24 THE MERYCOIDODONTlDyE 



with its short muzzle and pentacuspid brachyselenodont teeth, but the inferior canine is the true 

 canine enlarged into a tusk. Cebochcerus has a short muzzle and caniniform Pi but tetrabunodont 

 molars while Chcerofotamus has a long muzzle, with bunodont teeth and caniniform P,. Diplo- 

 bune bkhobune, and many others have been used for comparison. Many of these European forms 

 became extinct at the close of the Eocene, but in any event they were too specialized to have been 

 ancestral to the American oreodonts. However, it is extremely probable that the European and 

 American genera had a common ancestral stock, inhabiting a north Asiatic area (the Holarctic con- 

 tinent Eria), whose fauna spread southward and westward to give rise to the Old and New World 



Loomis (1925C, p. 589) called attention to the fact that Archceomeryx of the later Eocene of 

 Mongolia is the earliest form which shows in its molar pattern the characters of the modern artio- 

 dactvls and it affords no hint that the molars ever had more than four cusps. The lower first pre- 

 molar is caniniform, and the true canine is incisiform, as they are in all of the known merycoido- 

 donts Archceomeryx is not ancestral to the family under consideration, but in my opinion it indicates 

 that the true ancestors did not have the fifth lobe, or protoconule, and that Protoreodon, possessing 

 the protoconule, is not in the direct line of ancestry. In other words, the true stem stock of the 

 Merycoidodontid* has not yet been discovered. From a study of the brain casts, it is clear that they 

 show a combination of suilline and ruminant characters, but which predominates it is impossible to 



6 The"" skull's of oreodonts and of suids have comparable tusk mechanism, but it is produced in 

 different ways in that in the former the tusks are £ and in the latter c c , the lower tusk in the former 

 being a premolar which has assumed the shape and function of a true canine but bites behind instead 

 of in front of the upper canine. In other characters there is very little similarity between the sku Is 

 of the two groups. The position of the orbits and of the cranium, as well as the shape of the muzzle, 

 is much more suggestive of the tragulines, but here again the oreodonts differ from all of the modern 

 ruminant artiodactyls, and also from the suillines, in the transverse set of cropping incisors in each 

 pair of jaws, resembling more the horses and tapirs in this respect The position of the ok low 

 and above the molars, as in the tragulines and the less specialized selenodonts, in contrast with the 

 posteriorly placed, elevated orbit of the suillines. Again, the muzzle is very much shorter than 

 [hat of suillines or ruminants and differs from both, not only in the aforementioned cropping incisors 

 but in the absence of diastemata behind the lower caniniform premolars and in the very short 

 diastemata behind the superior canines. fi 



Were the oreodonts ruminants? Their remains are found almost exclusively m the ^fine- 

 bedded, uniform material which makes up the greater portion of the Tertiary deposits in the West, 

 wherea they are very scarce or entirely absent in the coarse sandstone lenses river-channel deposits) 

 Td n he fossiliferous sand and gravel deposits (quicksands, pools, etc.) which o ten con am a grea 

 abundance of fossil mammals other than oreodonts. The evidence in general therefore pom s 

 mdubi b y to the conclusion that these oreodonts lived in the open, for the most part avoiding run- 

 rnng water and large bodies of standing water, and that they developed a grazing habit, that is, they 

 b fnged o the plains fauna. If this view is correct, they probably did not ruminate (chew the 

 cud) If they had been in the habit of making frequent trips to the streams, some of them at least 

 would have fallen prey to the carnivores which must have often lain in wait in the copses along nver 

 baTks and near Jter holes, and remains of these oreodonts would have been preserved in the 



Sand Many wrkers, including the present one, have thought that certain characters indicated a semi- 

 aquat co amphibious mode of life for some of the oreodont genera. At present I am not at all 

 mdbed to this view. The elevated auditory meatus and the highly placed orbits were cons.dered 

 o be aquatic adaptions, but, with the exception of the hippopotamus they are not found in truly 

 mphibious animals, such as the tapir, while they are found in the suids, wh ,ch are not amph biou, 

 Verv heavv massive bones and widespreading toes are also characteristic of amphibious animals, but 

 I It i no^ug^tion of these in the oreodonts. The orbits and the auditory meatus are not actu- 

 ally more elevated, but the skulls in these controversial genera are depressed and flatter, and those 



