Exploration for the Remains of Giant 

 Ground Sloths in Panama 



By C. Lewis Gazin 



Curator, Division of Vertebrate Paleontology 



United States National Museum 



Smithsonian Institution 



[With 8 plates] 



Undoubtedly the giant ground sloths of prehistoric time in the 

 Western Hemisphere had no peer among mammals of great bulk in 

 their grotesque unwieldiness and sluggishness of habit. They rivaled 

 the mammoth and mastodon in body size (pi. 1) but, of course, did not 

 otherwise resemble them, and certainly could not have kept pace in 

 their movements. It would seem impossible that they could have 

 survived and evolved in any reasonably competitive atmosphere or 

 environment. Clearly, the explanation is that together with other 

 edentates — the armadillos, glyptodons, true anteaters, and the some- 

 what more closely related slow-moving tree sloths of tropical 

 America — they underwent their principal or later development and 

 specialization in South America, isolated from the more highly com- 

 petitive herbivores and especially the more aggressive predators, such 

 as the wolves, pumas, and saber-tooth cats of the north. 



About the beginning of the ice age or Pleistocene time, the northern 

 and southern continents became joined by a land bridge, probably at 

 about the present Isthmus of Panama, or possibly nearer Colombia, 

 permitting rather extensive migrations of land animals. At that time 

 many of the more progressive northern types such as the horse, llama 

 and related cameloids, mastodon, and various carnivores and rodents 

 invaded South America, whereas opossums, porcupines, capybaras, 

 toxodons, and several kinds of edentates, including ground sloths, 

 succeeded in making their way north. Ground sloths, glyptodons 

 with their turtlelike armor, and strange rhinoceroslike toxodons, 

 however, did not survive the Pleistocene. Toxodons did not get north 

 of Central America but certain of the smaller kinds of ground sloths 

 established themselves as far north as Pennsylvania and Idaho. One 

 of these, Megalonyx, from a cave in West Virginia, was first described 



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