Well, I wouldn’t exactly call 10th c. new, but later than some others, yes.
Mongolians do not use surnames in the way that most Westerners, Chinese or Japanese do. Since the socialist period, patronymics — at that time called ovog,[10] now known as etsgiin ner — are used instead of a surname. If the father’s name is not legally established (i.e. by marriage) or altogether unknown, a matronymic is used. The patro- or matronymic is written before the given name.
Therefore, if a man with given name Tsakhia has a son, and gives the son the name Elbegdorj, the son’s full name, as it appears in passports and the like, is Tsakhia Elbegdorj. Very frequently, as in texts and speech, the patronymic is given in genitive case, i.e. Tsakhiagiin Elbegdorj, with (in this case) -giin being the genitive suffix. However, the patronymic is rather insignificant in everyday use and usually just abbreviated to an initial - Ts. Elbegdorj. People are normally just referred to and addressed by their given name (Elbegdorj guai - ‘Mr. Elbegdorj’), and the patronymic is only used to distinguish two people with a common given name. Even then, they are usually just distinguished by their initials, not by the full patronymic. There are cases in which a matronymic has been legally bestowed for one or the other reason, while a patronymic is known. If the patronymic is to be conveyed anyway, this can take a form like Altan Choi ovogt Dumaagiin Sodnom with the patronymic preceding the word ovog that takes the suffix -t ‘having’.
The basic differences between Mongolian and Anglo-Saxon names, in connection with trying to fit Mongolian names into foreign schemata, frequently lead to confusion. For example, O. Gündegmaa, a Mongolian shooter, is often incorrectly referred to as Otryad, i.e. by the (given) name of her father.
From Wikipedia.