Not only does this species of Darwin's frog (Rhinoderma darwinii) have a really unique morphology, but it also has two very unusual behaviors.
Males exhibit a mouth-brooding behavior wherein the tadpoles develop inside the male's vocal sac. They are direct developers, which means there is no free-living larval stage. Prior to hatching, the male gulps the eggs into his vocal sac where they remain past hatching and develop inside the vocal sac for upwards of 70 days! At the end of metamorphosis the froglets emerge and begin life among the leaf litter. This frog also has the unusual defensive strategy of playing dead when threatened; it rolls over on its back and remains motionless. If it is near a stream when frightened, it may jump into the stream and float in the water on its back!
Darwin's frogs were originally described by Darwin himself during the voyage of the HMS Beagle in Chile. They are currently distributed throughout Chile and Argentina, but have experienced significant population declines as a result of habitat loss, largely due to conversion of native forests to tree plantations.
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For more information, check out Amphibiaweb!