Page 18 - maxson1928

15,

In many respects these teeth indicate affinity with Hippar.2:2.£.

In size and in some features of the enamel pattern the Mint Canyon form

closely resembles Merychippus eohipparion Osborn from the Pawnee Creek

beds of northeastern Colorado. The metaconid is well separated from the

metastylid in P . The metaconid-metastylid pillars are widely separated
2
but the groove does not flatten out near the base of the crown as in

M. eohipparion. This may be regarded as an advanced character.

Ot'her characters serve to distinguish these teeth from those of

Merychippus. In cross-section they exceed the most advanced merychippine

types. In one of the teeth the metaconid-metastylid groove is broad and

not so sharply indented as is usu.ally the case in 1,~erychippus. The

enwnel pattern of the crown differs from that of the large Barstow forms.

The pattern of the grinding surface shows some remarkable

similarities to that of Hipparion condoni Merriam from the Ellensburg

formation of southern Washington. 'fue antero-posterior diameter of the

metaconid-metastylid column is even greater than that of H. condoni

and is comparable to that of other species of Hipparion. Valleys adjacent

to the metaconid-metastylid column are compressed and emphasize its large

proportions. On the protoconid of each tooth is a prominent antero-external

ridge as in H. condonL Flattening of the exterior margins of protoconid

and hypoconid is not so mar;~ecl as in H. condoni and in other species of

Hipparion. The metaconid-metastylid groove although broad is still

somewhat more sharply demarcated in the m.nt Canyon specimen than in

H. condoni. The entostylid and entoconid are compressed and are not

separated as in the Ellensburg type. The entoconid has developed an

anterior lobe, an unusual character in Merychippus, but it 1s not so fully

rounded as in Hipparion, Moreover, the length of the crowns does not seem

as great (taking into consideration wear) as in llipparion.