Fig. 9

Evolutionary history of Tachyoryctoides. 1 Decrease in size, 2 increase in size, 3 mesolophid of m1 disappears, 4 mesoloph of M1 and M2 tends to be reduced (4′) or absent (4″), 5 lingual part of aneterolophid becomes shorter and anterosinusid becomes smaller on m2 and m3, 6 the anterolophulid of m1 disappears, 7 posterior part of M3 reduced, 8 posterolophs of upper molars become shorter, 9 posterosinusid of m3 disappears, 10 M3 with closed posterosinus, 11 posterosinus of M1 and M2 becomes closed; WS white sandstone of middle member of the Xianshuihe Formation; asterisk between WS II and WS III