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The Bearded Dragon: An Owner's Guide To A Happy Healthy Pet
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Anatomy and Physiology
Bearded Dragons are four-legged, spine-covered lizards that are more or less disk-or tank-shaped, with a rounded body that lies close to the ground. They appear, ingeneral body shape, more or less similar to the much smaller American Horned Lizards(also known as "horned toads"), although these lizards are not agamidsbut members of the family Iguanaidae. Both however, are well adapted to arid,desert-like conditions and both are found in a variety of dry habitats, ranging fromdesert to plains or scrublands, as well as forested areas. Their sandy colorationand blotchy patterns afford them excellent camouflage against their background. Thosethat live in red, sandy areas develop a reddish-coloration that improves their abilityto conceal themselves.
Bearded Dragons have four robust legs with five clawed toes on each foot. Theclaws are relatively soft and handlers are rarely, if ever, scratched by them. Thefront claws are used to obtain purchase on the tops of such basking objects as fencepoles and tree trunks. The rear toes "dig in" to the objec ts so that thedragon does not fall off.
The female of the species uses her clawed feet to excavate a nest to lay her eggs.Mating behavior and reproduction in wild beardies has been documented by many, includingearly Australian herpetologist Kinghorn as long ago as 1931. More recently, the burrowingbehavior of egg-laying beardies has been described when a Pogona barbata femalewas observed laying her eggs. According to reports, the female digs her nest by scoopingout a hole long enough to bury herself in. She deposits her eggs and then emerges,carefully covering the entrance over before she departs.
All Bearded Dragons have a moderate-size tail that widens greatly toward the base.Unlike most other lizards, they do not practice true caudal autotomy (self-severingof the tail) to escape predators, nor do they have fracture planes in their tailvertebrae that would enable them to do this. They can, however, lose a part of theirtail by having it bitten off, either by another Bearded Dragon or by a predator.If this happens, the remaining tail will heal up.
Spontaneous loss of a beardie's tail might occur between vertebrae as opposedto fracture planes within the bony process itself. Nineteenth-century Australianzoologists wrote that beardies would use their tails in a whipping motion to defendthemselves. However, it is likely that this belief is not highly accurate. Beardiesare not known to actively strike human handlers with their tails (at least mine neverhave). If tail whipping were a common defense, one would expect to see it used whenhandled.
Like most reptiles, Bearded Dragons have three- chambered hearts. Their anatomyalso ena bles them to change the pattern of blood flow within the head and body tohelp them control their temperature. When they first emerge into the daylight inthe morning, they divert blood to large sinuses in the head. This heats up the dragon'sbrain and sensory organs first, paving the way to maximum functioning early in theday. When they bask, back facing the sun, their dorsal blood vessels dilate and theirheart rate increases, which also helps speed up transfer of heat throughout the body.
The digestive system of Bearded Dragons begins with the oral cavity and teeth.Unlike many herbivorous reptiles, beardies chew their food using their teeth, releasingnutrients from within, thereby aiding in the digestion of vegetable matter. Foodis swallowed and transmitted to the stomach via a relatively short esophagus.
In the stomach and the intestines that follow, the food is more thoroughly digestedand is subject to microbial degradation or fermentation, a specialized type of digestionemployed by animals that consume significant amounts of vegetable matter, includingthose that do so exclusively. Unlike herbivorous mammals (for example, horses, cowsand rabbits), reptiles do not suckle or maintain close contact with their young followingbirth. Accordingly, newborn Bearded Dragons must obtain the bacteria necessary tohelp ferment and digest their food by ingesting fecally contaminated bits of soil.In captivity, therefore, newborn dragons should be started on a diet of small insects(pinhead crickets or fruit flies) until they have built up sufficient numbers ofthis kind of bacteria in order to obtain nutritional benefit from a vegetarian diet.
Bearded Dragons are indiscr iminate feeders of vegetable matter and will eat leavesand fruits as well as bits of whole raw vegetable matter such as carrots. You candemonstrate the unique way Bearded Dragons chew their food by offering them a babycarrot or small piece of a larger carrot and watch them chew and pulverize it forswallowing and digestion. Beardies also eat flowers, such as yellow dandelions, andseem attracted to bright colors when feeding.
