82-451: Sauria Macartney , 1802 Lizard is the common name used for all squamate reptiles other than snakes (and to a lesser extent amphisbaenians ), encompassing over 7,000 species , ranging across all continents except Antarctica , as well as most oceanic island chains . The grouping is paraphyletic as some lizards are more closely related to snakes than they are to other lizards. Lizards range in size from chameleons and geckos
164-635: A chemical electronic bond ; they are comparatively weak and therefore more susceptible to disturbance. The van der Waals force quickly vanishes at longer distances between interacting molecules. Named after Dutch physicist Johannes Diderik van der Waals , the van der Waals force plays a fundamental role in fields as diverse as supramolecular chemistry , structural biology , polymer science , nanotechnology , surface science , and condensed matter physics . It also underlies many properties of organic compounds and molecular solids , including their solubility in polar and non-polar media. If no other force
246-487: A branch and stays perfectly still, with only its eyes moving. When an insect lands, the chameleon focuses its eyes on the target and slowly moves toward it before projecting its long sticky tongue which, when hauled back, brings the attached prey with it. Geckos feed on crickets , beetles, termites and moths . Termites are an important part of the diets of some species of Autarchoglossa, since, as social insects , they can be found in large numbers in one spot. Ants may form
328-420: A doubled clitoris. The majority of species are oviparous (egg laying). The female deposits the eggs in a protective structure like a nest or crevice or simply on the ground. Depending on the species, clutch size can vary from 4–5 percent of the females body weight to 40–50 percent and clutches range from one or a few large eggs to dozens of small ones. In most lizards, the eggs have leathery shells to allow for
410-579: A few centimeters long to the 3-meter-long Komodo dragon . Most lizards are quadrupedal, running with a strong side-to-side motion. Some lineages (known as " legless lizards ") have secondarily lost their legs, and have long snake-like bodies. Some lizards, such as the forest-dwelling Draco , are able to glide. They are often territorial , the males fighting off other males and signalling, often with bright colours, to attract mates and to intimidate rivals. Lizards are mainly carnivorous, often being sit-and-wait predators ; many smaller species eat insects, while
492-416: A function of separation since the force on an object is the negative of the derivative of the potential energy function, F V d W ( z ) = − d d z U ( z ) {\displaystyle \ F_{\rm {VdW}}(z)=-{\frac {d}{dz}}U(z)} . This yields: In the limit of close-approach, the spheres are sufficiently large compared to
574-451: A greater total area of contact between two particles or between a particle and a wall, this increases the van der Waals force of attraction as well as the tendency for mechanical interlocking. The microscopic theory assumes pairwise additivity. It neglects many-body interactions and retardation . A more rigorous approach accounting for these effects, called the " macroscopic theory ", was developed by Lifshitz in 1956. Langbein derived
656-558: A limited ability to regulate their body temperature, and must seek out and bask in sunlight to gain enough heat to become fully active. Thermoregulation behavior can be beneficial in the short term for lizards as it allows the ability to buffer environmental variation and endure climate warming. In high altitudes, the Podarcis hispaniscus responds to higher temperature with a darker dorsal coloration to prevent UV-radiation and background matching. Their thermoregulatory mechanisms also allow
738-551: A much more cumbersome "exact" expression in 1970 for spherical bodies within the framework of the Lifshitz theory while a simpler macroscopic model approximation had been made by Derjaguin as early as 1934. Expressions for the van der Waals forces for many different geometries using the Lifshitz theory have likewise been published. The ability of geckos – which can hang on a glass surface using only one toe – to climb on sheer surfaces has been for many years mainly attributed to
820-570: A pouch beneath its eyes, to a distance of about two metres (6.6 feet); the blood tastes foul to these attackers. The closest living relatives of lizards are rhynchocephalians , a once diverse order of reptiles, of which is there is now only one living species, the tuatara of New Zealand. Some reptiles from the Early and Middle Triassic , like Sophineta and Megachirella , are suggested to be stem-group squamates, more closely related to modern lizards than rhynchocephalians, however, their position
