head, and vice versa. A wedge or mouth gag can be used to prevent complete closure of a hinge. No chelonian will close a hinge on an extended limb. The integument should be examined for parasites particularly ticks and flies , dysecdysis, trauma, and infection that may arise due to predator attacks.

Aggressive conflicts and courting trauma must also be considered in the communal environment. Limb fractures are less common in chelonians than in other reptiles, but when they do occur they are often associated with rough handling and secondary nutritional hyperparathyroidism. Focal subcutaneous swellings are usually abscesses, but grossly swollen joints or limbs are more often cases of fracture, osteomyelitis, or septic arthritis.

The prefemoral fossae should be palpated with the chelonian held head-up. The shell should be examined for hardness, poor conformation, trauma, or infection. Soft, poorly mineralized shells are usually a result of secondary nutritional hyperparathyroidism resulting from dietary deficiencies of calcium, excess phosphorus, or a lack of full-spectrum lighting. Pyramiding of the shell appears to be more associated with inappropriate humidity than dietary imbalances.

Shell infection may present as loosening and softening of the scutes with erythema, petechiae, purulent or caseous discharges, and a foul odor. Prolapses through the vent are obvious, but it is necessary to determine the structure s involved. Prolapses may include cloacal tissue, shell gland, colon, bladder, or phallus. Internal examination using digital palpation and an endoscope is recommended. For some minor procedures eg, blood sampling , simple restraint may be all that is required.

This can be enhanced by temporary immobilization techniques such as dorsal recumbency, reduced light intensity, or gentle ocular pressure vasovagal response. For more invasive and painful procedures, general anesthesia must be used.

Although considerable anatomic, physiologic, and pharmacologic differences exist between reptiles, some general guidelines are applicable. The following is therefore intended as a practical approach, rather than an exhaustive review of reptile anesthesia. All reptiles should be hospitalized and maintained at their preferred optimal temperature zone at all times to minimize physiologic disturbance, facilitate recovery, and maintain immunocompetence.

Although hypothermia will reduce movement, it does not provide analgesia and is therefore unacceptable as a means of anesthesia on welfare grounds. It can also dramatically affect the pharmacokinetics of any drugs administered and greatly prolong recovery.

A full clinical examination should be performed and the animal accurately weighed, although this may not be practical or possible in some cases. The hydration status of all reptiles should be assessed, especially if debilitated or post-hibernation.

For elective procedures eg, neutering , underweight, dehydrated, or debilitated animals should be nursed for days, weeks, or months until their condition improves. For nonelective surgery, dehydration should be corrected before anesthesia. Even the most moribund egg-bound reptile will usually benefit from stabilization for 24—48 hr before surgery is performed. Reptiles that have not been stabilized before surgery tend to succumb intra- or postoperatively.


Intracoelomic fluids are more suitable, but uptake can take many hours and their use is problematic if coeliotomy or coelioscopy is planned. For dehydrated surgical candidates, IV or intraosseous fluid therapy should be administered before, during, and after surgery as necessary. Premedication with sedatives such as acepromazine and atropine is generally rare in reptiles, although midazolam has been advocated in large chelonians.

However, presurgical administration of analgesics should be considered routine see Table: Analgesics, Sedatives, and Anesthetics Used in Reptiles. IV or intraosseous propofol provides a rapid, controlled mode of induction. It is relatively nontoxic, and there is reduced risk of thrombophlebitis if it is injected perivascularly.

This is of particular concern, because IV access may be relatively difficult, especially in active animals undergoing elective procedures.

If IV access is impractical or dangerous to attempt, IM agents can be used to induce sufficient chemical restraint for intubation. For IM injections in lizards and chelonians, the forelimb muscles are preferred, whereas for snakes, the epaxial muscles are used. An IM combination of ketamine , medetomidine or dexmedetomidine , and morphine or hydromorphone has proved effective for a variety of chelonians; this can be readily reversed using atipamezole and, if necessary, naloxone or naltrexone.

Squamates can also be induced by inhalation agents in an induction chamber or by mask. However, breath holding tends to occur in turtles and crocodilians, which can respire anaerobically for prolonged periods.

Induction may take 10—30 min in cooperative lizards and snakes. Intubation of conscious patients has been suggested after local lidocaine spray, but the adverse effects of increased stress and catecholamine release should always be considered. There is also the potential danger of being bitten. Isoflurane or sevoflurane are the agents of choice for maintenance of anesthesia.

These volatile inhalation agents have faster modes of action, are more controllable, and facilitate faster recoveries than most alternatives. Furthermore, their lack of reliance on hepatic metabolism or renal excretion reduces the anesthetic risk to debilitated reptiles or those with questionable renal or hepatic function.

Chelonians red-eared sliders ; less respiratory depression than morphine. Snakes cornsnakes at high doses. Not analgesic for bearded dragons or red-eared sliders. May cause respiratory depression, and high-dose volume may be impractical.

May be able to partially antagonize opiate agonists like morphine. Reversed using atipamezole 0. Premedication, or can be given with ketamine to increase sedative effects or promote similar effects at lower ketamine doses. Often used in combination with ketamine and opiates as a sedative to light anesthetic.

