142 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



T. garrettorum, is considerably taller and stouter than the llama, to which 

 it bears some resemblance in general proportions. The head is rather large, 

 but low and the much shortened nasals and immense, tapir-like anterior 

 nares give it a highly peculiar and characteristic appearance. The long, 

 slender rostrum and mandible, and the conical, sharp-pointed and slightly 

 recurved anterior teeth are almost reptilian in effect. The long neck and 

 limbs and the rather short trunk and very short tail are the especial 

 features which recall the proportions of the llamas, but the much shorter 

 tridactyl feet and separate metapodials form a striking difference from any 

 of the existing Tylopoda. An unusual character is to be found in the 

 relative lengths of the limb-segments ; the upper arm is short and the 

 fore-arm very long, while in the hind limb this proportion is reversed, the 

 thigh being long and the leg short. 



The skeleton of Macranchenia bears an unmistakable resemblance to 

 that of Theosodon, but, in addition to the numerous differences of detail 

 described in the preceding pages, there are some obvious differences of 

 proportion. MacraucJienia was a much larger animal than the Santa Cruz 

 genus and has relatively longer limbs, with which the elongation of the 

 neck has not kept pace. The skull, in adaptation to the growth of the 

 proboscis, has become quite different in appearance and the trunk is prob- 

 ably shortened, though this is not altogether certain. At all events, the 

 trunk-vertebrae are proportionately smaller and have more slender spines, 

 which are more inclined in the anterior part of the thoracic region and 

 more erect in the lumbar. The scapula is much narrower than in The- 

 osodon and the acromion and metacromion are far less developed, while 

 the pelvis is shorter, is set more nearly vertical to the axis of the spinal 

 column and has the iliac plates much more strongly everted. These dif- 

 ferences are just what we should expect to find between ancestor and 

 descendant and, so far as present knowledge is concerned, there is no 

 reason why we should not regard Theosodon as directly ancestral to the 

 Pampean MacraucJienia. 



Synonymy. — The isolated position of Theosodon in the Santa Cruz 

 fauna is such that there has been little difference of opinion as to the 

 proper nomenclature. Lydekker ('93, 65) has made this genus a synonym 

 of Oxyodontotheriimi from the much later Parana beds, but with this view 

 I am quite unable to agree, on account of the differences in tooth-structure, 

 not to mention the highly probable differences in the skull. Ameghino 



