216 INTRODUCTION TO EVOLUTION 



phants and mammoths are characterized by the massive molar structure 

 previously described, by the longitudinal method of molar replacement, by 

 possession of a short, high skull and a short, tuskless lower jaw. We may 

 note in passing the interesting fact that the fetus of the elephant has a long 

 lower jaw. As development continues the jaw becomes relatively shorter 

 (de Beer, 1958). Here is another example of recapitulation (pp. 50-51). 

 Probably if we could but learn of them we should find that the fetuses of 

 all proboscideans had long lower jaws. The adult Moeritherium retained 

 the jaw in about its fetal proportions. In some of the proboscideans (e.g., 

 Gomphotherium) the adult jaw became still further elongated, while in 

 others it became relatively shorter. 



During Pleistocene times a variety of mammoths ranged widely over the 

 earth, including regions with climates not suitable for the two modern ele- 

 phants. Thus the woolly mammoth wandered into arctic regions. This 

 mammoth is perhaps the most completely known of all prehistoric mam- 

 mals, owing to the happy fact that complete carcasses have been found in 

 the permanently frozen gravels of northern Siberia. Thus the "soft parts" 

 usually unavailable for study in fossil animals have been preserved along 

 with the bones. Thanks to this fortunate preservation, we know that this 

 mammoth was covered with coarse, dark brown hair, having a maximum 

 length of 20 inches, and with a dense undercoat of woolly hair about an 

 inch long. The creature has added interest for us because of cave paintings 

 and carvings of it made by our prehistoric relative, Cro-Magnon man 

 (p. 245). Presumably these mammoths served as a source of food for men 

 of the time. 



Although the height of about 9.5 feet attained by the woolly mammoth 

 did not equal the height of large Asiatic elephants today, some other 

 mammoths exceeded the latter. The imperial mammoth, for example, was 

 13.5 feet high at the shoulder. This mammoth and some of its American 

 contemporaries were characterized by extreme spiraling of the tusks. 

 Since the spiral tusks continued to grow throughout life, in some old 

 individuals the tips actually crossed each other, producing a condition in 

 which the tusks were effective neither for digging nor for fighting. 



References and Suggested Readings 



de Beer, G. R. Embryos and Ancestors, 3rd ed. Oxford: Oxford University 



Press, 1958. 

 Camp, C. L., and N. Smith. "Phylogeny and functions of the digital ligaments of 



the horse." University of California, MEMOIRS, 13 ( 1942), 69-123. 



