Lizard

Lizard


Lizards are a widespread group of squamate
reptiles, with approximately 6,000 species, ranging across all continents except Antarctica,
as well as most oceanic island chains. The group, traditionally recognized as the suborder
Lacertilia, is defined as all extant members of the Lepidosauria that are neither sphenodonts
nor snakes – they form an evolutionary grade. While the snakes are recognized as falling
phylogenetically within the Toxicofera clade from which they evolved, the sphenodonts are
the sister group to the squamates, the larger monophyletic group, which includes both the
lizards and the snakes. Biology
Lizards typically have feet and external ears, while snakes lack both of these characteristics.
However, because they are defined negatively as excluding snakes, lizards have no unique
distinguishing characteristic as a group. Lizards and snakes share a movable quadrate
bone, distinguishing them from the sphenodonts, which have more primitive and solid diapsid
skulls. Many lizards can detach their tails to escape from predators, an act called autotomy.
Vision, including color vision, is particularly well developed in most lizards, and most communicate
with body language or bright colors on their bodies, as well as with pheromones. Lizards
are the most speciose among extant reptiles, comprising about 60% of all living species.
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 in
the case of the largest living varanid lizard, the Komodo dragon. Some extinct varanids reached
great size. The extinct aquatic mosasaurs reached 17 m, and the giant monitor Megalania
is estimated to have reached up to 7 m long. The name Sauria was coined by James Macartney;
it was the Latinisation of the French name Sauriens, coined by Alexandre Brongniart for
an order of reptiles in the classification proposed by the author, containing lizards
and crocodilians, later discovered not to be each other’s closest relatives. Later authors
used the term “Sauria” in a more restricted sense, i.e. as a synonym of Lacertilia, a
suborder of Squamata that includes all lizards but excludes snakes. This classification is
rarely used today because Sauria so-defined is a paraphyletic group. It was defined as
a clade by Jacques Gauthier, Arnold G. Kluge and Timothy Rowe as the group containing the
most recent common ancestor of archosaurs and lepidosaurs and all its descendants. A
different definition was formulated by Michael deBraga and Olivier Rieppel who defined Sauria
as the clade containing the most recent common ancestor of Choristodera, Archosauromorpha
and Lepidosauromorpha and all their descendants. However, neither of these uses have not gained
wide acceptance among researchers specializing in lizards.
Physiology Sight is very important for most lizards,
both for locating prey and for communication, and, as such, many lizards have highly acute
color vision. Most lizards rely heavily on body language, using specific postures, gestures,
and movements to define territory, resolve disputes, and entice mates. Some species of
lizards also use bright colors, such as the iridescent patches on the belly of Sceloporus.
These colors would be highly visible to predators, so are often hidden on the underside or between
scales and only revealed when necessary. The particular innovation in this respect
is the dewlap, a brightly colored patch of skin on the throat, usually hidden between
scales. When a display is needed, a lizard can erect the hyoid bone of its throat, resulting
in a large vertical flap of brightly colored skin beneath the head which can be then used
for communication. Anoles are particularly famous for this display, with each species
having specific colors, including patterns only visible under ultraviolet light, as many
lizards can see UV light. Shedding and regenerating tails
Lizard tails are often a different and dramatically more vivid color than the rest of the body
so as to encourage potential predators to strike for the tail first.
Many lizard species are capable of shedding part of their tails through a process called
autotomy. This is an example of the pars pro toto principle, sacrificing “a part for the
whole”, and is employed by lizards to allow them to escape when captured by the tail by
a predator. The detached tail writhes and wiggles, creating a deceptive sense of continued
struggle, distracting the predator’s attention from the fleeing prey animal.
The lizard will partially regenerate its tail over a period of weeks. The new section will
contain cartilage rather than bone, and the skin may be distinctly discolored compared
to the rest of the body. Evolution and relationships The retention of the basic ‘reptilian’ amniote
body form by lizards makes it tempting to assume any similar animal, alive or extinct,
is also a lizard. However, this is not the case, and lizards as squamates are part of
a well-defined group. The earliest amniotes were superficially lizard-like,
but had solid, box-like skulls, with openings only for eyes and nostrils, termed the anapsid
condition. Turtles retain, or have re-evolved, this skull form. Early anapsids later gave
rise to two new groups with additional holes in their skulls to make room for and anchor
larger jaw muscles. The synapsids, with a single fenestra, gave rise to the large, but
generally lizard-like pelycosaurs, which include Dimetrodon, a group which again gave rise
to the therapsids, including the cynodonts, from which the modern mammals would evolve.
