50 



(iUIDE TO THE FOSSIL MAMMALS AND BIRDS. 



Pier-cases 



20, 21. 



Table- case 



11. 



Pier-case 

 20. 



arrauged in three sub-orders, are nearly all different from 

 any Ibund elsewhere. The South American llamas, deer, 

 peccaries, tapirs, extinct horses and mastodons, of course, are 

 not indigenous, but passed south over the newly emerged 

 isthmus of Panama or other land-l)ridge at the l)eginning of 

 the Pliocene period. 



Some of the earliest knuwn South American hoofed 

 mammals, such as Ptirothcrium, are very little different from 

 the Amblypoda and Condylarthra (jf the northern hemisphere. 

 I'laster casts of jaws, teeth, and feet of Pyrothcrium from 

 Patagonia are exhibited in Pier-case 20. The later forms, 

 however, are peculiar in the folding and complication of 

 their often persistently-growing teeth ; also in the structure 



Fig. 40. — Skeleton of Phenacochis primaivus, as now mounted in the 

 American Museum of Natural History, New York. 



Pier-cases of tlieir feet when they begin to become plain-dwellers and 

 Case T iiii'iiic the rhinoceroses and horses of the rest of the world. 

 Toxodon (Fig. 41) is an especially j-emarkable l)east with 

 ever-growing powerful cutting and grinding teeth, well seen 

 in actual specimens in Pier-case 21. A plaster cast of a 

 reconstructed skeleton of this large animal from the Pampa 

 of the Argentine Eepublic, now in the La Plata Museum, is 

 mounted in a special Case marked T. When alive it must 

 have been shaped much like the contemporaneous rodents 

 and giant armadillos. It was preceded in time by Ncsodon 

 and other smaller kinds of which remains are shown in 

 Table-case 11. Macrcmclienia, also fi-oni the Pampa Forma- 

 tion, was a large animal shaped like a llama, Ijut with thiee 



