Why Antlers 

 Branched Ou 



by Valerius Geist 



Every large museum of natural history 

 has its collection of ungulate heads, horns, 

 and antlers — mostly donated by nine- 

 teenth-century sportsmen obsessed by 

 such trophies of the hunt. These same in- 

 stitutions amassed fossilized Irish elk 

 antlers and skulls of extinct giant moose 

 and bison. Hoofed mammals have evolved 

 many types of horns: the antlers of deer; 

 the true horns of cattle, sheep, and an- 

 telopes; the false horns of North America's 

 pronghorns; and the hairy, skin-covered 

 horns of giraffes. Several extinct species 

 sported horns of odd architecture. But of 

 what scientific value is this jumble of di- 

 verse heads and horns, ancient and mod- 

 em? What might they tell us about the 

 evolution of hoofed mammals? 



Observing living animals may help an- 

 swer such a question. In December 1961, 

 during a three-year field study of moun- 

 tain goats in the Cassiar Mountains of 

 northern British Columbia, I watched a 

 typical territorial dispute near my cabin. A 

 female mountain goat, her short, sharp 

 horns lowered, rushed a much larger male. 

 The big billy jumped aside, turned away, 

 and hastened down the hill, with the fe- 

 male in pursuit. As he looked back over 

 his shoulder, she jerked her head up 

 sharply, prompting the male to accelerate 

 his departure. I did not see him for the rest 

 of the winter. 



The female had a more difficult time 



with a young billy that was about two or 

 three years old and about her size. When 

 she advanced menacingly, he arched his 

 back into a dominance display, but the fe- 

 male charged nevertheless. A brief, vio- 

 lent fight erupted on the snowy slope as the 

 goats whirled about, thrusting their sharp 

 horns into each other Finally, the younger 

 billy, too, took flight and never returned. 



Such dramas, which follow the mating 

 season in early winter, are part of the 

 mountain goat's biology: dominant fe- 

 males with kids clear out other goats (in- 

 cluding the largest males) from chosen 

 areas of superior habitat, known to scien- 

 tists as "resource territories." The steep, 

 jagged chff near my cabin was regularly 

 swept of snow by strong, warm chinook 

 winds, making it a good place for goats to 

 forage, even after a blizzard. The female's 

 relentless aggression, enforced by her 

 horns, insured that she and her offspring — 

 one by her side, one growing in her 

 uterus — had the food they needed to sur- 

 vive and thrive. 



Mountain goats' short, shghtly curved, 

 needle-sharp horns make ugly wounds 

 that hemorrhage beneath the skin. 

 Wounded goats hobble about for a long 

 time after a fight and give every indication 

 of being hurt. The species' horns seem to 

 have evolved to cause a maximum of pain 

 and to enable them to be quickly with- 

 drawn from the victim's body before they 



Living New World deer are arranged, front to back, 

 from tropical dwarfs with short spikes to caribou and moose that 



evolved giant antlers during the ice ages. The species are (a) 



Andean deer, or guemal, (b) pampas deerfivm South America, 



(c) mazama, one of the brocket deer, (d)pudu, the smallest 



living deerfivm the Andes, (e) white-tailed deer of the 



tropics, (f) marsh deer from South America, (g) mule deer of 



western North America, (h) white-tailed deer of northern 



temperate zones, (i) caribou, or reindeer, which live in 



arctic and alpine areas of both the New and Old World, and {']) 



moose from the subarctic and subalpine regions of the 



Old and New World. 



can become caught and snap the neck of 

 the aggressor. The short, spiky shape of 

 the horns proclaims the species to be one 

 that aggressively defends resource territo- 

 ries — although in this case only the fe- 

 males do the defending. 



Other living animals with similar homs 

 and territorial behavior include the duikers 

 of Africa, dwarf antelopes that inhabit 

 scrub and forest; the httle brocket deer that 

 range from Argentina to Central Mexico; 

 and the Indian nilgai, Asia's largest ante- 

 lope. Fossil antelopes going back to the 

 late Oligocene or early Miocene periods, 

 some twenty-five million years ago, in- 

 clude several duikerlike forms from Eu- 

 rope, Asia, and North America. In most 

 cases, the evolution of antlers went along 

 with the diminution of large canines, al- 

 though some modem species (such as the 

 muntjac of Southeast Asia) retain large ca- 

 nines as well as homs. 



Stabbing homs represent the earliest 

 and simplest type of armament among a 

 great diversity of hom shapes and sizes. 

 But very soon after this type of antler ap- 

 peared in the late Oligocene, many large, 

 gregarious antelopes with antlerlike homs 

 were beginning to populate the newly 

 spreading grasslands of the Northern 

 Hemisphere. In open landscapes, the ani- 

 mals banded together to avoid predators, 

 for the larger the herd, the less likely that 

 any particular individual at its periphery 

 would be caught. Those in the center were 

 the safest of all. Zoologists call such ag- 

 gregations "selfish herds" because indi- 

 viduals do not cooperate but stay together 

 strictly in their own self-interest. 



In closely packed herds, a wounded an- 



Drawing by Valerius Geist 



66 Natural History 4/94 



