A New Species of 

Merychippus

By J. P. BUWALDA and G. E. LEWIS

•

A SHORTER CONTRIBUTION TO GENERAL GEOLOGY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 264-G

Description of a new species of horse from 

the middle Miocene, and descriptions of 

three new geologic formations

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1955
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington 25, D. C. - Price 15 cents (paper cover)
CONTENTS

—————

Introduction-_________________________________________________________________________________________________ 147

Witnet, Kinnick, and Bopesta formations in Tehachapi Mountains, Calif____--_____-----------_-------___------- —— - 147

Geologic occurrence of Merychippus tehachapiensis-. _________________________-_____-_______-_--.------.-.-----_------- 148

Systematic description_________________________________________________________________________________________ 148

Stratigraphic significance-_----_______________-_____-_____________________-_-_-_-__--_-------------------------- 149

Literature cited--____-__--__--_-___-__--__________-_____________________-____-________-_-_--------_----------- 150

ILLUSTRATIONS

Page 

FIGURE 12. Merychippus tehachapiensis Buwalda and Lewis: type, CIT 4919___-_--_------_---_-_--------------_----_ 150

13. Merychippus tehachapiensis Buwalda and Lewis: A and B, CIT 4920; C and D, TIC 21685_________________ 151

14. Merychippus tehachapiensis Buwalda and Lewis: TIC 11817____________________________________________ 151

15. Merychippus tehachapiensis Buwalda and Lewis: TIC 21688__-___-____-_-------------_---_-.-------------- 152

16. Merychippus tehachapiensis Buwalda and Lewis: A and B, CIT 4919+CIT 4920.

Merychippus intermontanus Merriam: C and D, UC 21399+TJC 21400_______________--___-___-_----__-- 152

A SHORTER CONTRIBUTION TO GENERAL GEOLOGY

A NEW SPECIES OF MERYCHIPPUS

By J. P. BUWALDA and G. E. LEWIS

ABSTRACT

Merychippus tehachapiensis, a new species of middle Miocene 

horse, is described and named from the Kinnick formation of the 

. Tehachapi Mountains, Calif. M. tehachapiensis is believed to 

be a reliable indicator of pre-Barstovian age in the Mojave Desert 

and nearby California areas because its morphology and stratigraphic position are similar to those of M. primus of the middle 

Miocene Sheep Creek local fauna in the Hemingford group of 

Nebraska.

Three new formations, the pre-middle Miocene Witnet, the 

middle Miocene Kinnick, and the late Miocene Bopesta are 

described and named.

INTRODUCTION

The senior author : published (1916) the preliminary 

description of a new species of Merychippus after collecting some of the material described in the present paper 

during the years 1914 and 1915. He named the fauna 

with which this Merychippus was associated the Phillips 

Ranch fauna, but did not name the new species. 

Twenty years after the first collection of this fauna was 

made, he also published (1934 and 1935, in abstract) a 

brief statement on the geology of the locality (UC 

locality 2577, equivalent to CIT locality 503 2 ).

The University of California has made further collections at this and nearby localities, and in recent years 

Messrs. E,. H. Tedford and R. L. Shultz, Jr., have 

collected considerable material for the California 

Institute of Technology. We are indebted to them and 

to the University for permission to describe the type 

and hypodigm material. The study of this and related 

material from other localities was carried out in Pasadena at the California Institute. Mr. David P. 

Willoughby prepared the illustrations.

The material described herein was collected from a 

single locality. Collections made by the U. S. Geological Survey from other areas in southern California in 

recent years have included this same new species of 

horse, whose occurrence will be described in forthcoming reports by the junior author.

1 Professor Buwalda died August 19,1954.

2 CIT=»California Institute of Technology; UC=University of California at 

Berkeley. Where not otherwise specified, numbers following these abbreviations are 

catalogue numbers.

321590—55——2

WITNET, KINNICK, AND BOPESTA FORMATIONS IN 

TEHACHAPI MOUNTAINS, CALIFORNIA

WITNET FORMATION

This sedimentary formation is exposed chiefly along 

Cache Creek and lower Oil Canyon about 5 miles 

northeast of Monolith, Kern County, Calif., and is 

herein named from Witnet Ridge north of lower Oil 

Canyon. It consists mainly of alternate beds of coarse 

gray arkose, locally bouldery, and of dark sandy shale. 

