THE VOYAGE OF THE BEAGLE 95 



The remains at Punta Alta were embedded in stratified 

 gravel and reddish mud, just such as the sea might now wash 

 up on a shallow bank. They were associated with twenty- 

 three species of shells, of which thirteen are recent and four 

 others very closely related to recent forms. 1 From the bones 

 of the Scelidotherium, including even the knee-cap, being 

 intombed in their proper relative positions, and from the 

 osseous armour of the great armadillo-like animal being so 

 well preserved, together with the bones of one of its legs, we 

 may feel assured that these remains were fresh and united by 

 their ligaments, when deposited in the gravel together with 

 the shells. 3 Hence we have good evidence that the above 

 enumerated gigantic quadrupeds, more different from those 

 of the present day than the oldest of the tertiary quadru- 

 peds of Europe, lived whilst the sea was peopled with most 

 of its present inhabitants; and we have confirmed that re- 

 markable law so often insisted on by Mr. Lyell, namely, that 

 the " longevity of the species in the mammalia is upon the 

 whole inferior to that of the testacea." 3 



The great size of the bones of the Megatheroid animals, 

 including the Megatherium, Megalonyx, Scelidotherium, and 

 Mylodon, is truly wonderful. The habits of life of these 

 animals were a complete puzzle to naturalists, until Professor 

 Owen* solved the problem with remarkable ingenuity. The 

 teeth indicate, by their simple structure, that these Mega- 

 theroid animals lived on vegetable food, and probably on the 

 leaves and small twigs of trees ; their ponderous forms and 

 great strong curved claws seem so little adapted for locomo- 

 tion, that some eminent naturalists have actually believed, 

 that, like the sloths, to which they are intimately related, 

 they subsisted by climbing back downwards on trees, and 

 feeding on the leaves. It was a bold, not to say preposterous, 



1 Since this was written, M. Alcide d'Orbigny has examined these shells, 

 and pronounces them all to be recent. 



* M. Aug. Bravard has described, in a Spanish work (' Observaciones 

 Geologicas, 1857), this district, and he believes that the bones of thf 

 extinct mammals were washed out of the underlying Pampean deposit, 

 and subsequently became embedded with the still existing shells; but I 

 am not convinced by his remarks. M. Bravard believes that the whole 

 enormous Pampean deposit is a sub-aerial formation, like sand-dunes: 

 this seems to me to be an untenable doctrine. 



3 Principles of Geology, vol. iv. p. 40. 



*This theory was first developed in the Zoology of the Voyage of the 

 Beagle, and subsequently in Professor Owen's Memoir on Mylodon robustus. 