902-656: A practical anatomist with great experience in teaching, he had much to do in shaping the Anatomy Act of 1832 . He also wrote numerous papers in the Philosophical Transaction and his articles on comparative anatomy are published in Abraham Rees's Cyclopædia London, 1802–1819. These were: Macartney noted in his diary that he was now engaged as a regular contributor at a higher rate than any other because at that time no other person understood
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#1732775876211984-463: A predator that has caught them; attempt to outrun the rattlesnake , which does not pursue prey; but stay still, relying on their cryptic coloration, for Masticophis whip snakes which can catch even swift prey. If caught, some species such as the greater short-horned lizard puff themselves up, making their bodies hard for a narrow-mouthed predator like a whip snake to swallow. Finally, horned lizards can squirt blood at cat and dog predators from
1066-427: A prominent part of the diet of some lizards, particularly among the lacertas. Horned lizards are also well known for specializing on ants. Due to their small size and indigestible chitin , ants must be consumed in large amounts, and ant-eating lizards have larger stomachs than even herbivorous ones. Species of skink and alligator lizards eat snails and their power jaws and molar-like teeth are adapted for breaking
1148-597: A pupil in the college school, Mercer Street, Dublin, where he made some dissections for the museum, and he attended the Lock hospital and the Dublin dispensary. In 1796 he came to London to attend the Hunterian or Great Windmill Street school of medicine, and he became an occasional pupil at St. Thomas's and Guy's hospitals. He also attended the lectures of John Abernethy at St. Bartholomew's Hospital , and through his influence
1230-476: A single clade , the Toxicofera ). However, most of these putative venom genes were "housekeeping genes" found in all cells and tissues, including skin and cloacal scent glands. The genes in question may thus be evolutionary precursors of venom genes. Recent studies (2013 and 2014) on the lung anatomy of the savannah monitor and green iguana found them to have a unidirectional airflow system, which involves
1312-697: A species affects the structure of territories, for example, rock lizards have territories atop rocky outcrops. Some species may aggregate in groups, enhancing vigilance and lessening the risk of predation for individuals, particularly for juveniles. Agonistic behaviour typically occurs between sexually mature males over territory or mates and may involve displays, posturing, chasing, grappling and biting. Lizards signal both to attract mates and to intimidate rivals. Visual displays include body postures and inflation, push-ups, bright colours, mouth gapings and tail waggings. Male anoles and iguanas have dewlaps or skin flaps which come in various sizes, colours and patterns and
1394-415: A transient shift in electron density . Specifically, the electron density may temporarily shift to be greater on one side of the nucleus. This shift generates a transient charge which a nearby atom can be attracted to or repelled by. The force is repulsive at very short distances, reaches zero at an equilibrium distance characteristic for each atom, or molecule, and becomes attractive for distances larger than
1476-422: A variety of different camouflage methods . Many lizards are disruptively patterned . In some species, such as Aegean wall lizards , individuals vary in colour, and select rocks which best match their own colour to minimise the risk of being detected by predators. The Moorish gecko is able to change colour for camouflage: when a light-coloured gecko is placed on a dark surface, it darkens within an hour to match
1558-402: Is a measure of the dispersive interaction. For macroscopic bodies with known volumes and numbers of atoms or molecules per unit volume, the total van der Waals force is often computed based on the "microscopic theory" as the sum over all interacting pairs. It is necessary to integrate over the total volume of the object, which makes the calculation dependent on the objects' shapes. For example,
1640-506: Is based on genomic analysis by Wiens and colleagues in 2012 and 2016. Excluded taxa are shown in upper case on the cladogram. Dibamidae Diplodactylidae [REDACTED] James Macartney (anatomist) James Macartney (born 8 March 1770 in Armagh , died 6 March 1843 in Dublin ) was an Irish anatomist . He began life as an Irish volunteer in 1780, and was afterwards educated at
1722-644: Is disputed, with some studies recovering them as less closely related to squamates than rhynchocephalians are. The oldest undisputed lizards date to the Middle Jurassic, from remains found In Europe, Asia and North Africa. Lizard morphological and ecological diversity substantially increased over the course of the Cretaceous . In the Palaeogene , lizard body sizes in North America peaked during
