The tadpole s tail also becomes smaller and becomes completely absorbed once a frog s metamorphosis is complete. It usually takes 10-12 weeks for a complete metamorphosis, but this is not true for every species. Some factors include food supply, temperature, salinity and the presence of other tadpoles. A group of frogs is called an army of frogs. When frogs swallow a meal, their eyeballs close and sink into their head.
Frogs hear using big round ears on their sides of their head, called typanum.
The biggest frog is the Goliath frog, Conraua goliath , from West Africa. Their bodies can exceed 30 cm from snout to vent. The smallest frog is the Brazilian Psyllophryne didactyla , which grows to only 9.8 mm. Most frogs are nocturnal. The earliest known frogs appeared in the late Jurassic period, about 190 million years ago.