Eskimo–Aleut languages
The Eskimo population of settlement of Сиреники (Sireniki, plural of Sirenik) formerly spoke an Eskimo language with several peculiarities not only among Eskimo languages, but even compared to Aleut. For example, dual number is not known in Sirenik Eskimo, while most Eskimo–Aleut languages have dual, including the neighboring Siberian Yupik relatives. The peculiarities amounted to mutual unintelligibility with Siberian Yupik and Sirenik Eskimo's nearest language relatives. The language is now extinct.