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#17327758762111804-663: Is known to occur in various species of whiptail lizards . Parthenogenesis was also recorded in species that normally reproduce sexually. A captive female Komodo dragon produced a clutch of eggs, despite being separated from males for over two years. Sex determination in lizards can be temperature-dependent . The temperature of the eggs' micro-environment can determine the sex of the hatched young: low temperature incubation produces more females while higher temperatures produce more males. However, some lizards have sex chromosomes and both male heterogamety (XY and XXY) and female heterogamety (ZW) occur. A significant component of aging in
1886-465: Is often used as an approximate model for the isotropic part of a total (repulsion plus attraction) van der Waals force as a function of distance. Van der Waals forces are responsible for certain cases of pressure broadening ( van der Waals broadening ) of spectral lines and the formation of van der Waals molecules . The London–van der Waals forces are related to the Casimir effect for dielectric media,
1968-534: Is present, the distance between atoms at which the force becomes repulsive rather than attractive as the atoms approach one another is called the van der Waals contact distance ; this phenomenon results from the mutual repulsion between the atoms' electron clouds . The van der Waals forces are usually described as a combination of the London dispersion forces between "instantaneously induced dipoles ", Debye forces between permanent dipoles and induced dipoles, and
2050-461: Is proportional to the polarizability of the molecule, which in turn depends on the total number of electrons and the area over which they are spread. Hydrocarbons display small dispersive contributions, the presence of heteroatoms lead to increased LD forces as function of their polarizability, e.g. in the sequence RI>RBr>RCl>RF. In absence of solvents weakly polarizable hydrocarbons form crystals due to dispersive forces; their sublimation heat
2132-511: The Keesom force between permanent molecular dipoles whose rotational orientations are dynamically averaged over time. Van der Waals forces include attraction and repulsions between atoms , molecules , as well as other intermolecular forces . They differ from covalent and ionic bonding in that they are caused by correlations in the fluctuating polarizations of nearby particles (a consequence of quantum dynamics ). The force results from
2214-405: The common basilisk , can run across water. Lizards make use of their senses of sight , touch , olfaction and hearing like other vertebrates . The balance of these varies with the habitat of different species; for instance, skinks that live largely covered by loose soil rely heavily on olfaction and touch, while geckos depend largely on acute vision for their ability to hunt and to evaluate
2296-589: The geckos , anoles , and chameleons , have modified the scales under their toes to form adhesive pads , highly prominent in the first two groups. The pads are composed of millions of tiny setae (hair-like structures) which fit closely to the substrate to adhere using van der Waals forces ; no liquid adhesive is needed. In addition, the toes of chameleons are divided into two opposed groups on each foot ( zygodactyly ), enabling them to perch on branches as birds do. Aside from legless lizards , most lizards are quadrupedal and move using gaits with alternating movement of
2378-483: The microflora necessary for their transition to a plant-based diet. Perhaps the most herbivorous species is the marine iguana which dives 15 m (49 ft) to forage for algae , kelp and other marine plants. Some non-herbivorous species supplement their insect diet with fruit, which is easily digested. Lizards have a variety of antipredator adaptations , including running and climbing, venom , camouflage , tail autotomy , and reflex bleeding . Lizards exploit
2460-656: The Komodo dragon can kill prey as large as water buffalo . Dragons are prolific scavengers , and a single decaying carcass can attract several from 2 km (1.2 mi) away. A 50 kg (110 lb) dragon is capable of consuming a 31 kg (68 lb) carcass in 17 minutes. Around 2 percent of lizard species, including many iguanids, are herbivores. Adults of these species eat plant parts like flowers, leaves, stems and fruit, while juveniles eat more insects. Plant parts can be hard to digest, and, as they get closer to adulthood, juvenile iguanas eat faeces from adults to acquire
2542-431: The Komodo eats mammals as big as water buffalo . Lizards make use of a variety of antipredator adaptations , including venom , camouflage , reflex bleeding , and the ability to sacrifice and regrow their tails . The adult length of species within the suborder ranges from a few centimeters for chameleons such as Brookesia micra and geckos such as Sphaerodactylus ariasae to nearly 3 m (10 ft) in
