National Geographic : 2017 Apr
0mi 100 0km 100 Average length (male) 2 feet Gelada Olive baboon GreatRiftValley Ras Dejen 14,928 ft 4,550 m ETHIOPIAN HIGHLANDS Addis Ababa Debre Birhan Mekele Gonder Bahir Dar Dessie Mehal Meda Asela ETHIOPIA SUDANETHIOPIA YEMEN DJIBOUTI ERITREAETHIOPIA Menz-Guassa Community Conservation Area Simien Mts. National Park Lake Tana Awash Red Sea BlueNile AFRICA AREA ENLARGED ETHIOPIA Gelada range MALE GELADA MALE OLIVE BABOON MANUEL CANALES AND LAUREN C. TIERNEY, NGM STAFF; SHIZUKA AOKI; TONY SCHICK SOURCES: RYAN J. BURKE, UNIVERSITY OF OXFORD; VIVEK VENKATARAMAN, HARVARD UNIVERSITY; JEFFREY KERBY, DARTMOUTH COLLEGE; PETER FASHING AND NGA NGUYEN, CSU FULLERTON; BIREN PATEL, UNIVERSITY OF SOUTHERN CALIFORNIA Survival of the Grass-Eaters The geladas of the Ethiopian Highlands are often mistaken for baboons but are actually the last members of their own genus, Theropithecus. The unique morphology, diet, and behavior of the world’s only grass-eating monkeys are helping scientists hunt for clues about primate evolution. Highland refuge Living at high, harsh elevations shielded geladas from competitors as a shifting climate drove other Pleistocene grass-eaters to extinction. Red chests Geladas’ red chest patches are unique among primates and are highly visible, even while they sit to forage— which is most of the time. Among male geladas, dominant individuals have the reddest coloring. Grass-grinding teeth Geladas’ canines are for fighting and display, with smaller incisors and larger, serrated molars for grinding grass. Baboons are omnivores. Gripping hands Geladas’ longer, stronger thumbs and relatively shorter index fingers give them a pincerlike grip for pulling grass. CLOSEST LIVING RELATIVES Geladas (below, left) are similar to baboons, but with key evolutionary differences. A male’s thick cape provides warmth and may attract females.