FIELD BOOK OF MAMMALS 



Sp ecies and Subspecies of the Genus Antilocapra 



American Pronghom.' — Antilocapra americana americana 



(Ord). 

 As described. Found from the Mexican boundary north- 

 ward, see map, 

 Mexican Pronghom. — Antilocapra americana mexicana Mer- 

 riam. 

 Paler in color, brown with a tinge of ecru or cinnamon, than 

 typical americana. Found only along Mexican boundary 

 and thence southward. 



******* 



"The pronghom is the only antelope in the world with 

 branched or pronged horns and has the unique characteristic 

 among all hollow-homed ruminants of shedding the outer 

 covering of the horns annually. This takes place soon after 

 the rut in November and December in the Yellowstone 

 National Park in northern Wyoming, and elsewhere in the 

 range of the species this time probably varies somewhat with 

 latitude. 



"When the time for shedding arrives the homy sheath 

 gradually loosens and becomes detached from the skin around 

 the base and, following this, from the bony core within. 

 Later the horn falls off, leaving the bony core covered with a 

 blackish skin more or less overgrown with long, coarse hairs, 

 which afterward are gradually lost. A new homy nucleus 

 develops on the tip of the bony core, the homy growth then 

 extending slowly downward until it reaches the base. Gradu- 

 ally thickening and hardening, the homy material grows at the 

 tip until the new horn attains its full development. The horns 

 continue to grow as the animal increases in age until the full 

 size is reached. 



"Both sexes have horns, those on the does being smaller 

 and slenderer than on the bucks. 



''Rump patch. — -Another characteristic of these interesting 

 animals is a conspicuous rump patch composed of white hairs 

 which are longer than those elsewhere on the animal's back. 

 Through developments in the skin muscles the pronghom at 

 times of excitement has the power to erect these white hairs 

 until they stand out stiffly over the rump, forming a great 

 dazzlingly white rosette, like a giant chrysanthemum, which, 

 when the animal is dashing away across the plains in the 

 bright sunlight, is extraordinarily conspicuous. The writer 



536 



