Defense mechanisms Reptile

Many small reptiles such as snakes and lizards which live on the ground or in the water are vulnerable to being preyed on by all kinds of carnivorous animals. Thus avoidance is the most common form of defense in reptiles. At the first sign of danger, most snakes and lizards crawl away into the undergrowth, and turtles and crocodiles will plunge into water and sink out of sight.
A camouflaged Phelsuma deubia on a palm frond

Reptiles may also avoid confrontation through camouflage. Using a variety of grays, greens, and browns, these animals can blend remarkably well into the background of their natural environment.

If the danger arises so suddenly that flight may be harmful, then crocodiles, turtles, some lizards, and some snakes hiss loudly when confronted by an enemy. Rattlesnakes rapidly vibrate the tip of the tail, which is composed of a series of nested, hollow beads.

If all this does not deter an enemy, different species will adopt different defensive tactics.

Snakes use a complicated set of behaviors when attacked. Some will first elevate their head and spread out the skin of their neck in an effort to look bigger and more threatening. Failure of this may lead to other measures practiced particularly by cobras, vipers, and closely related species, who use venom to attack. The venom is modified saliva, delivered through fangs from a venom gland. Some non-venomous snakes, such as the corn snake, play dead when in danger.

When a crocodile is concerned about its safety, it will gape to expose the teeth and yellow tongue. If this doesn't work, the crocodile gets a little more agitated and typically begins to make hissing sounds. After this, the crocodile will start to change its posture dramatically to make itself look more intimidating. The body is inflated to increase apparent size. If absolutely necessary it may decide to attack an enemy.
A White-headed dwarf gecko with shed tail

Some species try to bite immediately. Some will use their heads as sledgehammers and literally smash an opponent, some will rush or swim toward the threat from a distance, even chasing them onto land or galloping after them.

Geckos, skinks, and other lizards that are captured by the tail will shed part of the tail structure through a process called autotomy and thus be able to flee. The detached tail will continue to wiggle, creating a deceptive sense of continued struggle and distracting the predator's attention from the fleeing prey animal. The animal can 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. The tails are often a separate and dramatically more vivid color then the rest of the body, as to attract potential predators to strike for the tail first.

World's of Mammals

Mammals (formally Mammalia /məˈmeɪli.ə/) are members of a class of air-breathing vertebrate  animals  characterized by the possession of hair, three middle ear bones, and mammary glands functional in mothers with young. Most mammals also possess sweat glands and specialized teeth, and the largest group of mammals, the placentals, have a placenta  which feeds the offspring during gestation. The mammalian brain, with its characteristic neocortex, regulates endothermic  and circulatory systems, including a four-chambered heart. Mammals range in size from the 30–40 millimeter (1- to 1.5-inch) Bumblebee Bat to the 33-meter (108-foot) Blue Whale.

According to Mammal Species of the World, which is updated through periodic editions, 5676 species were known in 2005, distributed in 1,229 genera, 153 families and 29 orders. In 2008 the IUCN completed a 5-year, 17,000 scientist Global Mammal Assessment for its IUCN Red List, which counted 5488 accepted species at the end of that period. The class is divided into two subclasses (not counting fossils): the Prototheria (order of Monotremata) and the Theria, the latter containing the infraclasses Metatheria (including marsupials) and Eutheria (the placentals). The classification of mammals between the relatively stable class and family levels having changed often, different treatments of subclass, infraclass and order appear in contemporaneous literature, especially for Marsupialia.

Except for the five species of monotremes (which lay eggs), all living mammals give birth to live young. Most mammals, including the six most species-rich orders, belong to the placental group. The three largest orders, in descending order, are Rodentia (mice, rats, porcupines, beavers, capybaras, and other gnawing mammals), Chiroptera (bats), and Soricomorpha (shrews, moles and solenodons). The next three largest orders, depending on classification scheme, include the Primates, to which the human species belongs, the Cetartiodactyla (including the even-toed hoofed mammals and the whales) and the Carnivora (dogs, cats, weasels, bears, seals, and their relatives).

The early synapsid mammalian ancestors, a group which included pelycosaurs such as Dimetrodon, diverged from the amniote line that would lead to reptiles at the end of the Carboniferous period. Preceded by many diverse groups of non-mammalian synapsids (sometimes referred to as mammal-like reptiles), the first true mammals appeared 220 million years ago in the Triassic period. Modern mammalian orders appeared in the Palaeocene and Eocene epochs of the Palaeogene period. Phylogenetically, the clade Mammalia is defined as all descendants of the most recent common ancestor of monotremes (e.g., echidnas and platypuses) and therian mammals (marsupials and placentals). This means that some extinct groups of "mammals" are not members of the crown group Mammalia, even though most of them have all the characteristics that traditionally would have classified them as mammals. These "mammals" are now usually placed in the unranked clade Mammaliaformes.