It is probably of continental origin, and its thickness 

is more than 4,000 feet. It has yielded no fossils, but 

its age is probably early Tertiary and certainly premiddle Miocene. The strata are steeply tilted and in 

part overturned. The formation crops out as a strip 

Yz to % mile wide and 4 miles long along Cache Creek 

and Oil Canyon. Neither the top nor the bottom of the 

formation is exposed; at the lower contact the granitic 

basement rocks are thrust over it, and the youngest 

beds are covered by gently dipping Miocene strata 

that overlie the upper part of the Witnet formation 

with strong angular unconformity.

}Type section.—Lower Oil Canyon about 1 mile above 

its junction with Cache Creek; NW % of Sec. 13, T32S, 

R34E, M D B and M, Mojave Quadrangle; Tehachapi 

Quadrangle.

Name Witnet formation first used by Buwalda (1934).

KINNICK FORMATION

'The Kinnick formation is herein named from Kinnick 

Ridge, north of the confluence of Cache, Oil, and Sand 

Creeks. It consists mainly of stratified, green, basic 

volcanic tuffs, largely ash beds with some coarse 

agglomerates; the upper part consists of gray sandy 

shale with, locally, white freshwater diatomaceous 

beds and cherts. There are some basic lava flows. The 

thickness is not less than 1,500 feet. The formation is 

exposed over wide areas west of Cache Creek from 

Monolith northward for 6 or more miles. The strata 

are moderately deformed with dips generally not more 

than 30 degrees. The shales of the upper part contain 

the Phillips Ranch vertebrate local fauna of middle

147
148 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

Miocene age. The Kinnick formation lies with strong 

angular unconformity across the edges of the Witnet 

formation. It probably bears conformable relations to 

the overlying Bopesta formation.

Type section.—Base at unconformity north of the 

confluence of Cache, Oil and Sand creeks (SW corner 

of Sec. 11, T32S, R34E, M D B and M), thence northward through CIT locality 503 in saddle west of Hill 

5,015, Mojave Quadrangle, in NW ft of Sec. 34, T31S, 

R34E, M D B and M.

Name Kinnick formation first used by Buwalda

(1934).

BOPESTA FORMATION

The Bopesta formation is herein named from Bopesta 

Ridge, southwest of Cache Peak. It consists of tan 

and white, fine and coarse, quartzose sandstones containing some ash and volcanic debris, a few conglomeratic beds, and some gray sandy shale beds. The 

formation is exposed widely in conspicuous badlands 

areas east of upper Cache Creek 6 to 7 miles northeast 

of Monolith, Kern County, Calif., and extending under 

Cache Peak. The thickness is probably not less than 

3,500 feet. The beds are moderately deformed, with 

dips as much as 30 degrees. The Cache Peak vertebrate 

local fauna, which occurs in the lower and middle part, 

is late Miocene in age. Probably conformable on the 

Kinnick formation but contrasts strongly with it as 

a mappable unit through its coarseness of materials. 

Overlain by basic lavas, probably unconformably.

Type section.—From near the confluence of Cache 

Creek and its East Fork (which heads on the south side 

of Cache Peak) in the NW % of Sec. 1, T32S, R34E, 

M D B and M, to the north side of Cache Peak, which 

is in Sec. 20, T31S, R35E, M D B and M.

Name Bopesta formation first used by Buwalda 

(1934).

GEOLOGIC OCCURRENCE OF MERYCHIPPUS 

TEH A CHAPIENSIS

The type and hypodigm material of Merychippus 

tehachapiensis was found in the Phillips Ranch local 

fauna of the Kinnick formation (CIT locality 503=UC 

locality 2577), in strata consisting mainly of gray shale 

and fine sandstone, both ashey, interbedded with chert 

and freshwater diatomite, with a maximum thickness 

of a few hundreds of feet.

The Bopesta formation which contains an upper 

Miocene vertebrate fauna (Cache Peak local fauna) 

overlies the Kinnick formation. Partly because of the 

sharp difference in lithology, which changes from the 

gray shale and well-stratified fine sandstone of the 

upper part of the Kinnick, that may represent playa 

deposits, to the coarse, poorly stratified tan and red 

sandstone and conglomerate of the Bopesta, but especially because of the supposed contrast in the merychippine species in the two formations, it was formerly 

believed that they represented lower and upper Miocene 

rocks, that middle Miocene rocks were missing, and 

that the Bopesta formation unconformably overlay the 

Kinnick. We now believe that at least the upper part 

of the Kinnick formation, which yields the Phillips 

Ranch local fauna, is of middle Miocene stratigraphic 

position.