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2624-624: The Royal Radnor Militia. In May 1813 he was admitted M.D. of St. Andrews University , and on 21 June 1813 he was elected professor of anatomy and surgery in the University of Dublin, and physician to Sir Patrick Dun's hospital. These offices he resigned in 1837, after he had raised the medical school to a much better position than it had ever before occupied. During almost the whole of his residence in Dublin Macartney
2706-468: The University of Dublin having refused to purchase it. He died at 31 Upper Merrion Street, Dublin, on 6 March 1843 (Gent. Mag. 1843, i. 554). He married on 10 Aug. 1795 a Miss Ekenhead. An ill-used and greatly misunderstood man, "he was," says Professor Alexander Macalister, an expert anatomist and a philosophical biologist far in advance of his period. His description of the vascular system of birds has in many respects not been surpassed, and his account of
2788-436: The air moving in a loop through the lungs when breathing. This was previously thought to only exist in the archosaurs ( crocodilians and birds ). This may be evidence that unidirectional airflow is an ancestral trait in diapsids . As with all amniotes, lizards rely on internal fertilisation and copulation involves the male inserting one of his hemipenes into the female's cloaca . Female lizards also have hemiclitorises ,
2870-412: The anatomy of mammals may be read with more profit than many modern works. In his account of the brain of the chimpanzee compared with that of an idiot, as well as in many others of his papers, there are glimpses of a morphology far beyond Cuvier, whose works he edited. His book on inflammation may be placed side by side with any pathological work of the period, while his researches on animal luminosity form
2952-461: The basis of many subsequent researches on the subject. Macartney discovered the fibrous texture of the white substance in the brain, and the connection between the subcortical nerve fibres and the grey matter of the cerebral hemispheres. He gave, too, the first satisfactory account of rumination in the herbivora, and he discovered numerous glandular appendages in the digestive organs of mammals, especially of rodents. As one of Warburton's advisers and as
3034-556: The case of the largest living varanid lizard, the Komodo dragon . Most lizards are fairly small animals. Lizards typically have rounded torsos, elevated heads on short necks, four limbs and long tails, although some are legless. Lizards and snakes share a movable quadrate bone , distinguishing them from the rhynchocephalians , which have more rigid diapsid skulls . Some lizards such as chameleons have prehensile tails, assisting them in climbing among vegetation. As in other reptiles,
3116-478: The distance between them; i.e., r ≪ R 1 {\displaystyle \ r\ll R_{1}} or R 2 {\displaystyle R_{2}} , so that equation (1) for the potential energy function simplifies to: with the force: The van der Waals forces between objects with other geometries using the Hamaker model have been published in the literature. From
3198-500: The distance to their prey before striking. Monitor lizards have acute vision, hearing, and olfactory senses. Some lizards make unusual use of their sense organs: chameleons can steer their eyes in different directions, sometimes providing non-overlapping fields of view, such as forwards and backwards at once. Lizards lack external ears, having instead a circular opening in which the tympanic membrane (eardrum) can be seen. Many species rely on hearing for early warning of predators, and flee at
3280-408: The electrostatic force is averaged out to a large extent because the molecules thermally rotate and thus probe both repulsive and attractive parts of the electrostatic force. Random thermal motion can disrupt or overcome the electrostatic component of the van der Waals force but the averaging effect is much less pronounced for the attractive induction and dispersion forces. The Lennard-Jones potential
3362-637: The endowed classical school at Armagh, and then at a private school. He was associated for a time with the Sheares brothers and Lord Edward Fitzgerald , the United Irishmen but, being dissatisfied with their programme, he cut himself adrift and began to study medicine. He apprenticed himself to William Hartigan (1756?–1812) on 10 Feb. 1793, his master being president of the Royal College of Surgeons of Ireland in 1797. Macartney also entered as
