Tentative interpretation of Hipparion incisors morphologies
Distinction between upper and lower incisors
In upper incisors the occlusal mark (enamel ring corresponding to the infundibulum) is farther away from the lingual border and closer to the vestibular than in the lowers; the crown is more curved (Fig.1).
Distinction between ‘evolved’ grazer forms and ‘primitive’ browsers
Lack or atrophy of third lower incisors is always a good character of evolved hipparions Fig.2).
When the third incisors are normally developed, the shape of the arcade – rounded or tending to be square – may provide some evidence (Fig.3).
Distinction between species whatever their stage of ‘evolution’
Occlusal diameters, flatness, presence of grooves and ridges on the crown and mark patterns on the occlusal surface should also be good indicators but they all are to some extent dependent on the degree of wear (Fig.4).
In conclusion, I believe that in Fig.5 the sorting of Shungura incisors into uppers (above) and lowers (below) is correct. I am not sure, however, that the Shungura C incisors do belong to another species than the others.