Crocodile - Crocodile

Japanese: ワニ(鰐) - ワニ

A general term for the order Crocodilians of the class Reptilia. There are about 23 extant species known, distributed in freshwater and inlets in tropical and subtropical regions around the world. Their bodies are covered with hard scales, and their large heads have developed jaws and rows of large, sharp, tank-shaped teeth. Their external nostrils open at the end of their snouts, and only their nostrils, eyes, and ears are above the water's surface, showing their adaptation to life in water. Their external nostrils have valves that close underwater. Their eyes have a nictitating membrane. Their cloaca is parallel to the body axis, and they have a single penis without a bladder. Their heart is almost complete with two atria and two ventricles, and their lungs are more evolved than those of other reptiles. They are oviparous. Fossils have been known since the end of the Triassic period, and the family Crocodilidae, which includes all extant species, appeared at the end of the Mesozoic era. There are various theories on the classification of extant species, but they are often divided into two families, Alligatoridae and Crocodylidae. They do not naturally occur in Japan. Their leather products are highly valued and expensive, and as a result of overhunting, the population of each species has drastically decreased and they are now under protection. → Nile crocodile → Related topics Reptiles

Source : Heibonsha Encyclopedia About MyPedia Information

Japanese:

爬虫(はちゅう)綱ワニ目の総称。現生種は23種ほど知られ，世界の熱帯，亜熱帯の淡水および入江付近に分布する。体はかたい鱗板でおおわれ，大きな頭部には顎が発達して，槽生(そうせい)の大きな鋭い歯が並ぶ。外鼻孔は吻(ふん)端に開き，鼻孔，眼，耳のみが水面上に出るよう，水中生活への適応がみられる。外鼻孔は弁を備え水中では閉じられる。眼には瞬膜がある。総排出腔は体軸に平行，陰茎は１本で膀胱(ぼうこう)を欠く。心臓はほぼ完全な２心房２心室，肺も他の爬虫類に比べ進化している。卵生。三畳紀末期から化石が知られ，中生代末には現生の全種を含むワニ科が現れた。現生種の分類には諸説あるが，アリゲーター科とクロコダイル科の２科に分けられることが多い。日本には自然分布をしない。皮革製品は高価で珍重され，狩猟の対象として乱獲が続けられた結果，各種とも激減し保護下にある。→ナイルワニ
→関連項目爬虫類

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