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3444-583: The environment. The chameleons in general use their ability to change their coloration for signalling rather than camouflage, but some species such as Smith's dwarf chameleon do use active colour change for camouflage purposes. The flat-tail horned lizard 's body is coloured like its desert background, and is flattened and fringed with white scales to minimise its shadow. Many lizards, including geckos and skinks , are capable of shedding their tails ( autotomy ). The detached tail, sometimes brilliantly coloured, continues to writhe after detaching, distracting
3526-439: The equilibrium distance. For individual atoms, the equilibrium distance is between 0.3 nm and 0.5 nm, depending on the atomic-specific diameter. When the interatomic distance is greater than 1.0 nm the force is not strong enough to be easily observed as it decreases as a function of distance r approximately with the 7th power (~ r ). Van der Waals forces are often among the weakest chemical forces. For example,
3608-454: The exchange of water, although more arid-living species have calcified shells to retain water. Inside the eggs, the embryos use nutrients from the yolk . Parental care is uncommon and the female usually abandons the eggs after laying them. Brooding and protection of eggs do occur in some species. The female prairie skink uses respiratory water loss to maintain the humidity of the eggs which facilitates embryonic development. In lace monitors ,
3690-652: The expansion of the dewlap as well as head-bobs and body movements add to the visual signals. Some species have deep blue dewlaps and communicate with ultraviolet signals. Blue-tongued skinks will flash their tongues as a threat display . Chameleons are known to change their complex colour patterns when communicating, particularly during agonistic encounters. They tend to show brighter colours when displaying aggression and darker colours when they submit or "give up". Several gecko species are brightly coloured; some species tilt their bodies to display their coloration. In certain species, brightly coloured males turn dull when not in
3772-406: The expression above, it is seen that the van der Waals force decreases with decreasing size of bodies (R). Nevertheless, the strength of inertial forces, such as gravity and drag/lift, decrease to a greater extent. Consequently, the van der Waals forces become dominant for collections of very small particles such as very fine-grained dry powders (where there are no capillary forces present) even though
3854-535: The extant non-avian reptiles. Archosauromorpha [REDACTED] [REDACTED] Pantestudines [REDACTED] † Kuehneosauridae [REDACTED] Rhynchocephalia [REDACTED] Squamata [REDACTED] Both the snakes and the Amphisbaenia (worm lizards) are clades deep within the Squamata (the smallest clade that contains all the lizards), so "lizard" is paraphyletic . The cladogram
3936-469: The force of attraction is smaller in magnitude than it is for larger particles of the same substance. Such powders are said to be cohesive, meaning they are not as easily fluidized or pneumatically conveyed as their more coarse-grained counterparts. Generally, free-flow occurs with particles greater than about 250 μm. The van der Waals force of adhesion is also dependent on the surface topography. If there are surface asperities, or protuberances, that result in
4018-471: The former being the microscopic description of the latter bulk property. The first detailed calculations of this were done in 1955 by E. M. Lifshitz . A more general theory of van der Waals forces has also been developed. The main characteristics of van der Waals forces are: In low molecular weight alcohols, the hydrogen-bonding properties of their polar hydroxyl group dominate other weaker van der Waals interactions. In higher molecular weight alcohols,
4100-442: The interactive forces between instantaneous multipoles in molecules without permanent multipole moments . In and between organic molecules the multitude of contacts can lead to larger contribution of dispersive attraction, particularly in the presence of heteroatoms. London dispersion forces are also known as ' dispersion forces', 'London forces', or 'instantaneous dipole–induced dipole forces'. The strength of London dispersion forces
4182-403: The intervening medium), and z is the center-to-center distance; i.e., the sum of R 1 , R 2 , and r (the distance between the surfaces): z = R 1 + R 2 + r {\displaystyle \ z=R_{1}+R_{2}+r} . The van der Waals force between two spheres of constant radii ( R 1 and R 2 are treated as parameters) is then
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#17327758762114264-487: The lizard to maintain their ideal body temperature for optimal mobility. Most social interactions among lizards are between breeding individuals. Territoriality is common and is correlated with species that use sit-and-wait hunting strategies. Males establish and maintain territories that contain resources that attract females and which they defend from other males. Important resources include basking, feeding, and nesting sites as well as refuges from predators. The habitat of
