Chameleons!

May 6, 2010 by · Leave a Comment 

tufail

Chameleons (family Chamaeleonidae) are a distinctive and highly specialized clade of lizards. They are distinguished by their parrot-like zygodactylous feet, their separately mobile and stereoscopic eyes, their very long, highly modified, and rapidly extrudable tongues, their swaying gait, the possession by many of a prehensile tail, crests or horns on their distinctively shaped heads, and the ability of some to change color. Uniquely adapted for climbing and visual hunting, the approximately 160 species of chameleon range from Africa, Madagascar, Spain and Portugal, across south Asia, to Sri Lanka, have been introduced to Hawaii, California and Florida, and are found in warm habitats that vary from rain forest to desert conditions.

Chameleons vary greatly in size and body structure, with maximum total length varying from 3.3 cm (1.3 in.) in Brookesia minima (one of the world’s smallest reptiles) to 68.5 cm (27 in.) in the male Furcifer oustaleti. Many have head or facial ornamentation, such as nasal protrusions, or horn-like projections in the case of Chamaeleo jacksonii, or large crests on top of their head, like Chamaeleo calyptratus. Many species are sexually dimorphic, and males are typically much more ornamented than the female chameleons.

Chameleon species have in common their foot structure, eyes, lack of ears, and tongues.

Their eyes are the most distinctive among the reptiles. The upper and lower eyelids are joined, with only a pinhole large enough for the pupil to see through. They can rotate and focus separately to observe two different objects simultaneously. It in effect gives them a full 360-degree arc of vision around their body. When prey is located, both eyes can be focused in the same direction, giving sharp stereoscopic vision and depth perception. They have very good eyesight for reptiles, letting them see small insects from a long (5-10 cm) distance.

They lack a vomeronasal organ. Also, like snakes, they do not have an outer or a middle ear. This suggests that chameleons might be deaf, although it should be noted that snakes can sense vibration using a bone called the quadrate. Furthermore, some or maybe all chameleons, can communicate via vibrations that travel through solid substrates such as branches.

Chameleons have very long tongues (sometimes longer than their own body length) which they are capable of rapidly extending out of the mouth.

Tongue structure

The tongue extends out faster than human eyes can follow, at around 26 body lengths per second. The tongue hits the prey in about 30 thousandths of a second.[4] The tongue of the chameleon is a complex arrangement of bone, muscle and sinew. At the base of the tongue there is a bone and this is shot forward giving the tongue the initial momentum it needs to reach the prey quickly. At the tip of the elastic tongue there is a muscular, club-like structure covered in thick mucus that forms a suction cup.[5] Once the tip sticks to a prey item, it is drawn quickly back into the mouth, where the chameleon’s strong jaws crush it and it is consumed. Ultraviolet light is part of the visible spectrum for chameleons.[6] Chameleons exposed to ultraviolet light show increased social behavior and activity levels, are more inclined to bask and feed and are also more likely to reproduce as it has a positive effect on the pineal gland

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Islands

May 3, 2010 by · Leave a Comment 

ibn tufail 4-25-10

An island or isle is any piece of land that is surrounded by water. Very small islands such as emergent land features on atollsare called islets. A key or cay is another name for a small island or islet. An island in a river or lake may be called an eyot. A grouping of geographically or geologically related islands is called an archipelago.

An island may still be described as such despite the presence of a land bridge, for example Singapore and its causeway, or the various Dutch delta islands, such as IJsselmonde. Some places may even retain “island” in their names for historical reasons after being connected to a larger landmass by a wide land bridge, such as Coney Island.

There are two main types of islands: continental islands and oceanic islands. There are also artificial islands. There is no standard of size which distinguishes islands from islets and continents.

The word island comes from Old English igland (from ‘ig’, similarly meaning ‘island’ when used independently, and -land carrying its contemporary meaning). However, the spelling of the word was modified in the 15th century by association with the etymologically unrelated Old French loanword isle, which itself comes from the latin word insula. Old English ‘ig’ is actually a cognate of Latin aqua(water).

Continental islands are bodies of land that lie on the continental shelf of a continent. Examples include Greenland and Sable Island off North America;Barbados and Trinidad off South America; Great Britain, Ireland and Sicily offEurope; Sumatra, Borneo and Java off Asia; and New Guinea, Tasmania and Kangaroo Island off Australia.

A special type of continental island is the microcontinental island, which results when a continent is rifted. Examples are Madagascar and Socotra offAfrica; New Zealand; the Kerguelen Islands; and some of the Seychelles.

Another subtype is an island or bar formed by deposition of tiny rocks where a water current loses some of its carrying capacity. An example is barrier islands, which are accumulations of sand deposited by sea currents on the continental shelf. Another example is islands in river deltas or in large rivers. While some are transitory and may disappear if the volume or speed of the current changes, others are stable and long-lived. Islets are very small islands.

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