カピバラ（Hydrochoerus hydrochaeris）は、テンジクネズミ科カピバラ属に分類される齧歯類。ヒメカピバラH. isthmiusと2種でカピバラ属を構成する。別名オニテンジクネズミ（鬼天竺鼠）。学名はギリシャ語で水の豚を意味し、漢名も水豚と呼ばれる。現生種の齧歯類では最大の種である。南アメリカ東部アマゾン川流域を中心とした、温暖な水辺に生息する。

呼び名

グアラニー語の「ka'apiûara（細い草を食べる者）」にちなみ、それがスペイン語に転訛して「Capibara」と呼ばれるようになった。日本では同じ言語の「Kapiyva」（草原の主）に由来するとの説が一般に広く流布しているが明確な根拠はない。和名はオニテンジクネズミ（鬼天竺鼠）。なお、日本ではしばしば誤ってカピパラやカビパラと表記されることもある。

形態

体長106 - 134センチメートル。体重オス35 - 64キログラム、メス37- 66キログラムと現生の齧歯類でも最大。

体毛はタワシのような手触りの硬く長いもので、体を震わせるだけで水を落とすことが出来る。

前肢の指は4本、後肢の趾は3本。指趾の間には小型の水かきがある。下顎の大臼歯は左右に4本ずつ（他のテンジクネズミ科は3本ずつであったため区別されていた）あり、第1 - 3大臼歯の3本と、第4大臼歯1本の大きさがほぼ等しい。肛門の周囲に臭腺（肛門腺）がある。

オスは鼻面に卵状に盛り上がった毛で被われない臭腺（モリージョ）が発達するが、メスではほとんど発達しない。

The capybara (Hydrochoerus hydrochaeris) is a rodent classified in the genus Hydrochoerus within the family Caviidae. Together with the lesser capybara (H. isthmius), it constitutes the genus Hydrochoerus. It is also known as the giant cavy (oni-tenjikunezumi in Japanese). Its scientific name means "water pig" in Greek, and its Chinese name (水豚) also translates to "water pig." It is the largest living rodent species. Capybaras inhabit warm watersides, mainly in the Amazon River basin of eastern South America. Etymology Its name derives from the Guaraní word "ka'apiûara," meaning "eater of slender grass," which was adapted into Spanish as "capibara." In Japan, the theory that the name comes from the Guaraní word "Kapiyva" (master of the grasslands) is widely circulated, though it lacks clear evidence. Its Japanese name is oni-tenjikunezumi (giant cavy). In Japan, it is also often mistakenly written as "kapipara" or "kabipara." Morphology Capybaras measure 106 to 134 centimeters in head-and-body length. Males weigh 35 to 64 kilograms, while females weigh 37 to 66 kilograms, making them the largest of all living rodents. Their fur is long and coarse, feeling much like a scrub brush, allowing them to shake off water with just a quick shiver of their body. They have four toes on their front feet and three on their hind feet. There is small webbing between their toes. Capybaras have four molars on each side of the lower jaw (which previously set them apart from other cavies, which have three), with the combined size of the first through third molars roughly equal to that of the fourth molar alone. Scent glands (anal glands) are located around the anus. Males develop a prominent, hairless, oval-shaped scent gland (morillo) on the snout, which is largely undeveloped in females.