Probably the stratigraphic range of Merychippus 

tehachapiensis and that of the larger merychippine 

species of the Bopesta overlap. The sedimentary section seems to be continuous, and the sandstone of the 

Bopesta formation conformably overlies shale of the 

Kinnick. Messrs. Tedford and Schultz reported the 

discovery of teeth of the larger merychippine species 

at the locality that yielded the type specimen of M. 

tehachapiensis, and of one specimen probably referable 

to M. tehachapiensis in the lower part of the coarse 

sandstone regarded as belonging to the Bopesta formation. Perhaps the different environments indicated by 

the dissimilar upper part of the Kinnick formation 

(shale, chert, and diatomite) and the Bopesta formation 

(sandstone and conglomerate), rather than the tune 

interval, determined the change in the most numerous 

species of Merychippus occupying the region in Miocene time. However, only a few teeth of the larger, 

advanced species of Merychippus have been found in 

the Kinnick, and, excepting the specimen found near 

its base, M. tehachapiensis has not been reported from 

the Bopesta. Detailed study of structural features of 

adjoining parts of the Kinnick and Bopesta has not 

yielded evidence of an unconformity.

SYSTEMATIC DESCRIPTION

Family EQUIDAE Gray, 1821 

Subfamily EQUINAE Steinmann and Doderlein, 1890

Genus MERYCHIPPUS leidy, 1857

Merychippus tehachapiensis, new species

Figures 12-16

Type.—Fragment of right maxilla with P4 and M1 , 

and associated right P2, all only moderately worn; 

CIT 4919 from CIT locality 503 (fig. 12).

Hypodigm material.—Associated left M1 , M2, and 

M3, CIT 4920 from CIT locality 503 (fig. 13); left M1 

and M2 , CIT 4921 from locality 503; fragmentary rami 

with left P3 , P4 , M!, M2 , M3 and right P3 , P4, Mt , M2 , 

UC 11817 from UC locality 2577 (fig. 14); fragmentary 

ramus with right P2 and P3 , UC 21688 from UC locality 

2577 (fig. 15); left M3 , UC 21685 from UC locality 2577 

(fig. 13); and additional specimens from CIT locality 

503 (=UC locality 2577).

Stratigraphic position.—Kinnick formation, middle 

Miocene of Hemingfordian age.
A NEW SPECIES OP MERYCHIPPUS 149

Locality.—Phillips Ranch, north half of Sec. 34, 

T31S, R34E, Kern County, California (U. S. Army 

Corps of Engineers Map of Tehachapi Quadrangle, 

coordinates 1266.8—1359.4).

Diagnosis.—The diameters and heights of the crowns 

of the cheek teeth are about 85 to 90 percent those of 

the type of Merychippus primus (Osborn) (see Osborn, 

1918), with similar enamel pattern and other morphologic features, except that the upper premolars tend to 

be somewhat narrower in proportion to their length 

than in M. primus. The cheek teeth are further advanced 

morphologically beyond Parahippus but, individually 

and in series, are about the same length as in M. gunteri 

Simpson; however, they tend to be proportionally narrower and with crowns as much as 50 percent higher 

than the highest reported for M. gunteri. The morpho 

logically similar cheek teeth range from somewhat 

smaller to about the same size in plan, but from 10 to 

15 percent higher-crowned, and with protocone further 

forward than in M. carrizoensis Dougherty. The cheek 

teeth are about one-quarter smaller, and lower crowned 

than in M. stevensi Dougherty.

The elliptical protocone is broadly connected to the 

protoconule a very short distance from the apex of the 

unworn protocone in protohippine fashion. The permanent cheek teeth have a relatively thin coating of 

cement. The fossettes of the permanent cheek teeth 

are lined but not at all filled with cement. The postprotoconal valley is more nearly filled with cement than 

the fossettes, and usually communicates with the prefossette where the crochet fails to touch or fuse with

the protoloph for about the apical half of the unworn 

crown height. Many of the permanent upper cheek 

teeth have well-wrinkled fossette walls in early stages 

of wear, with the usual progressive simplification in the 

increasingly advanced stages of wear; many have a 

single, or even double, pli caballin, either incipient or 

well-developed. However, the degree of enamel complication is far from constant. The milk molars are 

very thinly and incompletely covered with cement, and 

are slightly larger but otherwise very similar to those 

of M. insignis Leidy.

The senior author's original description and comparisons (1916, p. 78-79, 82-83) are amended and 

supplemented by the present diagnosis. The table 

below indicates the sizes of the figured specimens.

STRATIGRAPHIC SIGNIFICANCE

The senior author's descriptions of the geologic occurrence of Merychippus tehachapiensis in the Tehachapi Mountains (Buwalda, 1916, 1934, 1935, and this 

report) indicate that this rather primitive species was 

outlived by the larger and more advanced species of 

Merychippus found in the Cache Peak local fauna of 

that region.

