CONTRIBUTIONS TO PAIJEONTOLOGY I PLESIPPUS FRANCE.SCANA (FRICK) FROM THE LATE PLIOCENE, COSO MOUNTAINS, CALIFORNIA With a REVIEW OF THE GENUS PLESIPPUS BY JOHN R. SCHULTZ With three plates and three text-figures [Preprinted from Carnegie Institution of Washington Publication No. 473, pagee 1 to 13, May 21, 1936] .Bakh\..iit:J .. .-,..: Sc!iod v: the Go!oloiico:lSc~ Cuti/ornia J11 !'a!.;:tc (•i' T~chnolOgy PasoJena, Culi{ornia Contribution N o. 1 7 8 ' CONTRIBUTIONS TO PALJEONTOLOGY I PLESIPPUS FRANCESCANA (FRICK) FROM THE LATE PLIOCENE, COSO MOUNTAINS, CALIFORNIA With a REVIEW OF THE GENUS PLESIPPUS BY JOHN R. SCHULTZ [Issued May 21, 1936] PLESIPPUS FRANCE! PLIOCENE, COSi Two mammalian types, Coso Mountains, Californil more abundant forms in t Plesippus. These are of pa CONTENTS relation of the geologic ho: of their phylogenetic relati Page make a comparative study Introduction.... 3 Mountains with reference List of Localities. .. 3 similar age and to define Plesippus francescana (Frick) . 5 attempted, the position of Description of Material ..................................... : . 5 The writer is under ob] Additional Species Referred to Plesippus ........................... .. :,. ... .- . 7 nity to study the collectior Plesippus simplicidens (Cope). 7 for his constant interest anc Plesippus cumminsii (Cope).. 8 E. L. Furlong and R. W. " Plesippus proversus (Merriam). 8 and suggestions. Thanks Plesippus shoshonensis Gidley ...... ~ - . .. 8 for permission to study th Plesippus idahoensis (Merriam) ..................... ..... ·. 8 ensis, and to the U. S. Na Key to Species of Plesippus................................................... 9 senting this species from Status of the Genus Plesippus. 10 f rancescana was loaned th Ancestry of the Equus. 11 reontology, University of Plesippus-like Types of Eurasia and Northern Africa............................. 12 prepared by Mr. John L. 2 LI~ Calif. Inst. Locality 118- miles northwest of Grand Vii Calif. Inst. Locality 119- locality 118, Owyhee Count: Calif. Inst. Locality 131 Olancha, Inyo County, Cal topographical continuation eastern portion of Owens Vi Calif. Inst. Locality 210- River near Hagerman, Idah Calif. Inst. Locality (un1l junction with Los Muerto (Plesippus proversus.) Univ. of Calif. Locality ~ the San Joaquin Valley, Ca Plesippus proversus.) 1 R. W. Wilson, Jour. Mamn 263-266, 1932. PLESIPPUS FRANCE.SCANA (FRICK) FROM THE LATE PLIOCENE. COSO MOUNTAINS, CALIFORNIA INTRODUCTION Two mammalian types, occurring in a late Pliocene fauna from the Coso Mountains, California, have already been described.1 Among the more abundant forms in this assemblage are the horses of the genus Plesippus. These are of particular interest not only for purposes of cor­ relation of the geologic horizon in which they occur, but also because of their phylogenetic relationships. Opportunity is taken therefore to Page make a comparative study of characters of the species from the Coso .. .. .. .. 3 Mountains with reference to nearly related forms found in beds of . 3 similar age and to define more clearly, than has been previously . 5 attempted, the position of Plesippus in the lineage of the horse group. 5 The writer is under obligation to Dr. Chester Stock for opportu­ . 7 nity to study the collection, for critical reading of the manuscript, and . 7 for his constant interest and guidance during the investigation. Messrs. 8 E. L. Furlong and R. W. Wilson have contributed valuable discussions . .. 8 and suggestions. Thanks are expressed to the Los Angeles Museum . 8 for permission to study the mounted specimen of Plesippus shoshon­ . .. 8 ensis, and to the U.S. National Museum for loan of material repre­ . 9 senting this species from Hagerman, Idaho. The type of Plesippus . 10 francescana was loaned through the kindness of the Museum of Pal­ . 11 reontology, University of California. The illustrations have been . 12 prepared by Mr. John L. Ridgway. LIST OF LOCALITIES Calif. Inst. Locality 118-Immediately north of the Snake River, thirteen miles northwest of Grand View, Ada County, Idaho. <Plesippus idahoensis.) Calif. Inst. Locality 119-0n south side of the Snake River and opposite locality 118, Owyhee County, Idaho. (Plesippus idahoens-is.) Calif. Inst. Locality 131-Western flanks of Coso Mountains east of Olancha, Inyo County, California. The Coso Range forms a southward topographical continuation of the Inyo Mountains and bounds the south­ eastern portion of Owens Valley. (Plesippus francescana.) Calif. Inst. Locality 210-U. S. National Museum quarry site on the Snake River near Hagerman, Idaho. (Type of Plesippus shoshonens-is.) Calif. Inst. Locality (unnumbered)-Valley of Tres Pinos Creek near its junction with Los Muertos Creek, San Benito Quadrangle, California. (Plesippus proversus.) Univ. of Calif. Locality 2079-North Coalinga region, western border of the San Joaquin Valley, California, Upper Etchegoin formation. (Type of Plesippus proversus.) 