Triadobatrachus ('triple-frog') is an extinct genus of frog-like amphibian, including only one known species, Triadobatrachus massinoti. It is the oldest frog known to science, and an excellent example of a transitional fossil. It lived during the Early Triassic, in what is now Madagascar.

 Triadobatrachus was 10 centimetres (3.9 in) long, and still retained many primitive characteristics, such as possessing fourteen vertebrae, where modern frogs have only four to nine. Six of these vertebrae formed a short tail, which the animal retained as an adult. It probably swam by kicking its hind legs, although it could not jump, as most modern frogs can. Its skull resembled that of modern frogs, consisting of a latticework of thin bones separated by large openings. As evidenced by its large ear openings, Triadobatrachus possessed good hearing.

 This creature, or a cousin, evolved eventually into modern frogs, the earliest example of which is Sanyanlichan, millions of years later in the late Jurassic.

 It was first discovered on 1937, when Adrien Massinot, near the village of Betsieka in northern Madagascar, found an almost complete skeleton. The animal must have fossilized soon after its death, because all bones lay in their natural position. Only the anterior part of the skull and the ends of the limbs were missing.

 Although it was found in marine deposits, the general structure of Triadobatrachus shows that it may have lived for part of the time on land and breathed air. Its proximity to the mainland is further borne out by the remains of terrestrial plants found together with it.

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