4346-548: The male tokay gecko is heard as "tokay-tokay!". Tactile communication involves individuals rubbing against each other, either in courtship or in aggression. Some chameleon species communicate with one another by vibrating the substrate that they are standing on, such as a tree branch or leaf. Lizards are found worldwide, excluding the far north and Antarctica, and some islands. They can be found in elevations from sea level to 5,000 m (16,000 ft). They prefer warmer, tropical climates but are adaptable and can live in all but
4428-499: The middle of the period. Mosasaurs likely evolved from an extinct group of aquatic lizards known as aigialosaurs in the Early Cretaceous . Dolichosauridae is a family of Late Cretaceous aquatic varanoid lizards closely related to the mosasaurs. The position of the lizards and other Squamata among the reptiles was studied using fossil evidence by Rainer Schoch and Hans-Dieter Sues in 2015. Lizards form about 60% of
4510-496: The molecular liquids, amount to 0.90 kJ/mol (9.3 meV) and 6.82 kJ/mol (70.7 meV), respectively, and thus approximately 15 times the value of the individual pairwise interatomic interactions (excluding covalent bonds ). The strength of van der Waals bonds increases with higher polarizability of the participating atoms. For example, the pairwise van der Waals interaction energy for more polarizable atoms such as S ( sulfur ) atoms in H 2 S and sulfides exceeds 1 kJ/mol (10 meV), and
4592-662: The most extreme environments. Lizards also exploit a number of habitats; most primarily live on the ground, but others may live in rocks, on trees, underground and even in water. The marine iguana is adapted for life in the sea. The majority of lizard species are predatory and the most common prey items are small, terrestrial invertebrates, particularly insects . Many species are sit-and-wait predators though others may be more active foragers. Chameleons prey on numerous insect species, such as beetles , grasshoppers and winged termites as well as spiders . They rely on persistence and ambush to capture these prey. An individual perches on
4674-542: The mouth, and is often long. In the beaded lizards, whiptails and monitor lizards, the tongue is forked and used mainly or exclusively to sense the environment, continually flicking out to sample the environment, and back to transfer molecules to the vomeronasal organ responsible for chemosensation, analogous to but different from smell or taste. In geckos, the tongue is used to lick the eyes clean: they have no eyelids. Chameleons have very long sticky tongues which can be extended rapidly to catch their insect prey. Three lineages,
4756-777: The observed solid aggregate state with bonding strengths comparable to covalent and ionic interactions. The strength of pairwise van der Waals type interactions is on the order of 12 kJ/mol (120 meV) for low-melting Pb ( lead ) and on the order of 32 kJ/mol (330 meV) for high-melting Pt ( platinum ), which is about one order of magnitude stronger than in Xe due to the presence of a highly polarizable free electron gas . Accordingly, van der Waals forces can range from weak to strong interactions, and support integral structural loads when multitudes of such interactions are present. More broadly, intermolecular forces have several possible contributions. They are ordered from strongest to weakest: When to apply
4838-441: The only venomous lizards. However, several species of monitor lizards, including the Komodo dragon , produce powerful venom in their oral glands . Lace monitor venom, for instance, causes swift loss of consciousness and extensive bleeding through its pharmacological effects, both lowering blood pressure and preventing blood clotting . Nine classes of toxin known from snakes are produced by lizards. The range of actions provides
4920-457: The painted dragon lizard Ctenophorus pictus is fading breeding colors. By manipulating superoxide levels (using a superoxide dismutase mimetic) it was shown that this fading coloration is likely due to gradual loss with lizard age of an innate capacity for antioxidation due to increasing DNA damage . The majority of lizard species are active during the day , though some are active at night , notably geckos. As ectotherms , lizards have
5002-431: The pairwise attractive van der Waals interaction energy between H ( hydrogen ) atoms in different H 2 molecules equals 0.06 kJ/mol (0.6 meV) and the pairwise attractive interaction energy between O ( oxygen ) atoms in different O 2 molecules equals 0.44 kJ/mol (4.6 meV). The corresponding vaporization energies of H 2 and O 2 molecular liquids, which result as a sum of all van der Waals interactions per molecule in
