Most land-dwelling vertebrates have rotating limbs terminating in digits, a characteristic useful for land movement. Biologists who assume that this characteristic evolved only after animals abandoned aquatic environments must consider the Acanthostega, a newly discovered ancestor of all land vertebrates. It possessed rotating limbs terminating in digits, but its skeleton was too feeble for land movement. It also breathed using only internal gills, indicating that it and its predecessors were exclusively aquatic. The statements above, if true, most strongly support which one of the following? ['Certain anatomical characteristics common to some aquatic animals represent an advantage for survival on land.', 'None of the anatomical characteristics common to most aquatic animals represent an advantage for survival on land.', 'Many anatomical characteristics common to most land animals represent a disadvantage for survival underwater.', 'Acanthostega originated as a land-dwelling species, but evolved gills only after moving to an underwater environment.']