The intestinal tract terminates in an all-purpose cavity known as the cloaca.It terminates with an anal portal through which excrement or waste products are dischargedto the environment. The cloaca is used not only for storage and ejection of fecaland urinary waste, but also for sexual intercourse and passage of eggs in reproduction.
The reproductive system of beardies is similar to that of all other lizards. Itconsists of paired, internally suspended gonads (ovaries in females, testes in males).Female ovaries communicate with the cloaca via oviducts, testes with a specializedintromittent organ known as a hemipenes, which is located inside the cloaca but whichcan be averted outward to accomplish true, internal fertilization of the female'seggs during mating.
Urinary wastes are processed by paired kidneys and empty into the cloaca for excretionby the ureters. As discussed earlier, beardies often go for long periods of timewithout water and often obtain what little water they can from their food. Thus,they must be able to conserve fluids. In order to rid themselves of urinary wasteswhile maintaining fluids, beardies and other reptiles with a similar problem excretea "dry" urine, which appears as a chalky, white powdery su bstance consistinglargely of the nitrogenous waste product known as uric acid. Whereas ammonia andurea are soluble in water, uric acid is not. When the liquid urine enters the bladderor the cloaca, water is reabsorbed. This process in reptiles permits the excretionof nitrogenous waste products with little or no fluid wasted in the process. Thismaterial, along with fecal wastes, is emptied to the outside via the cloaca.
The skin of Bearded Dragons is rough, warty or leathery. It contains many soft"spines" that make them somewhat unpalatable to larger predators. Theirskin bumps are useful in obtaining water, living as they do in areas where rain orstanding fresh water is scarce to nonexistent. When rain does occur, it washes throughthe dragon's scales and pours down onto its snout. Dragons have been observed standingin the rain, their bodies widely spread and pointed toward the rainfall. They lowertheir heads below body level and as the rain runs onto their snout they lick it offor catch it with their tongues. When water is not available, they conserve what theyhave by producing a concentrated semisolid urine, reabsorbing the watery part intotheir bodies. Note: As a desert species, they survive well in the absenceof rainfall or drinking water, but captives should be sprayed lightly several timesa week. Beardies also obtain water from their food, and their vegetable meals canbe easily sprayed down with water to aid in this purpose (see chapter 8 for moreinformation on providing food and water for your beardies).
The rough skin of Bearded Dragons has many soft "spines" that diminishtheir appeal to predators.
Bearded Dr agons have Jacobson's organs in the roofs of their mouths. This organ,also found in snakes as well as in other lizards, functions like a cross betweenthe senses of taste and smell. Unlike snakes and Monitor Lizards, however, beardiesrarely use tongue flicking to check out the palatability or suitability of a plantor bug as a food item. They seem to rely almost entirely on their visual senses inthis regard (because snakes have very poor vision, they depend on the chemical cluesthey pick up by tongue flicking). Beardies' eyes are mounted laterally on the sidesof their head, thereby providing them little or no binocular vision; yet they candetect food, enemies or mates at distances of 100 feet. There are apparently no detailedstudies concerning their ability to see colors. I have observed, however, that theycan evidently discern certain colors and select items of food based on their coloration.In particular, they appear to see reds and yellows well, the colors of flowers thatare a favorite food. Experiments performed on captive beardies indicate that theyhave excellent hearing; standing alert at loud or unusual noises. When they holdtheir bodies close to the ground, they can also detect ground vibrations, a sensethat gives them warning of large predators in the vicinity. Nonetheless, this abilitydoes not seem to extend to pavement--when absorbing heat from roadways, a significantpercentage of beardies get run over.
By holding their bodies close to the ground, beardies sense lurking predators.
Although beardies resemble horned lizards in their body shape, it is their differencein dentition that sets them apart. Iguanids have their teeth set in small indentationson the inner sides of their jaw bones, an arrangement referred to as pleurodonty.Agamids, on the other hand, have all but their front teeth fused to the sides oftheir jaws, a condition known as acrodonty. The teeth of pleurodont iguanids fallout and grow back in at regular intervals, whereas agamids replace only their front,pleuordont teeth.
The two kinds of teeth seen in beardies and other agamids accommodate the widediversity of their diets. The replaceable, pleurodont teeth are cone-shaped or pointed,whereas the more rearward permanent or acrodont teeth are compressed or chisel-shaped.The front teeth are useful for grasping and piercing, while the rear teeth are bettersuited to cutting and slicing, being especially adept at manipulating plant matter.