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#17327758762115084-467: The pairwise interaction energy between even larger, more polarizable Xe ( xenon ) atoms is 2.35 kJ/mol (24.3 meV). These van der Waals interactions are up to 40 times stronger than in H 2 , which has only one valence electron, and they are still not strong enough to achieve an aggregate state other than gas for Xe under standard conditions. The interactions between atoms in metals can also be effectively described as van der Waals interactions and account for
5166-399: The potential for new medicinal drugs based on lizard venom proteins . Genes associated with venom toxins have been found in the salivary glands of a wide range of lizards, including species traditionally thought of as non-venomous, such as iguanas and bearded dragons. This suggests that these genes evolved in the common ancestor of lizards and snakes , some 200 million years ago (forming
5248-510: The predator's attention from the fleeing prey. Lizards partially regenerate their tails over a period of weeks. Some 326 genes are involved in regenerating lizard tails. The fish-scale gecko Geckolepis megalepis sheds patches of skin and scales if grabbed. Many lizards attempt to escape from danger by running to a place of safety; for example, wall lizards can run up walls and hide in holes or cracks. Horned lizards adopt differing defences for specific predators. They may play dead to deceive
5330-414: The presence of lipids in gecko footprints. A later study suggested that capillary adhesion might play a role, but that hypothesis has been rejected by more recent studies. A 2014 study has shown that gecko adhesion to smooth Teflon and polydimethylsiloxane surfaces is mainly determined by electrostatic interaction (caused by contact electrification ), not van der Waals or capillary forces. Among
5412-478: The presence of rivals or females. While it is usually males that display, in some species females also use such communication. In the bronze anole , head-bobs are a common form of communication among females, the speed and frequency varying with age and territorial status. Chemical cues or pheromones are also important in communication. Males typically direct signals at rivals, while females direct them at potential mates. Lizards may be able to recognise individuals of
5494-487: The properties of the nonpolar hydrocarbon chain(s) dominate and determine their solubility. Van der Waals forces are also responsible for the weak hydrogen bond interactions between unpolarized dipoles particularly in acid-base aqueous solution and between biological molecules . London dispersion forces , named after the German-American physicist Fritz London , are weak intermolecular forces that arise from
5576-413: The relative orientation of the molecules. The induction and dispersion interactions are always attractive, irrespective of orientation, but the electrostatic interaction changes sign upon rotation of the molecules. That is, the electrostatic force can be attractive or repulsive, depending on the mutual orientation of the molecules. When molecules are in thermal motion, as they are in the gas and liquid phase,
5658-589: The right and left limbs with substantial body bending. This body bending prevents significant respiration during movement, limiting their endurance, in a mechanism called Carrier's constraint . Several species can run bipedally, and a few can prop themselves up on their hindlimbs and tail while stationary. Several small species such as those in the genus Draco can glide: some can attain a distance of 60 metres (200 feet), losing 10 metres (33 feet) in height. Some species, like geckos and chameleons, adhere to vertical surfaces including glass and ceilings. Some species, like
5740-526: The same species by their scent. Acoustic communication is less common in lizards. Hissing , a typical reptilian sound, is mostly produced by larger species as part of a threat display, accompanying gaping jaws. Some groups, particularly geckos, snake-lizards, and some iguanids, can produce more complex sounds and vocal apparatuses have independently evolved in different groups. These sounds are used for courtship, territorial defense and in distress, and include clicks, squeaks, barks and growls. The mating call of
5822-463: The scales. The dentitions of lizards reflect their wide range of diets, including carnivorous, insectivorous, omnivorous, herbivorous, nectivorous, and molluscivorous. Species typically have uniform teeth suited to their diet, but several species have variable teeth, such as cutting teeth in the front of the jaws and crushing teeth in the rear. Most species are pleurodont , though agamids and chameleons are acrodont . The tongue can be extended outside
5904-480: The shells. Larger species, such as monitor lizards, can feed on larger prey including fish, frogs, birds, mammals and other reptiles. Prey may be swallowed whole and torn into smaller pieces. Both bird and reptile eggs may also be consumed as well. Gila monsters and beaded lizards climb trees to reach both the eggs and young of birds. Despite being venomous, these species rely on their strong jaws to kill prey. Mammalian prey typically consists of rodents and leporids ;
