 UA 8699 is a worn and broken left lower molar . Part of the trigonid ( the front group of cusps ) , at the <unk> ( inner front ) corner of the tooth is missing . Krause estimated that the complete tooth would have been 3 @.@ 5 mm ( 0 @.@ 14 in ) long and 2 @.@ 2 mm ( 0 @.@ 09 in ) wide . The tooth is tribosphenic , like that of modern mammals , as indicated by a number of features , including the broad basin of the talonid ( the back group of cusps ) , and the acute angle ( 48 ° ) between the cusps of the trigonid . UA 8699 lacks a <unk> ( ridge ) resembling a shelf on the lingual ( inner ) side , indicating that is not a member of Australosphenida ( the proposed clade uniting monotremes and some ancient Gondwanan mammals , including the Jurassic Madagascan Ambondro ) ; thus , it can be identified as representing Boreosphenida , which includes marsupials , placentals , and their extinct relatives . 
