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Human ancestor ate bark, study finds

June 27, 2012
Courtesy of the University of Colorado at Boulder
and World Science staff

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.

The hominid Aus­tra­lo­pith­e­cus sed­iba. (Cred­it: Paul Sand­berg, U. Co­lo­r­a­do)


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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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” because of 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 is 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 at the time just prior to death—also confirmed at least one of the hominids was eating harder foods, said Sandberg.