The modern Tuatara retains the basic lepidosaur skull, distinguishing it from true lizards
in spite of superficial similarities. Squamates, including snakes and all true lizards, further
lightened the skull by eliminating the lower margin of the lower skull opening.
The earliest known fossil remains of a lizard belong to the iguanian species Tikiguania
estesi, found in the Tiki Formation of India, which dates to the Carnian stage of the Triassic
period, about 220 million years ago. However, doubt has been raised over the age of Tikiguania
because it is almost indistinguishable from modern agamid lizards. The Tikiguania remains
may instead be late Tertiary or Quaternary in age, having been washed into much older
Triassic sediments. Lizards are most closely related to a group called Rhynchocephalia,
which includes the tuatara. Rhynchocephalians first appeared in the Late Triassic, so it
can be inferred that the lizard-rhynchocephalian divergence occurred at this time and that
the earliest lizards appeared in the Triassic. Mitochondrial phylogenetics suggest that the
first lizards evolved in the late Permian. Most evolutionary relationships within the
squamates are not yet completely worked out, with the relationship of snakes to other groups
being the most problematic. On the basis of morphological data, iguanid lizards were thought
to have diverged from other squamates very early on, but recent molecular phylogenies,
both from mitochondrial and nuclear DNA, do not support this. Because snakes have a faster
molecular clock than other squamates, and few early snake and snake ancestor fossils
have been found, resolving the relationship between snakes and other squamate groups is
difficult. Lizard diversification
Lacertilia comprises four generally recognized suborders, Iguania, Gekkota, Amphisbaenia
and Autarchoglossa, with the “blind skinks” in the family Dibamidae having an uncertain
position. While traditionally excluded from the lizards, the snakes are usually classified
as a clade with a similar subordinal rank. Iguania The suborder Iguania, found in Africa, southern
Asia, Australia, the New World and the islands of the west Pacific, forms the sister group
to the remainder of the squamata. The various species are largely arboreal, and have primitively
fleshy, non-prehensile tongues, some even have scales, but this condition is obviously
highly modified in the chameleons. This clade includes the following families:
Family Agamidae – agamid lizards, Old World arboreal lizards
Family Chamaeleonidae – chameleons Family Corytophanidae – helmet lizards
Family Crotaphytidae – collared lizards, leopard lizards
Family Hoplocercidae – dwarf and spiny-tail iguanas
Family Iguanidae – American arboreal lizards, chuckwallas, iguanas, iguanids
Family Opluridae – Malagasy iguanas Family Phrynosomatidae – North American
spiny lizards Family Polychrotidae – anoles and kin
Family Tropiduridae – tropidurid lizards Gekkota
Active hunters, the Gekkota include three families comprising the distinctive cosmopolitan
geckos and the legless, flap-footed lizards of Australia and New Guinea. Like snakes,
the flap-footed lizards and most geckos lack eyelids. Unlike snakes, they use their tongues
to clean their often highly developed eyes. While gecko feet have unique surfaces that
allow them to cling to glass and run on ceilings, the flap-foot has lost its limbs. The three
families of this suborder are: Family Eublepharinae – ‘eyelid’ geckos
Family Gekkonidae – geckos Family Pygopodidae – flap-footed lizards
Relationship with humans Most lizard species are harmless to humans.
