Lizards

Unlike snakes , most lizards (with the exception of some legless forms) have more or less developed extremities . Although legless lizards look like snakes in appearance, they still have a sternum , and in most - the limb girdles; unlike snakes, the left and right halves of the jaw apparatus are motionlessly spliced. A characteristic feature of the suborder is also incomplete ossification of the anterior part of the brain box and no more than two sacral vertebrae . ^[3] In legless lizards, the eyes, as a rule, are equipped with movable separate eyelids, while in snakes the eyelids have grown together, forming transparent “lenses” on the eyes. They also differ in a number of other features, such as, for example, the structure and structure of the scales .

Circulatory system

The heart of the lizards is three-chambered, has two atria and one ventricle, divided into three parts: venous cavity, arterial cavity and pulmonary cavity. Oxygen-poor blood enters the venous cavity from the right atrium, and oxygen-rich blood from the left atrium enters the arterial cavity. Blood leaves the heart through the pulmonary artery originating in the pulmonary cavity and two aortic arcs extending from the venous cavity. The paired left and right arches of the aorta merge behind the heart into the dorsal aorta. All three cavities of the heart of the lizards communicate, but a muscle flap and a two-phase contraction of the ventricle minimize blood mixing (bypass) during normal activity. Poor oxygen blood flows from the venous cavity to the pulmonary; the atrioventricular valve prevents it from mixing with oxygen-rich blood from the arterial cavity. Then the contraction of the ventricle pushes this blood from the pulmonary cavity into the pulmonary artery. The atrioventricular valve then closes, allowing oxygen-rich blood from the arterial cavity to enter the venous and leave the heart through the aortic arches. Thus, the three-chamber heart of lizards is functionally similar to the four-chamber. Lizards also have a developed separation of pulmonary and systemic blood pressure. Nevertheless, controlled shunting is possible and plays a physiological role in some cases, for example, with prolonged immersion in aquatic species.

Respiratory system

Herbivorous species, such as the green iguana, have nasal salt glands. When the osmotic pressure of blood plasma rises, excess sodium and potassium is removed through these glands. This mechanism allows you to save water and should not be confused with diseases of the respiratory system.

In primitive lizards, the lungs are bags, divided into faveols having a spongy structure. In more developed species, the lungs are divided into septa that are interconnected. The lungs of the monitor lizards are multi-chamber, with bronchioles, each of which ends in a faveola. In chameleons, outgrowths of the lungs form bags located at the edges of the body, which do not take part in gas exchange, but serve to increase the body, for example, when repelling predators. Some chameleons have an extra lung lobe located in front of their forelimbs. In infectious processes, it can be filled with exudate and cause swelling of the neck.

Vocal cords are usually present and can be well developed, for example, in some geckos that can make loud sounds.

Lizards have no diaphragm and breathing occurs through the movement of the chest. The lizards and puffers have an incomplete septum, which separates the abdominal cavity from the chest cavity, but does not participate in breathing. The glottis is usually closed, except for periods of inhalation and exhalation. Swelling of the throat does not lead to increased breathing, but is an auxiliary process in the sense of smell. Lizards often inflate their lungs to the maximum to appear larger in times of danger.

Some species are capable of anaerobic respiration during the absence or delay of normal.

Digestive system

The lips of the lizards are formed by flexible skin, but still motionless. The teeth are most often pleurodontic (attached on the sides of the jaws without pockets), in agamas and chameleons - acrodontic (attached to the chewing edge of the jaws without pockets). Pleurodont teeth are replaced throughout life. Acrodontic teeth are replaced only in very young individuals, although new teeth may be added to the posterior margin of the jaw with age. Some agamas have several fang-like pleurodont teeth on the front of the jaw along with normal acrodont teeth. Care must be taken not to damage irreparable acrodontic teeth when opening the mouth of agamas and chameleons. Diseases of the periodontium (tissue surrounding the teeth) are observed in species with acrodont teeth. The teeth of lizards are usually adapted to capture, tear or grind food, and for lizards - to cut it.

