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. Amphibians of Oregon, Washington and British Columbia . Green, David M. and R. Wayne Campbell. 1984. The Amphibians of British Columbia . Permission is granted by the Vancouver Aquarium Marine Science Centre for classroom teachers to make copies for non-commercial use.