Notostylops murinis (Ameghino 1897, Riggs and Patterson 1935; 75cm in esitmated length; Eocene; FMNH-P13319) is widely considered a 'notoungulate' a clade that has been split into several parts in the large reptile tree. Here it nests with the above specimen of Ectocion in the clade of elephants, rock hyraxes and sea cows.
The jaws narrowed anteriorly. The anterior incisors were enlarged, like those of rodents. The mandible was more robust. No canines were present. The premolars were molarized.