NOTHARCTUS

extinct genus of primitive primates (family Notharctidae) that were among the evolutionary ancestors of modern lemurs. The genus is well known from complete fossil remains found in Eocene deposits (those formed between 57.8 and 36.6 million years ago) in Europe and North America. Notharctus was small and resembled the modern lemurs on Madagascar. Its skull was about 5 cm (2 inches) long, with a prominent muzzle and a long lower jaw. Its canine teeth were still primitive, and four premolars were retained instead of three; but the upper incisors were relatively modern. The legs and tail were long and slim, and the first digit of the feet and hands was set off from the rest. Notharctus must have been an able and agile climber. During the Eocene it inhabited the dense subtropical forests that flourished over much of North America and Eurasia. At the close of the Eocene, conditions changed, and Notharctus and related forms disappeared from the Northern Hemisphere. Other, more modern lemurs continued on in tropical forests elsewhere and were particularly successful on Madagascar, where they remained relatively free from competition.