5986-536: The skin of lizards is covered in overlapping scales made of keratin . This provides protection from the environment and reduces water loss through evaporation. This adaptation enables lizards to thrive in some of the driest deserts on earth. The skin is tough and leathery, and is shed (sloughed) as the animal grows. Unlike snakes which shed the skin in a single piece, lizards slough their skin in several pieces. The scales may be modified into spines for display or protection, and some species have bone osteoderms underneath
6068-412: The slightest sound. As in snakes and many mammals, all lizards have a specialised olfactory system, the vomeronasal organ , used to detect pheromones . Monitor lizards transfer scent from the tip of their tongue to the organ; the tongue is used only for this information-gathering purpose, and is not involved in manipulating food. Some lizards, particularly iguanas, have retained a photosensory organ on
6150-480: The subject. William Lawrence, FRS , a fellow lecturer and surgeon at St. Bartholomew's and a former pupil of Macartney, wrote articles on Insects, Reptiles and Vermes that Macartney did not have time to do. Van der Waals force In molecular physics and chemistry , the van der Waals force (sometimes van de Waals' force ) is a distance-dependent interaction between atoms or molecules . Unlike ionic or covalent bonds , these attractions do not result from
6232-478: The term "van der Waals" force depends on the text. The broadest definitions include all intermolecular forces which are electrostatic in origin, namely (2), (3) and (4). Some authors, whether or not they consider other forces to be of van der Waals type, focus on (3) and (4) as these are the components which act over the longest range. All intermolecular/van der Waals forces are anisotropic (except those between two noble gas atoms), which means that they depend on
6314-507: The top of their heads called the parietal eye , a basal ("primitive") feature also present in the tuatara . This "eye" has only a rudimentary retina and lens and cannot form images, but is sensitive to changes in light and dark and can detect movement. This helps them detect predators stalking it from above. Until 2006 it was thought that the Gila monster and the Mexican beaded lizard were
6396-435: The van der Waals forces between these surfaces and the spatulae , or microscopic projections, which cover the hair-like setae found on their footpads. There were efforts in 2008 to create a dry glue that exploits the effect, and success was achieved in 2011 to create an adhesive tape on similar grounds (i.e. based on van der Waals forces). In 2011, a paper was published relating the effect to both velcro-like hairs and
6478-503: The van der Waals interaction energy between spherical bodies of radii R 1 and R 2 and with smooth surfaces was approximated in 1937 by Hamaker (using London's famous 1937 equation for the dispersion interaction energy between atoms/molecules as the starting point) by: where A is the Hamaker coefficient , which is a constant (~10 − 10 J) that depends on the material properties (it can be positive or negative in sign depending on
6560-627: The young hatch close to 300 days, and the female returns to help them escape the termite mound where the eggs were laid. Around 20 percent of lizard species reproduce via viviparity (live birth). This is particularly common in Anguimorphs. Viviparous species give birth to relatively developed young which look like miniature adults. Embryos are nourished via a placenta -like structure. A minority of lizards have parthenogenesis (reproduction from unfertilised eggs). These species consist of all females who reproduce asexually with no need for males. This
6642-536: Was appointed a demonstrator of anatomy in the medical school in 1798. He was admitted a member of the Royal College of Surgeons of England on 6 Feb. 1800, began to practise in London as a surgeon, and was appointed lecturer on comparative anatomy and physiology at St. Bartholomew's Hospital, a post he held from March 1800 to 1811. On 21 Feb. 1811, he was elected F.R.S., and from 1803 to 1812 he served as surgeon to
6724-449: Was subjected to a very singular exhibition of petty persecution and open insult at the hands of some members of the board of Trinity College. He was denied the privilege of election to the fellowship of the Royal College of Surgeons, though he was made an honorary fellow of the Royal College of Physicians of Ireland in 1818. He also received an honorary M.D. from the University of Cambridge (31 Aug. 1833), to which he sold his museum in 1836,
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