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Venomous mammals are animals of the class Mammalia that produce venom, which they use to kill or disable prey, or to defend themselves from predators or conspecifics. In modern nature, venomous mammals are rare. Mammalian venoms form a heterogeneous group having different compositions and modes of action and are present in three orders of mammals, Insectivora, Monotremata, and Chiroptera. A fourth order, Primates, is proposed to have venomous representatives.〔 To explain the rarity of venom delivery in Mammalia, Mark Dufton of the University of Strathclyde has suggested that modern mammalian predators do not need venom because they are able to kill quickly with their teeth or claws, whereas venom, no matter how sophisticated, requires time to disable prey. Venom is much more common among other vertebrates; there are many more species of venomous reptiles (e.g. venomous snakes), and fish (e.g. stonefish). There is no known species of venomous bird. However, some birds are poisonous to eat or touch, and ''Sinornithosaurus'', a dinosaur related to birds, may have had a venomous bite. There are only a few species of venomous amphibians; certain salamandrid salamanders can extrude sharp venom-tipped ribs.〔(【引用サイトリンク】title=Venomous Amphibians (Page 1) - Reptiles (Including Dinosaurs) and Amphibians - Ask a Biologist Q&A )〕 ==Definitions== Several definitions of venomous animals have been proposed.〔 Bücherl states that venomous animals must possess at least one venom gland, a mechanism for excretion or extrusion of the venom, and apparatus with which to inflict wounds. Mebs states that venomous animals produce venom in a group of cells or gland, and have a tool, the venom apparatus, which delivers the venom by injection during a bite or sting. The venom apparatus in this definition encompasses both the gland and the injection device, which must be directly connected. Fry et al. stated that a venom is a secretion produced in a specialized gland in one animal and delivered to a target animal through the infliction of a wound. This secretion must contain molecules that disrupt normal physiological processes so as to facilitate feeding or defense by the producing animal. Additionally, the feeding secretion of hematophagous specialists (e.g. vampire bats) may be regarded as a specialized subtype of venom. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Venomous mammal」の詳細全文を読む スポンサード リンク
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