Poisonous lizards are many species from the Toxicofera group , including many iguanoids and monitor lizards. However, only venomotorians actually use poison when hunting or self-defense: vests ( Heloderma suspectum ) and escortion ( Heloderma horridum ). Their teeth have gutters that are anatomically unconnected with the poisonous glands that are located under the tongue. The poison flows down the gutters of the teeth and penetrates the victim’s skin during a bite. Symptoms of poisoning include pain, low blood pressure, palpitations, nausea, and vomiting. The antidote does not exist.

The language of lizards differs in shape and size in different species. Most often, it is mobile and easily pulled out of the oral cavity. Taste tubercles are developed in lizards with a soft tongue and are absent in species whose tongue is covered with keratin, for example, in monitor lizards. Taste tubercles are also in the throat. Lizards with a strongly bifurcated tongue (monitor lizards and tegu) push it to deliver odorous molecules to the vomeronasal (Jacobson) sense of smell. The tongue plays an important role in the extraction of food from chameleons. At green iguanas, the tip of the tongue is bright red. This is not a sign of pathology. Paired Jacobson organs open with small holes in the anterior inner part of the upper jaw, and immediately behind them are the internal nostrils.

The stomach of lizards is simple, J-shaped. Digestion of stones for digestion is not normal.

The cecum is present in many species. The large intestine has thin walls and fewer muscle fibers than the stomach and small intestine.

Many herbivorous species have a colon, divided into chambers for more complete fermentation of food masses. Such species are characterized by a relatively high optimal ambient temperature, which is necessary to maintain microbial activity. The green iguana also belongs to such lizards.

The cesspool is divided into three parts: coprodeum, urodeum and proctodeum. The anus in the lizards is transverse.

Genitourinary system

The lizard buds are metanephric and are located in the back of the body cavity or in the depth of the pelvic canal, depending on the species. As a result, kidney enlargement for some reason can lead to obstruction of the colon, which passes exactly between them.

The rear end of the kidneys of some geckos, skinks, and iguanas varies by gender. This area is called the genital segment. During the mating season, this part of the kidney increases in size and promotes the production of seminal fluid. The color of the genital segment may also vary.

Nitrogen-containing metabolic waste products are removed from the body in the form of uric acid, urea or ammonia. Reptile buds consist of a relatively small number of nephrons, do not have a pelvis and loops of Henle and are not able to concentrate urine. However, water can be absorbed back from the bladder, resulting in the release of concentrated urine. The release of urea and ammonia is accompanied by significant water losses, therefore, waste is removed only from aquatic and semi-aquatic species. Desert species secrete insoluble uric acid.

Almost all lizards have a thin-walled bladder. In cases. When not present, urine builds up in the back of the colon. Since urine flows from the kidneys through the urethra to the cloaca before it enters the bladder (or colon), it is not sterile, like in mammals. The composition of urine can change inside the bladder, so the results of its analysis do not so reliably reflect kidney function. Like mammals. Bladder stones can form as a result of excessive loss of water or a protein-rich diet. Stones are usually single, with smooth edges, layered and large.

The mating season is determined by the length of daylight hours, temperature, humidity and food availability. In males, depending on the sexual season, the testes can significantly increase. Males of green iguanas during the mating season become more aggressive.

Fertilization is internal. Male lizards have paired hemipenis, in which there is no cavernous tissue. At rest, they are in a screwed position at the base of the tail and can form noticeable tubercles. Hemipenis is used only for reproduction and does not participate in urination.

Female lizards have paired ovaries and oviducts that open into the cloaca. Clutch delay can be preovulatory when ovulation does not occur and mature follicles remain in the ovaries, and postovulatory when the eggs are delayed in the oviducts.

Sex determination in young individuals is difficult; in most adults, sexual dimorphism is observed. Adult male iguanas have large dorsal ridges, chests, and hemipenis tubercles at the base of the tail. Male chameleons often have pronounced ornaments on their heads in the form of horns or ridges. Males of other lizards often have large heads, bodies, and bright colors.

The femoral and precloacal pores of males are larger than those of females. This is perhaps the most reliable means of determining the sex of adult lizards. Sex tests can be used with iguanas and monitor lizards, but with less certainty than snakes. The introduction of saline into the base of the tail for eversion of the hemipenis should be done with great care so as not to injure the hemipenis. A common complication is necrosis. This method is mainly used in species whose sex determination is difficult by other methods - the tag, large skinks and venomous teeth. Hemipenises can be turned out in males under anesthesia by pressing on the base of the tail immediately after the cesspool. Hemipenis of many monitor lizards is calcified and can be distinguished on x-rays. To determine the sex, an enoscopy can be done to examine the gonads. Ultrasound can detect the gonads in the body cavity or the presence or absence of hemipenis at the base of the tail.