Only the largest lizard species, the Komodo dragon, which reaches 3.3 m in length and
weighs up to 166 kg, has been known to stalk, attack, and, on occasion, kill humans. An
eight-year-old Indonesian boy died from blood loss after an attack in 2007. The venoms of
the Gila monster and beaded lizard are not usually deadly, but they can inflict extremely
painful bites due to powerful jaws. Numerous species of lizard are kept as pets,
including bearded dragons, iguanas, anoles, and geckos. Some lizards have an affinity
for humans, but many are suspicious or skittish around them. Lizards that bite humans are
very rare. Lizards are predominantly insectivorous, but some eat fruit, or vegetables. Live crickets
and worms are the most typical foods for pet lizards, though the crested gecko can feed
entirely on fruit. Lizard symbolism plays important, though rarely
predominant, roles in some cultures. The Moche people of ancient Peru worshipped animals
and often depicted lizards in their art. According to a popular legend in Maharashtra, a common
Indian monitor, with ropes attached, was used to scale the walls of the Sinhagad fort in
the Battle of Sinhagad. Green iguanas are eaten in Central America,
where they are referred to sometimes as “chicken of the tree” after their habit of resting
in trees and their supposed chicken-like taste, and spiny-tailed lizards are eaten in Africa.
In North Africa, Uromastyx species are considered dhaab or ‘fish of the desert’ and eaten by
nomadic tribes. Classification Suborder Lacertilia –
Family †Bavarisauridae Family †Eichstaettisauridae
Infraorder Iguania Family †Agamidae
Family †Arretosauridae Family †Euposauridae
Family Corytophanidae Family Iguanidae
Family Phrynosomatidae Family Polychrotidae
Family Leiosauridae Family Tropiduridae
Family Liolaemidae Family Leiocephalidae Family Crotaphytidae
Family Opluridae Family Hoplocercidae
Family †Priscagamidae Family †Isodontosauridae
Family Agamidae Family Chamaeleonidae Infraorder Gekkota
Family Gekkonidae Family Pygopodidae
Family Dibamidae Infraorder Scincomorpha
Family †Paramacellodidae Family †Slavoiidae
Family Scincidae Family Cordylidae
Family Gerrhosauridae Family Xantusiidae
Family Lacertidae Family †Mongolochamopidae
Family †Adamisauridae Family Teiidae
Family Gymnophthalmidae Infraorder Diploglossa
Family Anguidae Family Anniellidae
Family Xenosauridae Infraorder Platynota
Family Varanidae Family Lanthanotidae
Family Helodermatidae Family †Mosasauridae See also
Sexual selection in lizards Notes References
Behler, John L.; King, F. Wayne. The Audubon Society Field Guide to Reptiles and Amphibians
of North America. New York: Alfred A. Knopf. p. 581. ISBN 0-394-50824-6. 
Capula, Massimo; Behler, John L.. Simon & Schuster’s Guide to Reptiles and Amphibians of the World.
New York: Simon & Schuster. ISBN 0-671-69098-1.  Cogger, Harold; Zweifel, Richard. Reptiles
& Amphibians. Sydney: Weldon Owen. ISBN 0-8317-2786-1.  Conant, Roger; Collins, Joseph. A Field Guide
to Reptiles and Amphibians Eastern/Central North America. Boston, Massachusetts: Houghton
Mifflin Company. ISBN 0-395-58389-6.  Ditmars, Raymond L. Reptiles of the World:
The Crocodilians, Lizards, Snakes, Turtles and Tortoises of the Eastern and Western Hemispheres.
New York: Macmillian. p. 321.  Freiberg, Dr. Marcos; Walls, Jerry. The World
of Venomous Animals. New Jersey: TFH Publications. ISBN 0-87666-567-9. 
Gibbons, J. Whitfield. Their Blood Runs Cold: Adventures With Reptiles and Amphibians. Alabama:
University of Alabama Press. p. 164. ISBN 978-0-8173-0135-4.  Rosenfeld, Arthur. Exotic Pets. New York:
Simon & Schuster. p. 293. ISBN 0671636901.  Further reading
Pianka, Eric R.; Vitt, Laurie J.. Lizards: Windows to the Evolution of Diversity. Berkeley,
Calif.: Univ. of California Press. ISBN 9780520248472.  External links
Data related to Sauria at Wikispecies Lizard Gallery
 Ernest Ingersoll. “Lizard”. Encyclopedia Americana. 
The Lizards Living in Qatar. 2014. First edition, Published in Doha, 2014, 5 June. 570 pages.
ISBN 978-9927-93-12-9

Randy Schultz

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