A fos­silised face stares up through the mi­cro­scope lens. The bizarre fos­sil pro­vides sci­en­tists with ex­tremely de­tailed in­sight into the be­gin­ning of 540 mil­lion years of hu­man evo­lu­tion.

Science Illustrated - - HUMANS -

540 mil­lion years ago

Atiny mon­ster is wrig­gling be­tween the sand grains. With a large mouth sur­rounded by wrin­kled skin folds, it con­sumes every­thing that it can get hold of, forc­ing the re­mains out through blunt spikes on the side of its body.

The odd crea­ture’s fos­silised re­mains, which only mea­sure 1 mm, have just been dis­cov­ered by a team of sci­en­tists. The an­i­mal has been named Sac­corhy­tus (wrin­kled sack), and the dis­cov­ery sheds much needed light on the first branches of our fam­ily tree.

Ge­netic stud­ies have long shown that hu­mans and all other ver­te­brates are re­lated to echin­o­derms such as starfish, sea urchins, and sea cu­cum­bers, but the fos­sil re­mains of the com­mon ancestor of hu­mans and sea cu­cum­bers has so far es­caped palaeon­tol­o­gists' at­ten­tion. Sac­corhy­tus fits into this very im­por­tant spot on the fam­ily tree, and the tiny crea­ture helps sci­en­tists un­der­stand how the founda-tions of the hu­man body were laid.

Like us, Sac­corhy­tus was char­ac­terised by mid­line sym­me­try. Its thin, flex­i­ble skin prob­a­bly cov­ered mus­cles and a prim­i­tive ner­vous sys­tem, which al­lowed the an­i­mal to wrig­gle for­ward on the bed of a shal­low sea in what is now China. More­over, sci­en­tists be­lieve that the an­i­mal’s spikes could be an ini­tial stage of hu­man branchial arches, which play an im­por­tant role in em­bry­onic devel­op­ment.

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