LEPTAUCHENIA 239 



Leptauchenia minora Schlaikjer 1935 

 PL XXXVI, fig. 4 



Original Reference: Contributions to the stratigraphy and paleontology of the Goshen Hole area, 

 Wyoming. IV. New vertebrates and the stratigraphy of the Oligocene and early Miocene. Bull. Mus. Comp. 

 Zool., LXXVI, pp. 119, 125, 164-165, 167, 168, pi. 41, fig. 5. 



Type Locality: NW %, Sec. 36, T. 20 N., R. 62 W., Goshen County, Wyoming. 



Geologic Horizon: Lower Miocene (lower Harrison). Approximately 200 feet above the Brule-lower 

 Harrison contact. 



Type: Holotype, Cat. No. 2841 M.C.Z., palate of young individual with I 3 , P\ DP 24 , and M 1 " 2 . Col- 

 lected by E. M. Schlaikjer, 1932. 



Specific Characters: It is always very unsatisfactory to base species on submature specimens, 

 such as this individual. Schlaikjer considers this form to be the smallest so far described, or about a 

 fifth smaller than L. nitida. In my opinion, based on the size of the molars and allowing for the 

 normal growth of the skull, it is about the size of L. decora. The palate is relatively narrow, as 

 we would expect, but even so it is wider than in L. nitida. The alveolar portion of the premaxil- 

 lary is more reduced than in the other species in this genus. 



Dentition: The molars are transversely compressed and long, differing markedly from those in 

 L. nitida and much more like those in L. decora. However, in the latter species the two diameters 

 are nearly the same, whereas in L. minora they are longer than wide. The development of the 

 styles is not greatly marked, as it is in L. major, but is very similar to that in L. decora. The 

 deciduous premolars are crowded, with the first two overlapping. The canines are small and the 

 incisors very small. 



Discussion: In all of the comparable parts I believe that L. minora is closer to L. decora than 

 to L. nitida as considered by Schlaikjer. The skull is somewhat smaller, as would be expected in an 

 immature individual. The molars, both in size and pattern, are very close to those of L. decora. In 

 fact, I should not hesitate to refer this species to L. decora, were it not for certain characters listed 

 below, and I consider it to be a derivative of the latter species or a branch from the L. decora line. 



The differentiating characters, both from L. decora and from the other species in this genus, 

 are: 



1. The lower Miocene age, which makes it the last known form of the genus. 



2. The reduction of the premaxillas and the size of the incisors. 



3. The crowded, and in some cases overlapping, premolars, although it must be borne in mind 

 that these teeth are deciduous and that their position might be somewhat altered later in life. 



Items 2 and 3 may well be considered specializations in the Miocene and could more easily have 

 been brought about in the L. decora line than in that of L. nitida, with its broad molars, well- 

 developed metastyle on M 3 , and prominent mesostyle. 



Leptauchenia nitida Leidy 1869 

 PI. XXXVI, figs. 1-3 



Original Reference: The extinct mammalian fauna of Dakota and Nebraska. Jour. Acad. Nat. Sci. 

 Phila. (2), VII, pp. 129-131, 381, pi. XII, figs. 21, 22. 



Type Locality: White Earth Creek, a tributary of White River, South Dakota. 



Other Localities: Pumpkin Creek, Scotts Bluff, near Fort Mitchell, and along a part of the White 

 River — all in Nebraska. 



Geologic Horizon: Upper Oligocene (upper Brule). 



Types: Holotype, Cat. No. 10870 A.N.S.P., badly damaged skull and other fragmentary parts of skeleton. 

 Collected by Dr. Hayden in 1866. Plesiotype, Cat. No. 10122 Y.P.M., fairly well-preserved skull, lacking both 

 rami and incisor border, as well as parts of zygomata. 



