The term was initially used as a general adjective for animals that could live on land or in water, including seals and otters.
ðə tˈɜːm wʌz ɪnˈɪʃəli jˈuːzd æz ɐ dʒˈɛnɚɹəl ˈædʒɪktˌɪv fɔːɹ ˈænɪməlz ðæt kʊd lˈɪv ˌɔn lˈænd ɔːɹ ɪn wˈɔːɾɚ, ɪŋklˈuːdɪŋ sˈiːlz ænd ˈɑːɾɚz.