MEGATHERIOIDS. 333 



MEGATHERIOIDS. 



138. The larger leaf-devouring species of the order Bruta, 

 being too bulky to obtain their food by climbing, were compensated 

 by such colossal proportions and Herculean strength as enabled 

 them to uproot and prostrate the trees on which they fed ; certain 

 toes on each foot were modified for support and progression of the 

 body by hoofs on level ground ; all the known species had complete 

 clavicles, closed zygomatic arches, and a powerful tail as long 

 as the hind-legs, ancilliary to the support of the enormous hinder 

 parts. Every member of this most extraordinary family of quad- 

 rupeds, which was peculiar to the American continents, is now 

 extinct ; their teeth, which governed their diet, closely resembled 

 those of their nearest existing congeners, the Sloths. 



Megalonyx. — The teeth of the species of this genus correspond 

 most nearly, in form, with those of the existing Sloths, and, in 

 their relative size, with those of the Ai, there being no large an- 

 terior laniiform molar, at least, in the lower jaw. Here, on the 

 contrary, the first tooth is the smallest : the second and third teeth 

 are laterally compressed, presenting an ovate transverse section, 

 with the great end turned forwards : the form of the last tooth 

 of the lower jaw, which appears from the mutilated socket in the 

 jaw under consideration, to have been the largest, is not known(I). 

 The tooth (PI. 80, fig. 6), ascribed by Cuvier to the Megalonyx, 

 presents a somewhat irregular, elliptical, transverse section ; and, 

 like those in the lower jaw, has the grinding surface hollowed out 

 in the middle. A tooth (PI. 80, fig. 7), found with certain bones 

 of a Megalonyx in a cavern in Kentucky, presents, in transverse 

 section, a longer and narrower ellipse than the tooth described by 

 Cuvier : there is, also, an irregularity of one side of the ellipse ; 

 the middle prominence of that side which is formed by a longitudi- 

 nal ridge, being stronger, and having a shght concavity or channel 

 on each side : it may probably be, as Dr. Harlan, who has 

 described these interesting remains, conjectures, an upper molar 



(1) See my description of the Fossil Mammalia in the Zoology of the Voj^age of the 

 Beagle, 4to. p. 99, PI. xxix. 



