Lizards are a very large and widespread group of
squamate reptiles, with nearly 5,000
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 (reptiles with overlapping scales) which are neither
sphenodonts (i.e.,
Tuatara) nor
snakes. While the snakes are recognized as falling
phylogenetically within the
anguimorph lizards 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.
Lizards typically have limbs and external ears, while snakes lack both 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 a more primitive and solid
diapsid skull. Many lizards can detach their tails in order to escape from predators, an act called
autotomy, but this trait is not shared by all lizards. 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. The adult length of species within the
suborder ranges from a few
centimeters for some
chameleons and
geckos to nearly three meters (9 feet, 6 inches) in the case of the largest living varanid lizard, the
Komodo Dragon. Some extinct
varanids reached great size. The extinct aquatic
mosasaurs reached 17 meters, and the giant monitor
Megalania prisca is estimated to have reached perhaps seven meters.
Physiology
A feral Jackson's Chameleon from a population introduced to Hawaii in the 1970s.
Sight is quite 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 lizard also utilize 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.
A 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, the lizards erect the hyoid bone of their 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 lizards can often see UV.
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 "lizard" was superficially lizard-like, but had a solid, box-like skull, with openings only for eyes, nostrils, etc (termed
Anapsid). Turtles retain this skull form. Early anapsids later gave rise to two new groups with additional holes in the skull to make room for and anchor larger jaw muscles. Those with a single hole, the
Synapsids, gave rise to the superficially lizard-like
Pelycosaurs which include
Dimetrodon and the
Therapsids, including the
Cynodonts, from which would evolve the modern mammals.
The
Diapsids, possessing one
temporal fenestra before the eye and one behind it, continued to diversify. One branch, the
Archosaurs, retained the basic Diapsid skull, and gave rise to a bewildering array of animals, most famous being the crocodilians, the pterosaurs, the dinosaurs and their descendants, birds. The Ichthyosaurs and Plesiosaurs radiated from the same basal Diapsid group.
The smaller Lepidosaurs which would give rise to the lizards began to reduce the skull bones, making the skull lighter and more flexible. 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.
Lizard diversification
Within the
Lacertilia are found 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
Anoles mating, Gainesville, FL
The suborder
Iguania, found in Africa, south Asia, Australia, the New World, and with iguanas colonizing the islands of the west Pacific, form the
sister group to the remainder of the squamata. They are largely arboreal, and have primitively fleshy, non-prehensile tongues, 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 Iguanidae – American Arboreal Lizards, Chuckwallas, Iguanas, Iguanids
Gekkota
Active hunters, the
Gekkota includes three families comprising the distinctive cosmopolitan geckos and the legless flap-footed lizards of Australia and New Zealand. Like snakes, the geckos and the flap-footed lizards lack eyelids. Unlike snakes, they use their tongues to clean their often highly developed eyes. While gecko feet have unique surfaces which allow them to cling to glass and run on ceilings, the flapfoot has lost its limbs. The three families of this suborder are:
Relationship with humans
Komodo dragons on Rinca
Most lizard species are harmless to humans. Only the very largest lizard species pose threat of death; the
Komodo dragon, for example, has been known to stalk, attack, and kill humans. The venom of the
Gila monster and
beaded lizard is not usually deadly but they can inflict extremely painful bites due to powerful jaws. Numerous species of lizard are kept as
pets.
Lizard symbolism plays important, though rarely predominant roles in some
cultures (e.g.
Tarrotarro in
Australian Aboriginal mythology). The
Moche people of ancient
Peru worshiped 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.
s are eaten in Central America and
Uromastyx in
Africa. In North Africa, Uromastyx are considered
dhaab or 'fish of the desert' and eaten by nomadic tribes.
Classification
'''Suborder Lacertilia (Sauria) - (Lizards)
