LEPTAUCHENIA 235 



Sinclair pointed out the general resemblance between the skeleton of this genus and that of 

 Phenacocoslus, which he considered to be related to both Leptauchenia and Cyclopidius. Loomis, 

 Leidy, and Scott have pointed out the similarity of skeletal structure to that of Merychyus except for 

 five toes on the manus, and the similar teeth. Loomis thinks that these two lines, Merychyus and 

 Leptauchenia, branched off from the same stock in the lower Oligocene, perhaps from the light- 

 limbed Limnenetes line of the lower Oligocene titanothere beds, but that probably this genus was 

 not the actual ancestor. 



It is a peculiarity of this genus that the tooth pattern becomes obliterated fairly early. Loomis 

 (1924B, p. 14) says: 



When, however, little-worn teeth are studied, it is seen that the upper premolars are shortened by the almost 

 complete suppression of the anterior portion. When such teeth are worn, the median crest appears like the anterior 

 crest, and the tooth seems to stand transversely in the jaw. This peculiar appearance, however, is due to the sup- 

 pression of the anterior basin. Premolar 3 ... has a large posterior crescent which does not unite with the 

 median crest. Premolar 4 in little-worn teeth shows the pit in the anterior external corner. The lower premolars 

 are characterized by the entire lack of crescents and intermediate crests. The fourth premolar is unique in the 

 enormous swelling of the posterior crest, so that this fills the posterior basin. 



I cannot conceive of this genus being a water-living animal, any more than was Cyclopidius. 

 Sinclair says that the slender toes, terminated by tiny hoof-like ungues, are well adapted for running 

 on firm ground. He states further (1910, p. 198): 



The slight development of lower incisors and canines indicates, perhaps, that Leptauchenia was not a grazing 

 animal, for in modern grass feeders, while the upper incisors and canines may be absent, the lower teeth are broad 

 and flat, well adapted to cropping grasses, while in Leptauchenia they are almost cylindrical. 



Schlosser (1886B and 1888) derived the llamas from Leptauchenia. There are certain resem- 

 blances to the Tylopoda, such as the condyle of the lower jaw, but I am confident that any close con- 

 nection between the Merycoidodontida; and the Tylopoda must have been in the remote ancestry of 

 both groups, since which time they have diverged markedly. 



Leidy recognized the superficial resemblance to the skull of Auchenia (llama) and hence his 

 name of Leptauchenia (leptos, small, slender) for the genus. 



Species: 



L. decora Leidy 1 856. Genotype. 



L. major Leidy 1 856. 



L. minora Schlaikjer 1935. 



L. nitida Leidy 1 869. 



Leptauchenia decora Leidy 1856 

 Fig. 6; PI. XXXV; PI. XLVIII, fig. 2 



Original Reference: Notices of remains of extinct Mammalia. Proc. Acad. Nat. Sci. Phila VIII 

 p. 88. 



Type Localities: Cotypes, from the valley of the White River and from Bear Creek, Nebraska; paratypes, 

 from near Eagle Nest Butte, on White River, South Dakota; and plesiotypes, from near Fort Mitchell, North 

 Platte River, and from a location 18 miles west of Harrisburg, Nebraska. 



Other Localities: Crow Buttes, Lawrence Fork, Court House Rock, Scotts Bluff, Omaha Creek, 

 Rattlesnake Butte (near Chadron), and Pumpkin Creek, Nebraska; Spring Creek, near Camp Baker, Montana. 



Geologic Horizons: Upper Oligocene (upper Brule) to lower Miocene (lower Monroe). 



Types: Genocotypes and genoparatypes not differentiated. Cat. Nos. 10875-10940 A.N.S.P., mainly frag- 

 mentary upper and lower jaws, with teeth, and a much damaged skull, collected by Dr. Hayden in 1855. 

 Plesiotypes, Cat. Nos. 101 19 and 10121 Y.P.M., skulls, and Cat. No. 2-26-7-32 SP N.S.M., well-preserved skull 

 with left jaw. 



Specific Characters: The skull is intermediate in size between that of L. major and L. nitida. 

 It is also smaller than in Merycoidodon gracilis, as well as broader, shorter, and lower. The malar is 



