SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. 



Perissodactyla. 



Upper molars with conules early- 

 fusing into two transverse crests. 



Lower molars without pillar in pos- 

 terior crescent. 



Alisphenoid canal present. 



Tympanic usually forming a bulla. 



Odontoid process of axis spout- 

 shaped in long-necked genera, 



Zygapophyses of posterior thoracic 

 and lumbar vertebrae with plane 

 faces (except in horses). 



Mesosternal segments broad and 

 depressed. 



Scapula without acromion (except 

 in early horses) or metacromion. 



Ulna greatly reduced in genera with 

 enlarged digit III. 



Carpus strongly interlocking, with 

 scaphoid resting on magnum and 

 lunar on unciform. 



Fibula not articulating with cal- 

 caneum. 



Distal end of astragalus flat, articu- 

 lating with navicular and cuboid. 



Digital reduction adaptive. 



LiTOPTERNA. 



Upper molars imperfectly lopho- 

 dont, posterior crest not formed. 



Lower molars with pillar in pos- 

 terior crescent (sometimes re- 

 duced). 



No alisphenoid canal. 



Tympanic scale-like. 



Odontoid process always peg-like. 



Zygapophyses of posterior thoracic 

 and lumbar vertebrae semicylin- 

 drical. 



Mesosternal segments mostly nar- 

 row and compressed. 



Scapula with acromion and meta- 

 cromion largely developed. 



Ulna little reduced and proximally 

 larger than radius. 



Carpus semi-taxeopod, with sca- 

 phoid resting on magnum, but 

 lunar not touching unciform. 



Fibula articulating with calcaneum. 



Distal end of astragalus depressed- 

 convex, articulating with navicu- 

 lar only. 



Digital reduction inadaptive. 



To my mind, the preponderance of evidence is thus decidedly in favor 

 of the view that the Perissodactyla and Litopterna are no more closely 

 related than two ungulate orders must necessarily be (if the monophyletic 

 origin of the hoofed animals be a fact) and that resemblances between 

 them are due to parallelism and not to genetic affinity. The primitive 

 features of the Litopterna, such as the semi-taxeopod carpus and tarsus, 

 extensive articulation between the fibula and calcaneum, and the inadap- 

 tive method of digital reduction, are all as distinctly marked in the highly 



