Friday, 24 August 2007

Taxonomy of Pet Lizards and their Relatives

The taxonomy, or classification of pet lizards.

Scientific Classification
- the method by which biologists group and catagorize species and organisms

Kingdom: Animalia - from the Latin ‘animal', animalia is plural - group of organisms, multiceullular, responsive to environment and feed by consuming other organisms (or parts of them)

Phylum: Chordata - group of animals that includes vertebrates and several closely related invertebrate. They are defined by having, at some time in their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits an endostyle and a post-anal tail.

Superclass: Tetrapoda - from the Greek tetrapoda, Latin quadruped ‘four legged' - vertebrates with four feet, legs or leglike appendages.

Class: Sauropsida - represented by four surviving orders; crocodilia (crocodiles, caimans and alligatore) 23 species; sphenodontia (tuataras from New Zealand) 2 species; Squamata (lizards, snakes and amphisbenids or ‘worm lizards') approximatedly 7,900 species; Testudines (turtles and tortoises) approximately 300 species.

Order: Squamata - ‘scaled reptiles' is the largest recent order of reptiles. Distinguished by their skins, which bear horny scales or shields.

Suborder: Lacertilia - ‘lizards'

Family: Forty Families

Lizards are cold-blooded reptiles, characterised by having four legs, external ear openings and movable eyelids. The presence of eyelids and ears distinguishes lizards from true snakes, as does the lizard's tail, which can break off as a defence mechanism. Many lizards are capable of regenerating a lost limb or tail.

They also possess movable quadrate bones, making it possible to move the upper jaw relative to the braincase - particularly noticeable in snakes, which can swallow relatively large prey by opening their mouth very wide.

The adult lengh of lizards ranges from a few centimetres, for example Carribean Geckos, to nearly three metres - the Komodo Dragon...

Discovering Pet Lizards: Komodo Dragon

Many lizards can change color in response to their environments or in times of stress. The most familiar example is the chameleon, but more subtle color changes occur in other lizard species too.

New Findings
Until very recently, it was thought that only two lizard species were venomous: the Mexican beaded lizard and the closely-related Gila monster, both of which live in northern Mexico and the southwest United States.

However research at the University of Melbourne, Australia and Pennsylvania State University has revealed that in fact many lizards in the iguanians and monitor (lizard) families have venom-producing glands.

Typically these pose little danger to humans, as their poison is introduced slowly by chewing, rather than subcutaneous injection as with venomous snakes. Nine toxins previously thought to only occur in snakes have been discovered, as well as a number of previously unseen chemicals.

Before this discovery, swelling and bleeding from lizard bites was believed due to bacterial infection but is now known to be due to venom injection. These findings have caused a re-evaluation of the classification system for lizard species to form a venom clade and may result in radical changes to the beliefs regarding the evolution of lizard, snake and venom.

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 attack and kill humans and their livestock. The venom of the gila monster and beaded lizard is not deadly but they can inflict extremely painful bites due to powerful jaws.

Lizards in the Scincomorpha family, which include skinks (such as the blue-tongued skink), often have shiny, iridescent scales that appear moist. Like all other lizards, they are dry-skinned and generally prefer to avoid water. All lizards are capable of swimming if needed and a few (such as the Nile monitor) are quite comfortable in aquatic environments.


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