PROMERYCOCHCERUS 145 



a nearly complete left ilium, acetabulum, and ischium, with a right acetabulum and part of the pubis. 

 This pelvis does not differ in essential respects from that of the John Day E-poreodon, except in size. 

 The length from the anterior margin of the acetabulum to the end of the ilium is approximately 

 132 mm. The diameter of the acetabulum is 40 mm. The maximum diameter across the pelvis, 

 measured from the external edges at the acetabuli, is approximately 157 mm. The pubic symphysis 

 is not less than 60 mm. and may have been somewhat greater. The length of the ischium is 79 mm., 

 exclusive of the tip. This pelvis belonged to an old adult. 



Discussion: In the list of synonyms Merycochoerus temporalis Bettany is intentionally placed 

 at the end. Cope in 1884 was the first to recognize the very close similarity between this species 

 and P. superbus. There are some minor differences between the types of both, but they do not 

 appear to be of fundamental specific value, especially when this group shows so much variation. 



The holotype, Cat. No. 3298 W.M. (Figs. 103-105), is of nearly the same size but has a 

 somewhat shorter molar series. The skull lacks the muzzle and part of the superior cranial region. 



Since this species has been subjected to so many changes in its classification, it is pertinent briefly 

 to review its history. The attention of paleontologists was first directed to Oregon in 1870 when 

 Dr. Leidy reported on a collection of fossils sent to the Smithsonian Institution by the Rev. Thomas 

 Condon, of Dalles City, Oregon. These fossils, collected by Condon, were the first ever to be sent 

 east from the John Day Basin in Oregon. The type specimens of P. superbus were in this collection, 

 and in the same year Leidy described the species as Oreodon superbus. 



Marsh placed this species under the genus Eporeodon, which he established in 1 875. He based 

 his classification on the presence of large bulls; and on the large size of the animal. In 1879 Cope 

 assigned the species to Eucrotaphus, giving no reason therefor, while in 1884 he referred it to the 

 genus Merycochoerus of Leidy. Douglass in 1901 proposed the new genus Promerycochcerus, with 

 P. superbus as the genotype. In the same year Matthew had arrived at the same conclusion as 

 Douglass, that M. superbus (as it was then named) did not belong in Merycochcerus. Almost simul- 

 taneously with Douglass, but somewhat later in 1901, he proposed the generic name Paracotylops 

 for the reception of this species and made the latter the genotype. Douglass' name therefore ante- 

 dates Matthew's and is valid. 



Promerycochoerus thomsoni Loomis 1924 

 Figs. 106-107; PI. XIX; PI. XX, fig. 1 



Original Reference: Miocene oreodonts in the American Museum. Bull. Amer. Mus. Nat. Hist., 

 LI, Art. 1, pp. 22-23, figs. 10-11. 



Type Localities: Ten miles southwest of Eagle Nest Butte, Pine Ridge (HT), and four miles below 

 Post Office, Porcupine Creek (PT), both in South Dakota. 



Geologic Horizon: Lower Miocene (lower Rosebud). 



Types: Holotype, Cat. No. 13819 A.M.N.H., skull of a male, according to Loomis. The paratype, Cat. 

 No. 12948 A.M.N.H., is, according to the same authority, the skull of a female. He designates skulls bearing Cat. 

 Nos. 13818, 12944, and 12951 A.M.N.H., as of the male type. Named for Albert Thomson, collector of 

 the holotype. 



Specific Characters: Holotype: The skull represents the largest Rosebud species. It is of 

 about the size of P. montanus grandis and P. chelydra latidens. The maximum zygomatic expansion 

 is at the glenoid surface. The malar is of medium depth below the orbit, and there is a convexity 

 forward from the anterior zygomatic pedicle to within a short distance of the maxillonasal notch. 

 The squamous portion of the arch is vertically narrow and reaches anteriorly to beneath the post- 

 orbital bar, whence it sweeps first downward and then gradually upward to the crest, which lies in a 

 plane just above the supraorbital margin. The crest is above the base of the paroccipital process. 

 The unreduced nasals extend forward to a point nearly above the incisor margin and are widest at 

 the maxillonasal notch, gradually decreasing in width aft to their pointed posterior terminations, well 



