94 



EDENTATA 



ORDER V 



Megalonychinae and Mijlodontinae, and among these the Megalomjchinae are 

 much diversified. These older forms are almost without exception much 

 inferior in size to their Pleistocene relatives. Dermal ossification is not 

 observable in any one of these forms. The dental formula is always f , and 

 the first tooth in both jaws is always canine-like. The skull is distinguished 

 by a long snout and a large brain-case. The trunk and scapula are more 

 like those of Bradypodidae (Choloepus) than of the Pleistocene Gravigrada. 

 The limb bones are always more slender, and the humerus is invariably pro- 

 vided with an entepicondylar foramen. Fusion of the carpals, tarsals or 

 phalanges never occurs. The middle metapodial is, however, much shorter 

 and thicker than the others, but the two outer ones are much less specialised 

 than in the later Gravigrade forms, because the outside of the foot does not 

 rest on the ground. The Miocene Gravigrada approach the Bradypodidae and 

 Myrmecophagidae in exhibiting many similar skeletal structures. 



Subfamily 1. Megatheriinae. 



|- cheek teeth ptrismatic, quadrangular and closely set, the last one somewhat smaller 

 than the rest. The posterior branch of the alveolar canal opens on the inner side of 

 the lower jaw. 



Megatherium Cuv. (Fig. 116). The first complete skeleton was exhumed 

 in 1789 in Argentina, and sent to Madrid. Besides M. americanum Blumb. 



( = M. giganteum Pan- 

 der), other species in 

 the Pleistocene of 

 Argentina, Brazil, 

 Chile, Ecuador, Central 

 America and the 

 southern United States 

 are known. 



Nothr other ium 

 Lydekker {Coelodon 

 Lund). A considerably 

 smaller form than 

 Megatherium. Pleistocene ; Brazil and western United States. 



Neoracanthus, Essonodonthcrium Ameghino. Pleistocene of Argentina. 

 Zamicrus, Promegatherium and Interodon Ameghino. Pliocene of Argentina. 

 Scott considers the Planopsinae (Frepotheriidue Ameghino), from the Upper 

 Miocene of Santa Cruz in Patagonia, and comprising the genera Planops and 

 Prepotherium Amegh., to be ancestral to the Megatheriinae. These are the 

 largest Grar^igrada, found in the Miocene of Santa Cruz. In common with 

 the Megafheriinae they have the massive tail, the elongated ischium and pubis, 

 the short, broad astragalus and a long upper portion of the calcaneum, but 

 lack ridojes on the crowns of the teeth. 



Megiitheriuiii aiiwricanum Blumb. Pampas formation (Pleistocene), 

 Argentina. Superior aspect of lower jaw. Va- (After Owen.) 



Suljfaiuilv 2. Megalonychinak. 



f clieek teeth prismatic, quadrangular or transversely elliptical. The first widely 

 separated from the remaining ones, and canine-like. Hindmost tooth small. The 



