What is "arsinoitheriidae"

Arsinoitheriidae is a family of extinct hoofed mammals belonging to the extinct order Embrithopoda. Remains have been found in the Middle East, Africa, Asia and Romania. When alive, they would have had a great, albeit very superficial, resemblance to the modern rhinoceros. Despite this, they were not closely related to rhinoceri (or any other perissodactyl), instead being more related to hyraxes, elephants, sirenians, and possibly desmostylians.