Lizards can be oviparous, ovoviviparous (when the eggs remain in the body of the female until birth), viviparous (with a placental type or circulatory connection) and multiply by parthenogenesis. Some populations of the species of the family of true lizards (a number of species from the genus Lacerta ) and runner lizards ( Сnemidophorus ) consist only of female individuals breeding by parthenogenesis.

Nervous system

The brain of non-avian reptiles is more developed than that of amphibians and fish, although it is small in size - no more than 1% of body weight. There are 12 pairs of cranial nerves. The difference between the vertebral column of reptiles and mammals is that in the first, the spinal cord continues right up to the tip of the tail.

Sense organs

Ear

The ear performs the functions of hearing and maintaining balance. The tympanic membrane is usually visible inside small depressions on the sides of the head. It is covered with skin, the top layer of which changes during molting. In some species, for example, in the ankleless lizard (Holbrookia maculata), the tympanic membrane is covered with scaly skin and is not visible. Reptiles have only two auditory bones: the stapes and its cartilaginous process. Eustachian tubes connect the middle ear cavity and pharynx.

Eyes

The structure of the eye of reptiles is similar to that of other vertebrates. The iris contains striated, rather than smooth, muscle fibers, so regular mydriatics have no effect.

The pupil is usually round and relatively motionless in daytime species and has the appearance of a vertical gap in nighttime. The pupil of many geckos has jagged edges, which is noticeable when it is completely narrowed. The image of them is repeatedly superimposed on the retina, which allows geckos to see even in very low light. The lens does not move, its shape changes under the influence of muscle fibers of the ciliary body.

The pupillary reflex is absent. There is no descemet membrane in the cornea.

The eyelids are usually present, except for some geckos and skinks of the genus Albepharus , whose eyelids are fused and transparent, like snakes. The lower eyelid is more mobile, and it closes the eye if necessary. In some lizards, it can be transparent, which allows them to see, while providing eye protection. Blinking membrane is usually present.

The retina is relatively avascular, but contains the papillary body - a large plexus of blood vessels that falls into the vitreous.

The well-developed “third eye” in some species is located on the top of the head. This is the eye in which there is a retina and lens, and which is connected by nerves to the pituitary gland. This organ plays a role in hormone production, thermoregulation and does not form images.

Musculoskeletal system

Many lizards are capable of autotomy - dropping the tail. The tail is often colored brightly to attract the attention of a predator to it. Such lizards have vertical fault planes of cartilage or connective tissue in the body and part of the nerve arches in the caudal vertebrae. In iguanas, this tissue ossifies with age, and the tail becomes stronger. The tail that has grown again has a usually darker color, a changed pattern of scales and shape.

Ribs are usually found on all vertebrae except the caudal.

Endocrine system

The level of sex hormones is determined by the length of daylight hours, temperature, and seasonal cycles.

The thyroid gland, depending on the species, can be single, bilobate or paired and is responsible for molting. Paired parathyroid glands control the level of calcium and phosphorus in the blood plasma.

The adrenal glands are located in the ligament of the testis and should not be removed in place with it during castration.

The pancreas of reptiles performs exocrine and endocrine functions. Beta cells produce insulin, but diabetes is rare in lizards and is usually associated with some other systemic disease. Insulin and glucagon control plasma sugar levels.

Most lizards are carnivores . Small and medium-sized species feed mainly on various invertebrates: insects , arachnids , mollusks , and worms . Large, truly predatory lizards ( monitor lizards , tegu ) attack small vertebrates: other lizards, frogs , snakes, small mammals and birds , and also eat eggs of birds and reptiles. The largest modern lizard, the Komodo lizard ( Varanus komodoensis ), attacks large animals such as deer , wild pigs, and Asian buffalo . Some carnivorous species of lizards are stenophages , that is, they specialize in eating any particular type of food. For example, moloch ( Moloch horridus ) feeds only on ants , and the pink-speaking skink ( Hemisphaeriodon gerrardii ) in nature eats exclusively terrestrial mollusks.

