322 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



In 1873 Leidy named this quadruped P. major, in 

 reference to its larger size as compared with P. palu- 

 dosus, but he was unable to characterize it fuUy. 



At least six rudimentary new characters, or recti- 

 gradations, may now be observed in the grinding teeth 

 alone of this mutation, or subspecific stage — so much 

 for numerical change. The quantitative or propor- 

 tional changes (allometrons) are equally significant of 

 progressive evolution. 



Type and neotype. — Finding it impossible to define 

 this species from Leidy's type specimen, which con- 

 sists of an incomplete and abnormal fragment of a 

 ramus only, a neotype jaw and skull were selected by 

 Osborn from the same geologic level — namely, Am. 

 Mus. 12181 and 12182, from middle Cottonwood 

 Creek, level B 3 in the Bridger Basin. From these 

 specimens discovered by the American Museum expe- 

 ditions the species is defined as above. In continua- 

 tion of the systematic description above, P. major may 

 be clearly distinguished as an important early stage of 

 evolution, successive to P. paludosus. 



Materials. — This species is represented by Leidy's 

 pathologic and fragmentary type ramus (Philadelphia 

 Acad. Nat. Sci. collection, fig. 89) and by six referred 

 specimens in the American Museum from levels B 2 

 and B 3 of the Bridger Basin, as follows: A crushed 

 but finely preserved skull (Am. Mus. 12182), probably 

 belonging with the mandibular ramus (Am. Mus. 

 12181), both from Cottonwood Creek, Bridger Basin, 

 level B 3; a stiU finer specimen (Am. Mus. 13116), 

 from middle Cottonwood Creek, level Bridger B 3; a 

 skuU (toothless) and excellent limb bones (Princeton 

 Mus. 10276); an imperfect palate from Smiths Fork, 

 probably from level B 3 of the Bridger Basin; lower 

 jaws (Am. Mus. 12183) from middle Cottonwood 

 Creek, level Bridger B 3; a fine set of lower teeth 

 (Am. Mus. 12165) from the same locality, level 

 Bridger B 2; fine jaws (Am. Mus. 5101), locality and 

 level unknown. The measurements of the jaws 

 indicated above agree approximately with the few 

 measurements that may be taken from Leidy's very 

 imperfect type, and there is consequently little doubt 

 about the final identification of this species, which, like 

 P. paludosus, has been confused with species belonging 

 to higher stages and higher geologic levels. 



Specific cJiaracfers of type. — The only specific char- 

 acters that can be drawn from the fragmentary type 

 specimen (fig. 89) are the measurements of the lower 

 jaw (97 mm. below ms) and the length of the inferior 

 molar series (mi_3, 115 mm.). 



P. major can not, however, be distinguished specifi- 

 cally by characters taken from the type, such as the 

 length of the true molar series or the depth of the 

 ramus behind ms, because specimens of Palaeosyops 

 leidyi having the same measurements are found at 

 higher levels. It must therefore be distinguished by 

 the characters of the neotype specimens found at the 

 same geologic level as the type. 



Characters of neotype jaw. — The jaw (Am. Mus. 

 12181, fig. 268, C), from Bridger level B 3, middle of 

 Cottonwood Creek, is taken as a neotype, although it 

 belongs to a young adult or a female and is somewhat 

 less robust than the type. This jaw was found near 

 the skull (Am. Mus. 12182) and may belong to it. 

 It affords, however, the following distinctive characters 

 as compared with the referred jaws of P. paludosus: 

 Ps-ms 164 millimeters; p2 with rudimentary para- 

 conid, metastylid fold, and subcrescentic hypoconid 

 (characters all of which are wanting in P. paludosus) ; 

 Pa with distinct paraconid, very rudimentary meta- 

 conid, with metastylid fold subcrescentic and elevated 

 hypoconid; p4 with broadly prominent meta^'.onid, 

 metastylid fold, hypoconid low, broad, and relatively 

 elevated. More in detail, in p2 we see a tooth slightly 

 more progressive than that of P. paludosus in the 

 following respects, as shown in Plate LXII: It exhibits 

 a very rudimentary paraconid and rudimentary 

 metastylid fold and the beginning of a hypoconid 

 crescent, yet these rectigradations are in their very 

 inception. In pa the paraconid, metastylid fold, and 

 hypoconid crescents are accompanied by the ento- 

 conid in its most rudimentary form. In p^ in the 

 unworn condition (Am. Mus. 12165) we see a distinct 

 entoconid and a relatively more elevated hypoconid 

 than in P. paludosus. P. major is therefore dis- 

 tinguished as a mutation or higher stage than P. 

 paludosus by a number of rudimentary cusplets on 

 P2_4 and by the general progress of these teeth toward 

 the molar form. Similarly, in the molar teeth, 

 paraconids, striations on the sides, ridges within the 

 crescents, and festoonings of the external cingulum 

 seem more clearly defined, as well as the entostylids. 

 A very distinctive character also is the hollowing out 

 or concavity of the base of the coronoid process 

 behind m.3, not observed in P. paludosus; the free 

 portion of the coronoid process is still quite high and 

 recurved, not having assumed the triangular form 

 seen in P. leidyi; the thickening of the lower borders 

 of the rami now extends back below the first molar. 



The characters of the jaw of P. major are also 

 exhibited in Am. Mus. 12183 and 5101. They are 

 distinguished by the following principal features: 

 (1) The decided curvature of the lower border; (2) the 

 posterior thickening of the symphysis (ap. 89 to 103 

 mm.); (3) the depth of the ramus behuid ma (86 mm., 

 cotype, female; 96, type, male; 97, Am. Mus. 12183); 

 (4) the slight reduction of the free portion of the 

 coronoid process; (5) the deep excavation of the ante- 

 rior border at the base of the coronoid process. 



Characters of the neotype sTcuU. — The fine skull. 

 Am. Mus. 12182 (figs. 272, 279), from level B 3 of the 

 Bridger Basin, top of Grizzly Buttes, may also be 

 taken as a neotype and possibly belongs with the neo- 

 type jaw above described. It exhibits the following 

 characters, which are well displayed in Plates LVIII, 

 LXII: Superior teeth, p^-m', 147 millimeters; no meso- 

 styles thus far observed on p^ very faint shadow 

 rudiment of a mesostyle on p*, cingulum not completely 