1 R. W. Wilson, Jour. Mammalogy, vol. 13, 100-154, 1932; C. Stock, ibid., vol. 13, 263-266, 1932. 4 CONTRIBUTIONS TO PALJEONTOLOGY PLESIPPUS FRANCESCANJ ffniv. of Calif. Locality 303t eight miles southwest of Cal Plesippus idahoensis.) Univ. of Calif. Locality 32 SE 14 Sec. 9, T. 3S, R. 2W., U francescana.) Univ. of Texas-Crosby Co Plesippus simplicidens.) Univ. of Texas-Mont Blan (Type of Plesippus cumminsii Plesip Although no complete skulls cene beds of the Coso Mounta teeth, jaws, and numerous sk of Pliohippus francescana Fx California fails to disclose all' the material from the Coso ~ collection now available perm Additional characters are: I (2) nearly vertical position o: tocone in the last two premi in individual lower cheek-ti Reasons for referring the sp will be more fully discussed E OESCF Material-A mandible, No No. 847 (Plate 2, fig. 2) ; thr and 4) ; three lower milk tee mentary mandibular rami f specimens in the collection 1 from Calif. Inst. Tech. Vert. General Characters of Sk1 indicate a form of large ~ caballus. The cheek-teeth cemented crowns. The incis like that in the modern genw Since a detailed description result in a repetition of Frie: Upper Deciduous Cheek-~ and flatter than the mesosti FIG. I-Upper cheek-tooth series of species of Plesippus. a, type of P., fran­ round. Both fossettes are i cescana {Frick), No. 2m7 Univ. of Calif. Coll., Loe. 3253, right side {reversed in printing); b, P. francescana, referred specimen, No. 847, Calif. Inst. Loe. 131, plications. A well-develope right side reversed {in printing); c, P. simplicidens {Cope) after Matthew the hypocone in Dp~ and : {reversed); d, P. proversus {Merriam); e, P. shoshonensis Gidley; f, P. idaho­ cusp in Dp1.. The protoc01 ensis {Merriam), No. 1852, Calif. Inst. Loe. 119; g, P. idahoensis {Merriam), is flattened and is slightly i No. 892, Calif. Inst. Loe. 118. All figures X lh. pli caballin is present. For Lower Deciduous Cheek-' anteroexternal enamel fold 1 Childs Frick, Univ. Calif. Pul: NTOLOGY PLESIPPUS FRANCESCANA FROM COSO MOUNTAINS, CALIFORNIA 5 Univ. of Calif. Locality 3036C-Near Froman Ferry on the Snake River, eight miles southwest of Caldwell, Idaho, Idaho formation. (Type of Plesippus idahoensis.) Univ. of Calif. Locality 3253-Elsinore Quadrangle, central portion of SE% Sec. 9, T. 3S, R. 2W., Upper San Timoteo beds. (Type of Plesippus francescana.) . Univ. of Texas-Crosby County, Texas, Blanco Canyon bed. (Type of Plesippus simplicidens.) Univ. of Texas-Mont Blanco, Crosby County, Texas, Blanco formation. (Type of Plesippus cumminsii.) Plesippus francescana (Frick) Although no complete skulls were found, the collection from the late Plio­ cene beds of the Coso Mountains includes several series of upper and lower teeth, jaws, and numerous skeletal elements. Comparison with specimens of Pliohippus francescana Frick from the San Timoteo beds of southern California fails to disclose any difference except that of size. Consequently the material from the Coso Mountains is referred to Frick's species. The collection now available permits a supplementary description of this form. Additional characters are: (1) presence of a large and functional Pl, (2) nearly vertical position of the upper incisors, (3) flattening of the pro­ tocone in the last two premolars, (4) presence of a vestigial protostylid in individual lower cheek-teeth, (5) characters of the milk dentition. Reasons for referring the species to Plesippus rather than to Pliohippus will be more fully discussed elsewhere in this paper. DESCRIPTION OF MATERIAL Material-A mandible, No. 902 (Plate 1); a series of upper cheek-teeth, No. 847 (Plate 2, fig. 2); three upper milk teeth, No. 1847 (Plate 2, figs. 3 and 4); three lower milk teeth, No. 1848 (Plate 2, fig. 1) ; numerous frag­ mentary mandibular rami and maxillaries; various limb elements. All specimens in the collection of the California Institute of Technology and from Calif. Inst. Tech. Vert. Pale. Locality 131. General Characters of Skull and Dentition-The mandibular specimens indicate a form of large size, comparable in this character to Equus caballus. The cheek-teeth are long with moderately curved and well­ cemented crowns. The incisors have a procumbent position approximately like that in the modern genus. A large and functional Pl is always present. Since a detailed description of the permanent cheek-teeth would merely result in a repetition of Frick's exposition,1 it has been omitted. Upper Deciduous Cheek-Teeth-In these teeth the parastyles are larger and flatter than the mesostyles. The external borders of the fossettes are