METOREODON 2 1 1 



strength to compensate for the posterior position of the anterior nares, but they do not seem to be 

 proportionally longer. The face is, however, longer (including the orbits) than the remainder of the 

 skull. The posterior part has been foreshortened rather than the face lengthened, in my judgment, 

 and this is the general rule throughout this family, as many genera will testify. 



Matthew and Cook (1909, p. 395) regarded an isolated M 3 , figured by Leidy (1869, pi. X, 

 fig. 5) as Merycochaerus, as wholly different from the M 3 of that genus and especially close to 

 Metoreodon. I am in accord with the view that it is not typical of Merycochaerus frofrius. It has 

 a larger metastyle and a swelling, or accessory cusp, on the posterior side of the hypocone. Accessory 

 tubercles on the molars of merycoidodonts are not unusual and may be considered as individual varia- 

 tions. I have seen many examples of this in different species, perfectly normal otherwise, which 

 apparently do not lead to a permanent variation. The enlarged metastyle is not more like Metore- 

 odon than Merycochaerus. The parastyle and mesostyle on this M 3 are rolled forward, as in Mery- 

 cochaerus, while in Metoreodon they are at right angles to the tooth and very much thinner in 



Fig. 153. — Metoreodon frojectus Matthew and Cook. Superior dentition. PLT. Cat. No. 6-7-11-13 N.S.M. 



2/3 nat. size. 



proportion. The size of this molar is about the same as in Merycochaerus but is larger than the 

 corresponding tooth of any known species of Metoreodon. Therefore it is my opinion that this 

 tooth is not referable to the latter genus but does belong to Merycochaerus and probably to 

 M. frofrius, to which it is nearest in size. 



Barbour and Cook (1917) thought that the large antorbital pit is probably largely due to the 

 development of the muscles which control the flexure of the snout. It may be that part of this 

 apparently large pit is part of the facial vacuity, but unfortunately the bone is broken away in the 

 corresponding area on both sides. However that may be, I believe that the pit is for the accommo- 

 dation of nasal diverticuli, and that the origin of the snout and lip muscles is above, below, and in 

 advance of this fossa. The increase in depth of the pit in later merycoidodonts may be correlated 

 with the increase in their keenness of sense of smell to compensate for their lack of adequate means 

 of defense. They had no horns, the canine teeth diminished in proportionate size, they had only small 

 hoofs, and in general all that they had for individual protection was the senses of sight and smell 

 and their fleetness of foot. The latter developed in only a few genera, hence the sense of smell was 

 undoubtedly of paramount importance to this whole great group. 



Recently Stirton sent to me for examination two skulls, a maxillary fragment, and the anterior 

 part of a left ramus of oreodonts, all from the Pliocene. I consider them all referable to Metoreodon 

 and, provisionally, to M. frojectus. The reasons for qualifying my specific determination are: first, 

 one skull, Cat. No. 32310 U.C.M., the maxillary fragment, Cat. No. 32331 U.C.M., and the frag- 

 mentary left ramus are all of immature individuals, with M 3 not erupted and with the premolars 

 deciduous; second, the other skull, Cat. No. 32841 U.C.M., is that of an individual so old that the 

 teeth are worn down nearly to the roots. No one of the specimens displays the characters of a 

 typical M. frojectus, but each shows more of the diagnostic conditions of that species than of any 

 other. 



The immature specimens were collected in Big Spring Canyon, South Dakota, about 60 miles 

 west of the Rosebud Agency, while the skull of the older individual came from Schliegels Creek, 

 Cherry County, Nebraska. The former are lower Pliocene in age and the latter is probably Valen- 

 tine, lower to middle Pliocene. 



