36 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 







the vertebrae and limb-bones. This appearance of elongation is due to 

 the slenderness of the rostrum and mandible and to the absence of that 

 inflation of the whole frontal region, which is so characteristic of the 

 modern genus. Other differences are the well-defined temporal fossae and 

 the suborbital plate descending from the jugal in Stegotherium. In the 

 vertebrae of the neck and trunk there are no differences that call for par- 

 ticular comment, but the tail of the fossil was almost certainly consider- 

 ably shorter. At all events, the individual caudal vertebrae are shorter 

 and much heavier, while the transverse processes are much broader, 

 leaving less space between those of the successive vertebrae. It is in the 

 dorsal, rather than in the side view, that the difference between the two 

 genera in the character of the caudals is most apparent. The scapula of 

 Stegotherium is smaller, more rounded and of a different shape from that 

 of Tatii, and the pelvis is distinctly heavier, with smaller sacro-sciatic and 

 obturator foramina. The limbs and feet, so far as they are known in the 

 fossil, are very much alike in both genera although they are distinctly 

 heavier in the former. 



Systematic Position. The systematic position of Stegotherium seems to 

 be sufficiently clear ; it is a representative of an entirely extinct line, which 

 has no descendants in the modern fauna. The extreme reduction of the 

 teeth, the elongation of the rostrum, the length and slenderness of the 

 mandible (which has a superficial likeness to that of the anteaters), are 

 all specializations which find no parallel among the existing armadillos. 

 The carapace, as a whole, and the form and markings of the individual 

 scutes are also quite unlike those of any living member of the order. On 

 the other hand, in all parts of the skull and skeleton there is an unmis- 

 takable resemblance to Tatu; the correspondences between the two genera 

 are so many and so close, that they cannot be regarded as accidental, or 

 due to a parallel development. Evidently, Stegotlieriutn is a side-branch 

 of the same stock as that which has terminated in Tatu and, doubtless, a 

 common ancestor of the two lines will eventually be discovered in some 

 of the formations which are more ancient than the Santa Cruz beds. 



Ameghino has constructed a special family for the reception of this 

 genus ('94^, 179), but though this course may eventually be necessary, it 

 does not appear to be called for, so far as our present knowledge extends. 

 It is true that the significance attached to the family is very different 

 among various systematic writers, but palaeontological usage is approx- 



