| − | The '''hoatzin''' (''Opisthocomus hoatzin'') is a South American bird whose chief characteristic is a pair of claws on each wing when young, presenting an evolutionary problem. | + | The '''hoatzin''' (''Opisthocomus hoatzin'') is a South American bird whose chief characteristic is a pair of claws on each wing when young. The development of this feature cannot be explained by the [[Theory of Evolution]]. |