Some large iguanas , agamas, and skink lizards are fully or almost completely herbivorous. Such species eat fruits , leaves , young shoots and flowers of plants . However, in some species, young animals can eat insects, as they grow older, they switch to plant food.

Among the lizards there are many omnivorous species that use both animal and plant foods (for example, gigantic skinks , many agamas). Madagascar daytime geckos , in addition to insects, willingly eat nectar and pollen of flowers and pulp of juicy ripe fruit . Even among the lizards, the overwhelming majority of whom are predators, there are exceptions - the smaragd lizard and Gray lizard can eat fruits.

Fossils

According to one version, the oldest discovered fossil lizard specimen is the representative of the group Iguania Tikiguania estesi , found in India in layers dating from the Triassic period (age about 220 million years) ^[4] . But the similarity between Tikiguania and modern agamas raised doubts about her age. As an alternative hypothesis, it was suggested that these remains belong to the late Tertiary or even Quaternary period, and they appeared in the Triassic rocks due to the mixing of these rocks with newer ones ^[5] .

In the suborder of lizards there are 6 infraorders with 37 families ^[6] :

• Infraorder Iguania - Iguanaceae
  1. Family Agamidae - Agamidae
  2. Chamaeleonidae Family - Chameleons
  3. Family corytophanidae
  4. Crotaphytidae Family - Collared Iguanas
  5. Dactyloidae Family
  6. Hoplocercidae Family
  7. Family Iguanidae - Iguanas
  8. Leiocephalidae Family - Masked Iguanas
  9. Leiosauridae family
  10. Family Liolaemidae
  11. Opluridae Family
  12. Family Phrynosomatidae
  13. Polychrotidae Family - Anolis
  14. Tropiduridae Family
• Gekkota Infraorder - Gecko - shaped
  • Gekkonidae Family - Gecko
  • Carphodactylidae family
  • Family Diplodactylidae
  • Eublepharidae Family - Eublepharic
  • Family Phyllodactylidae
  • Sphaerodactylidae Family
  • Family Pygopodidae - Scales
• Infraorder Scincomorpha - Skink - shaped
  • Cordylidae Family - Belt Tails
  • Gerrhosauridae Family - Herrosaurs
  • Gymnophthalmidae Family
  • Family Teiidae - Theiids
  • Lacertidae Family - Real Lizards
  • Scincidae Family - Skink
  • Xantusiidae Family - Night Lizards
• Infraorder Diploglossa - Spindle - shaped
  • Family Anguidae - Spindle
  • Anniellidae Family - Legless Lizards
  • Xenosauridae Family - Xenosaurs
• Dibamia Infrastructure Squad
  • Dibamidae Family - Worm - shaped Lizards
• Infraorder Varanoidea - Lenticular (= Platynota )
  • Helodermatidae Family - Marmot
  • Lanthanotidae Family - Earless Monitor Lizards
  • Varanidae Family - Varanas
  • † Mosasauridae Family - Mozasaurs
• Superfamily Shinisauroidea
  • Shinisauridae Family

• In Western European art, the lizard was an attribute of personified Logic (as one of the Seven Free Arts ) ^[7] .
• She was also chosen as his emblem by the Mantua Duke Federico II Gonzaga . The image accompanied the motto Quod huic deest me torquet ("I am oppressed by what she lacks"), hinting at the subject of his passion ^[7] .
• See also salamander .
• In Russian literature, the lizard - the Mistress of the Copper Mountain - is one of the main characters in Bazhov's tales.

• List of Russian Lizards
• List of lizards of Ukraine
• List of Kazakhstan Lizards

• Shimkevich V.M. ,. Lizards // Brockhaus and Efron Encyclopedic Dictionary : in 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.
• Lizards // Small Encyclopedic Dictionary of Brockhaus and Efron : in 4 volumes - St. Petersburg. 1907-1909.
• Lizards // Great Soviet Encyclopedia : [in 30 vol.] / Ch. ed. A.M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.
• Lizards - an article from the encyclopedia "Around the World"
• Lizards // Collier Encyclopedia
• Melissa Kaplan - Reptile Skin Basics Construction, Infections, and Color - Website
• Lizards at Bushy Park Wetlands - Website
• Australian Museum Online - Frequently asked questions - Reptiles