Skull proportions, excluding the size of the preorbital ‘bar’ (32) : Lakotahippus s.l.

As the variation is the largest for measures of the fossa, especially its distance from the orbit (’bar’ : mesure 32), I have drawn separate ratio digrams for other dimensions : 5=post-palatal length ; 23=anterior ocular line ; 2=palatal length ; 1=muzzle length ; 15=maximal muzzle breadth ; 9=P2-M3 length ; 30=length of the naso-incisival notch ; 31=length of the cheek. The reference is the skull FAM 60300 of Lakotahippus (Tables 1 doc2262 and 2 doc2265).

Lakotahippus, Lakotahippus-like, and Group A-morph 9 skulls.

There are only two skulls (7269 from John Day, referred to Kalobatippus ; and 10828, referred to Protohippus or Neohipparion) that somehow resemble the reference Lakotahippus 60300 from Ash Hollow (Lakotalike).
All other have much shorter naso-incisival notches and/or longer cheeks ; they evidently belong to Group A. They form the morph 9 of Group A (A-9).