horns grow directly over the eye sockets. 

 In merycodonts, however, the horns have 

 multiple branches and often have encir- 

 cling rings of bone, or burrs, on the shaft 

 of the horn. In contrast, antilocaprine 

 horns are burrless and branch just once 

 from a common shaft. 



More remarkable is the asymmetry of 

 Ramoceros horns. Each side of the horns 

 has three branches, but the branches on the 

 left are twice as large as those on the right. 

 When horns like these were first described 

 scientifically, the unevenness was re- 

 garded as the result of injury. But many 

 specimens have now been found and stud- 

 ied, and all show such unequal horns. (The 

 smaller, more horizontal branch may be 

 on either the right or left, the incidence 



being about fifty-fifty.) Such striking 

 asymmetry is rare in mammals, although 

 perfect bilateral symmetry is also rare. 



In large museum collections of some 

 species of merycodonts, somewhat less 

 than 50 percent of the adults are hornless 

 and most likely represent females. We do 

 not yet have a large enough sample of 

 Ramoceros species to measure the inci- 

 dence of homlessness, but we assume that 

 these merycodonts, too, will eventually 

 show such sexual dimorphism. Both sexes 

 of living pronghoms have horns, although 

 the females' are smaller Reproduction is 

 strongly seasonal in pronghorns, with 

 males vigorously competing for females 

 in the fall. With even more striking differ- 

 ences between the sexes, merycodonts, in- 



cluding Ramoceros, probably also came 

 together in herds and reproduced season- 

 ally. The males' di.splay of horns may have 

 been important in attracting and compet- 

 ing for females. 



In the Museum's mount, ntxHntr Amph- 

 icyon nor Ramoceros wins out; the preda- 

 tor is always pursuing, the prey ever evad- 

 ing the attack. We have no way of 

 knowing which creature won more often 

 in actual chases those millions of years 

 ago. In the evolutionary stakes, however, 

 Ramoceros was the victor. The last Amph- 

 icyon died out some fourteen million years 

 ago. The family to which Ramoceros be- 

 longed flourished for twenty million years 

 and gave rise to modern pronghorns, 

 which carry on the lineage today. 



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