280 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



711) Cope mistakenly referred to this genus the two 

 species L. ( = Eotitanops) hrownianum. and L. procyo- 

 niiMm. In the same memoir he placed all the Eocene 

 titanotheres in the family "Chalicotheriidae." In his 

 memoir of 1892 Earle correctly considered this animal 

 a probable member of a side line of titanotheres. In 

 1893 Osborn recognized the division as a subfamily — 

 "Lambdotheriinae." In 1897 Osborn mistakenly pro- 

 posed to remove Lamhdotherium from the titanotheres 

 and related it to the Equidae on the ground of its slen- 

 der foot structure. The renewal of the demonstration 

 of its relation to the titanotheres is due to W. K. 

 Gregory. In 1907 Loomis discovered five specimens 

 of this genus in the deposits of Buffalo Basin, one of 

 which he selected as the type of the new species L. 

 primaevum, believing it to represent a stage somewhat 

 more primitive and perhaps geologically older than L. 

 popoagicum. In 1905 and 1909 the American Museum 

 party under Granger finally determined that these 

 animals were geologically contemporaneous with Eoti- 

 tanops but confined to a comparatively narrow geologic 

 zone. 



The principal collectors and the areas in which they 

 worked were as follows: 



1880. E. D. Cope, J. L. Wortman, for American Museum of 

 Natural History; Wind River Basin, Wyo. 



1896. J. L. Wortman, for American Museum of Natural His- 

 tory; Huerfano Park, Colo. 



1905. Walter Granger, for American Museum of Natural His- 

 tory; Wind River Basin, Wyo. 

 F. B. Loomis, for Amherst Museum; Big Horn Basin, 



Wyo. 

 Walter Granger, for American Museum of Natural His- 

 tory; Wind River Basin, Wyo. 



1907. 



1909. 



1916. Walter Granger, for American Museum of Natural His- 

 tory; Huerfano Park, Colo. 



1918. Walter Granger, for American Museum of Natural His- 

 tory; Huerfano Park, Colo. 



Geologic horizons. — The animals found in four ex- 

 posures of the Lamidotherium zone in the Wind River 

 Basin, the Big Horn Basin, the Beaver Divide, and 

 Huerfano Park, each 300 to 400 feet thick, are not 

 separated by marked differentiation or evolution; in 

 all these basins and on all the levels of each formation 

 the lambdotheres, so far as known, are substantially 

 similar in size but differ markedly in the degree of 

 evolution of the third and fourth lower premolar 

 teeth. The range in size is indicated on page 282 . A 

 very striking fact is that the extremes of premolar 

 structure (-fig. 234) were found in animals collected 

 around the great Alkali Creek "red stratum," which is 

 such a conspicuous level mark (fig. 47), many of the 

 specimens being just below the "red stratum," or 50 

 to 100 feet above the base of the Wind River forma- 

 tion. The greater part of the collections have been 

 made within a vertical distance of 200 feet, which 

 would represent time for considerable evolution; but 

 as the stages of evolution do not occur successively in 

 the ascending levels, it does not appear practicable to 

 separate any but the extreme forms as species or 

 mutations, and the systematic order therefore appears 

 as follows: 



Lamhdotherium progressum Osborn (most progressive) . 

 L. popoagicum Cope, L. primaevum Loomis (inter- 

 mediate) . 

 L. priscum Osborn (most primitive). 



Measurements of teeth of Lamhdotherium, in millimeters 



[The numbers are those of specimens in the American Museum of Natural History] 



