510 



THE MAMMALIA OF THE UINTA FORMATION. 



DiAG. 2. — Amynodon iniermeiHiis. Side view of the anterior por 

 tion of tlie skull. X \. 



anterior premolar region. The anterior nai'es were apparently widely open. The 



p r e m a X i 1 1 a r i e s are rather nar- 

 row above and spread inferiorly, 

 rounding and arching forwards into 

 the broad incisive border ; the rela- 

 tions of these bones in Metamynoclon 

 indicate that they had a deep area of 

 union in front, contrasting strongly 

 with the separate slender premaxillfe 

 of Aceralherium. The m a 1 a r pro- 

 jects widely below the orbit which is immediately above the second molar and the 

 maxillaries are deeply depressed and incurved in front of the antorbital ridge. 



The upper and posterior regions of the skull are entirely wanting in this speci- 

 men, and have been fully described in the E. M. Museum Bulletin upon the skull of 

 A. (OrtJiocynodou) antiqims. 



The lielations of the Amynodontidce. 



The Washakie sjiecics, both in structure and time, is the most primitive form, as 

 indicated by the complete dentition and the perfectly erect position of the canines. 

 Then follows the A. advenns from the Uinta with small erect canines and the reduc- 

 tion of one premolar, otherwise very similar in size and dentition to the foregoing. 

 The A. intermed.ius, while retaining the rudiments of the first premolar, which were 

 probably lost in fully adult specimens, shows a vei-y decided transition towai'ds Me- 

 tamynodon in the enlargement, shape and procumbent position of the canines, also in 

 the broadening of the snout and compression of the antorbital region. It is sing- 

 ular to note how little i)rogress the premolars of Melamynodon show ; the second pre- 

 molar is like the third, but in none are the posterior crests very prominent. 



Pliyloyenetic Position of Aynynodon. 



The discovery of Amynodon.^ with its full complement of teeth and markedly 

 rhinocerotic molar pattern, naturally led Pi'of Marsh to suppose he had found the 

 long-sought Eocene representative of the true rhinoceroses.* This opinion has been 

 adopted by every one. But the discovery of Metamynodon, which is certainly far from 

 the I'hinoceros line and is an undoubted successor to these Eocene forms, directs atten- 

 tion to a number of developmental features which suggest an entirely distinct supposi- 



*IntroiUiclion and Siiecossiun of Vcrlelirale Life in Anuiica, n. ;iO. 



