Friday, July 6, 2012

Human ancestor ate bark, study finds

Next time you’re grum­bling about a stale cook­ie or a steak that tastes “like card­board,” count your­self lucky that you’re not Aus­tra­lo­pith­e­cus sed­iba, the hu­man an­ces­tor who ate bark. At least, that’s what sci­en­tists say about A. sed­iba, a short, gangly South Af­ri­can spe­cies from two mil­lion years ago. Their study indica­tes the crea­ture tar­geted trees, bushes and fruits for its di­et, chomp­ing on harder foods than oth­er oth­er known early ho­minids, or hu­man an­ces­tors. Vir­tu­ally all oth­ers that have been tested from Africa—in­clud­ing Paran­thro­pus boi­sei, dubbed “Nutcracker Man” thanks to its mas­sive jaws and teeth—fo­cused more on grasses and sedges, ac­cord­ing to an­thro­po­l­ogy doc­tor­al stu­dent Paul Sand­berg of the Uni­vers­ity of Col­o­rad­o Boul­der, a co-author of the new stu­dy. The find­ings were pub­lished in the June 27 on­line edi­tion of the re­search jour­nal Na­ture. Sci­en­tists an­a­lyzed the A. sed­iba di­et by zap­ping fos­sil­ized teeth with a la­ser, said Sand­berg. The la­ser breaks off tell­tale car­bon from the enam­el of teeth, so re­search­ers can pin­point which types of plants the car­bon comes from. The re­sults show which of two groups of plants were con­sumed: so-called “C3” plants like trees, shrubs and bushes pre­ferred by A. sed­iba, and “C4” plants like grasses and sedges con­sumed by many oth­er early ho­minids. The teeth from both A. sed­iba in­di­vid­u­als an­a­lyzed had lev­els of C3 out­side the range of all 81 pre­vi­ously tested ho­minids, the re­search­ers re­ported. “The lack of any C4 ev­i­dence, and the ev­i­dence for the con­sump­tion of hard ob­jects, are what make the in­ferred di­et of these in­di­vid­u­als com­pelling,” said Sand­berg. “It is an im­por­tant find­ing be­cause di­et is one of the fun­da­men­tal as­pects of an an­i­mal, one that drives its be­hav­ior and ec­o­log­i­cal niche. As en­vi­ron­ments change over time be­cause of shift­ing clima­tes, an­i­mals are gen­er­ally forced to ei­ther move or to adapt to their new sur­round­ings,” said Sand­berg.
The re­search­ers con­clud­ed that bark and oth­er “fracture-resistant” foods were at least a sea­son­al part of the A. sed­iba di­et. Some mod­ern apes and their rel­a­tives eat bark and woody tis­sues, which con­tain pro­tein and sug­ars. The di­et of A. sed­iba may have been si­m­i­lar to that of to­day’s Af­ri­can sa­van­na chim­panzees, Sand­berg said. A un­ique as­pect of the proj­ect was the anal­y­sis of mi­cro­scop­ic, fos­sil­ized par­t­i­cles of plant tis­sue known as phy­toliths trapped in an­cient tooth tarter, a hard­ened form of den­tal plaque, said study co-author Aman­da Hen­ry of the Max Planck In­sti­tute for Ev­o­lu­tion­ary An­thro­po­l­ogy in Leip­zig, Germany. “The fact that these phy­toliths are pre­served in the teeth of two-mil­lion-year-old ho­minids is re­mark­a­ble and speaks to the amaz­ing pre­serva­t­ion at the site,” said Sand­berg. “The phy­tolith da­ta sug­gest the A. sed­iba in­di­vid­u­als were avoid­ing the grasses grow­ing in open grass­lands that were abun­dant in the re­gion at the time.” A third, in­de­pend­ent line of stu­dy—analyzing mi­cro­scop­ic pits and scratch­es on A. sed­iba teeth, which re­veal what they were eat­ing short­ly before death—also con­firmed at least one of the ho­minids was eat­ing hard foods, said Sand­berg.

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