Useful when IV access is difficult. Low dose useful to facilitate intubation. Higher doses associated with prolonged recoveries. Similar effects to those of propofol IV, but higher doses effective IM. Larger IM dose volumes may warrant dividing into two or more injections. Routine gaseous agent; subanesthetic levels provide short-term sedation. Mask down or conscious sedated intubation possible in some species.

Very similar effects to those of isoflurane but recoveries appear to be faster. Preferred agent for critical or large reptiles. Intubation of reptiles is relatively simple. Small-gauge endotracheal tubes or catheters are easily inserted through the glottis immediately caudal to the tongue; this may be aided by forcing the tongue up and forward by pressing a finger into the intermandibular space from under the jaw.

The reptilian glottis is actively dilated, and therefore its movement will often be abolished in anesthetized animals; a guiding stylet can be useful to facilitate endotracheal tube placement. Noncrocodilian reptiles lack a diaphragm; skeletal intercostal muscles Squamata or limb movements Chelonia control breathing. The action of these muscles is abolished at a surgical plane of anesthesia, and intermittent positive-pressure ventilation is required.

Ventilation rates should initially mirror preanesthesia evaluations and then be adjusted to maintain end-tidal capnography readings of 15—25 mmHg. Electrical ventilators enable precise control of ventilation rates and pressures.

Monitoring anesthesia in reptiles differs considerably from doing so in mammals. Palpebral and corneal reflexes are reliable in those species in which they can be elicited ie, all chelonians, all crocodilians, most lizards, but no snakes. However, corneal reflexes are abolished at toxic doses, and pupillary diameter may bear little relation to the depth of anesthesia unless fixed and dilated, which indicates excessive anesthetic depth or brain anoxia and death.

Jaw tone and withdrawal reflexes tongue, limb, or tail are abolished only at a surgical plane of anesthesia. This also correlates with full loss of the righting reflex, loss of spontaneous movement, and complete muscle relaxation. Heart rate may be monitored by auscultation or by visualization or palpation of the heart beat in most snakes and some lizards.

Pulse oximetry, using either an esophageal or cloacal reflectance probe, is useful to monitor pulse rate and strength. Although the blood oxygen saturation SpO 2 readings are often low and have not been validated for reptiles, monitoring the trend in SpO 2 is often helpful. Doppler ultrasonography can also be used over peripheral arteries or the heart. Blood gas estimations are often affected by intracardiac or pulmonary shunts, especially in aquatic species.

However, end-tidal capnography has proved effective. Toward the end of surgery, the anesthetic gas should be discontinued while maintaining ventilation for another 5—10 min to facilitate excretion.

At this point, oxygen should be discontinued in favor of room air delivered by bag-valve mask to encourage spontaneous respiration. Once it is breathing spontaneously, the reptile can be returned to an incubator or vivarium to fully recover. Continued monitoring is essential until righting reflexes return and the animal is ambulatory. Additional analgesia, fluid, and nutritional support should be provided as indicated.

Several anatomic differences make it difficult to obtain quality radiographs in reptiles. The relatively small size of most pet reptiles and the lack of diffuse body fat often produce images of poor contrast. Thick, highly keratinized scales, osteoderms, or shells can severely hinder the x-ray beam, necessitating greater power and a subsequent loss of fine soft-tissue detail. Despite these difficulties, most high-capacity units can be set to produce quality radiographs of reptiles.

Various agents can be used to improve contrast. Water-soluble iodine compounds such as iohexol can be used for GI, urogenital, and IV techniques. The injection of air into the coelom of a lizard can greatly improve the appreciation of preovulatory follicles.

Snakes can be difficult to position and restrain for radiographic examinations unless anesthetized. If the purpose of the examination is simply to exclude radiodense foreign bodies, the snake may be allowed to coil in its natural position.

If detailed examination of the skeletal, respiratory, and digestive system is desired, the snake must be extended. A plastic restraint tube can be used for this purpose; however, this may produce some radiographic artifact. In larger snakes, several films will be needed to radiograph the entire length of the body. Lateral views are best taken using horizontal beams to avoid displacement artifact of the viscera.

However, standard laterals with the snake taped in lateral recumbency can be useful, especially when horizontal beams are not possible or safe to undertake. The interpretation of dorsoventral views are hindered by the spine and ribs but can still be useful when dealing with obvious lesions, including eggs and mineralized masses.

Small lizards can often be restrained by taping them to the radiography film or table for a dorsoventral view. Placing cotton balls over the eyes, and wrapping them with self-adhesive tape will often produce a calm, motionless lizard.

A dorsoventral view can help identify foreign bodies, intestinal impaction, or coelomic masses. A horizontal x-ray beam provides the best lateral imaging in lizards, especially when evaluating the respiratory system. Elevating the body of the lizard on rolled towels or foam pads helps prevent superimposition of the limbs with the coelomic cavity.

The positioning for, and interpretation of, crocodilian radiographs are similar to those used for lizards. Most chelonians are fairly easy to position and restrain. For vertical beam dorsoventral radiographs, most conscious animals will remain motionless long enough to permit exposure.

Ideally, the head and limbs should be extended from the shell to reduce superimposition of the limb musculature on the coelomic viscera.

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