The junior author's recent studies of specimens collected from the Mojave Desert in the Barstow, Calif., 

area by the U. S. Geological survey establish the 

presence of Merychippus tehachapiensis in Miocene 

rocks of that region. Probably M. tehachapiensis and 

certain other species of fossil vertebrates found in the

Specimen

CIT 4919 P2 P4 

M1

CIT 4920 M1 M2 

M3

UC 11817 P3 

P4 

Mt 

M2 

P3-M2

UC 21688 P2 

UC 21685 M3

Measurements in millimeters

Length

18.9 

15.7

15.7

15.8 

15.0 

14.2

16.8 

14.8 

16.1 

16.3 

65.0

15.8 

19.7

Width

14.2 

16.9 

17.5

17.1 

16.5 

15.7

9.6 

9.6 

9.0

7.7

8.9 

7.5

Crown 

height

16.0 

16.0 

13.9

1 14.0 

16.5 

20.0

20.5 

20.5

23.0

Stage of wear

Medium. 

Early medium. 

Medium.

Advanced medium. 

Medium. 

Earliest slight.

Early medium. 

Early medium. 

Medium. 

Slight.

Slight. 

Slight.

i Estimated.
150 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

Barstow area are characteristic of a stratigraphic position below that of the typical upper Miocene fauna of 

the Barstow formation as that formation and its fauna 

are generally understood.

Merychippus tehachapiensis, although notably smaller 

and having lower-crowned cheek teeth, is a good 

structural ancestor for M. intermontanus, the typical 

Barstow horse, as shown in figure 16. These are demonstrable differences in stage of evolution of two 

different species of the same genus in the same area. 

The specific diagnosis pointed out the morphologic 

similarity of M. tehachapiensis to M. primus and M. 

carrizoensis. This evidence seems to warrant acceptance of M. tehachapiensis as a fossil that is diagnostic 

of middle Miocene stratigraphic position about equivalent to that of the Hemingfordian Sheep Creek local 

fauna, with a stratigraphic position well below that of 

the typical Barstow fauna.

LITERATURE CITED

Buwalda, J. P., 1916, New mammalian faunas from Miocene 

sediments near Tehachapi Pass in the southern Sierra 

Nevada: Univ. Calif. Pub., Dept. Geology Bull. 10, p. 

75-85.

———— 1934, Tertic tectonic activity in Tehachapi region (abs.): 

Pan-Amer. Geologist, v. 61, p. 309-310.

1935, Tertiary tectonic activity in the Tehachapi region

(abs.); Proc. Geol. Soc. America for 1934, p. 312-313. 

Osborn, H. F., 1918, Equidae of the Oligocene, Miocene, and 

Pliocene of North America, iconographic type revision: 

Am. Mus. Nat. History Mem. (new ser.), v. 2, p. 102-104, 

fig. 78.

vy~-

FIGURE 12. Merychippus tehachapiensis Buwalda and Lewis, n. sp., X 2. Type: A, buccal and B, occlusal views of fragment of right maxilla with P* and MI, and associated right P*, CIT^4919 from CIT locality 503.
A NEW SPECIES OF MERYCHIPPUS 151

FIGURE 13. Merychippus tehachapiemis Buwalda and Lewis, n. sp., X 2. A, buccal and B, occlusal views of associated left MI, M2 , and M3 , CIT 4920 from CIT locality

503; <7, occlusal and D, lingual views of left M3 , UC 21685 from UC locality 2577

FIGURE 14. Merychippus tehachapiensis Buwalda and Lewis, n. sp., X 2. A, occlusal view of cheek teeth and B, lingual view of fragment of left ramus with P3 , P4 , MI, Mj, 

and partly erupted M3 ; C, occlusal view of cheek teeth of fragment of right ramus with Pa, Pi, Mi, and M2 ; UC 11817 from UC locality 2577.
152 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

B

FIOUPE 15. Merychippus tehachapiensis Buwalda and Lewis, n. sp., X 2. A, occlusal 

view and B, view of posterior end of fragment of right ramus with Pj 

and P3 , UC 21688 from UC locality 2577.

FIOTJBE 16. Merychippus tehachapiensis Buwalda and Lewis, n. sp., natural size. Restoration of right upper dental arcade with A, occlusal view of the series P>-M», and B,

buccal view of right M2 , based on CIT 4919 and 4920; for comparison with M. intermontanus below.

Merychippus Mermontanus Merriam. natural size. Restoration of right upper dental arcade with C, occlusal view of the series P2-Ms, and D, buccal view of

right M2; after Merriam, based on UC 21399 and 21400.