Small Mon­key Gave Up Jump­ing

Science Illustrated - - HUMANS -

The first pri­mates crawled about 65 mil­lion years ago, in the time of Tyran­nosaurus rex, ac­cord­ing to ge­netic stud­ies of mod­ern an­i­mals. But sci­en­tists have still not dis­cov­ered the re­mains of the early pri­mates, as the old­est known fos­sils only date back from the time af­ter the dis­ap­pear­ance of the di­nosaurs.

No mat­ter when the ancestor of the pri­mates lived, sci­en­tists know that the fam­ily tree soon branched out in two. One branch led to strep­sir­rhini, in­clud­ing lemurs and lo­ries, whereas the other branch, in which we be­long, led to true mon­keys. So far, sci­en­tists have not found many fos­sils which can help them un­der­stand this, but one sin­gle an­i­mal sheds light on the mat­ter. Eosimias, which only weighted 100 g, was so small that it could sit in a hu­man hand, but it still had a lot in com­mon with us.

Eosimias’ heel shows signs of a tran­si­tion from feet de­signed for long jumps (lemur be­hav­iour) to feet which were pri­mar­ily used to walk on branches. This very char­ac­ter­is­tic shows that Eosimias was pre­sum­ably an early type of mon­key. Con­se­quently, the small an­i­mal prob­a­bly had a rel­a­tively large brain and ex­cel­lent colour vi­sion just like its de­scen­dants. Colour vi­sion is rare among mam­mals, and most likely used the new char­ac­ter­is­tic to find colour­ful fruit among the leaves of the trees.

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