Page 25 - maxson1928

22,

Faunal Relationships

The Mint Canyon series is one of the southernmost of the

California ·Tertiary vertebrate horizons lying within the Pacific Coast

marine province. Situated immediately south of the Mohave Desert area

it is perhaps not surprising to find a relationship between the Barstow

and Mint Canyon faunas.

Ln both the Virgin Valley and Barstow occurrences anchitheriine

horses accompany the more progressive types. This association is found also

in the Mint Ca.nyon fauna. That the more primitive types of horses continued

to exist in the upper Miocene and lower Pliocene is shown by the fossil

record at several localities in the Great Basin.

rrhe protohippine forms of both the Barstow and the Mint Ca.nyon

are approximately at the same evolutionary stage. Merychippu.s intermontanus

is difficult to separate generically from Protohippus. In the milk

dentition of the Barstow form as well as in the permanent dentition

characters closely resemble those of Protohippus. This lack of definite

distinction was noted by Dr. J.C. Merriam in his discussion of the

Barstow horses.

The smaller form assigned to Merychippus californicus is more

advanced than M. isonesus o:f the Mascall and more primitive than M. sumani

of the Barstow. It appears specifically identical with the type recorded

from the Temblor Miocene of the north Coalinga region. Merriamts work on

the Merychippus fauna of this horizon indicates that the zone represents

the faunal stage of Tu.rritella ocoyana and the stratigraphic stage of the

"Temblor 11 beds of F. M. Anderson. On the basis of the stage of evolution

of the mammals evidenced by types from the Great Basin province the age

of the Coalinga occurrence would be considered more recent than on the baais

of percentage of' marine molluscan species characterizing this horizon.