Morethan 3 millionyears ago, when “Lucy” was roaming the savannah of present-day Ethiopia, she may haveencounteredother two-leggedapes not unlike her own species, Australopithecusafarensis—yet stilljust a wee bit strange.
Represented by jawbonesfromthreeindividuals, a newlydescribedspeciesnamedAustralopithecusdeyrimedaadds to
the scatter of evidencethat not one, but a range of homininspeciespopulated the EastAfricanlandscapebefore 3 millionyears
ago. Thiscouldimplytheywereable to carve out separateniches in a stableenvironmentbased on differences in diet, foragingstrategies and otherbehaviors.
“We don't knowenough yet to say anythingabout the nature of interaction or ecologicaldifferencesbetween A. afarensis
and A. deyiremeda,” saysStephanieMelillo of the Max PlanckInstitute for EvolutionaryAnthropology. “We have to firstknow
how to tell the two speciesapartfromtheirfossilremains, and that is whatthispaper was all about.”
ReportedWednesday in Nature, the new specimens—a partialupper jaw, two lowerjaws, and someotherfragments—werefound at Burtele, in the AfarTriangle of Ethiopia, just a day’s walkfromHadar, whereLucy was found in
1974. Sedimentssurrounding the bonesweredated to 3.3 and 3.5 millionyears ago, a timewhen A. afarensis is wellknown to
haveinhabited the region. While the new jawssharesomecharacteristicswithLucy’s species, theydiffer in otherrespects.
Some of the teethhavedifferentrootstructures, and in general are smallerthan A. afarensisteeth, a traitthatcouldindicate a
shift in diet.
“Smallerteeth are oftenassociatedwith a moremeatydiet,” saysFredSpoor of UniversityCollegeLondon and the Max
PlanckInstitute for EvolutionaryAnthropology. “And the chewingmuscleshavemigratedforward, whichsuggests a
redistribution of chewingforces of somesort.”
The speciesname, A. deyrimeda, derivesfrom the localwords for “close” (deyi) and “relative” (remeda)—signaling the
speciescloserelationshipwithotherhominins. But the similaritiesonly go so far.
“We are convincedthat it is differentfrom A. afarensis. All of the evidence—published and unpublished—that we havefrom the localities at Burtelesupport our conclusion,” saysstudyauthorYohannesHaile-Selassie of the ClevelandMuseum of
NaturalHistory. He notesthatfolding the new specimensinto A. afarensiswouldintroduce an extremelyunusualamount of
physicalvariationinto the existingspecies.
Still, “the distinctions are very, verysubtle,” sayspaleoanthropologistBillKimbel of the Institute of HumanOrigins. “I
think the authorshavedone a verynice job in analyzing the material, but I think it’s a judgmentcall as to whether you think the
differencesamount to a species-leveldifference.”
A. afarensisremains by far the mostconspicuoushominin in the fossilrecord of EastAfrica 3 to 4 millionyears ago,
during a periodknown as the MiddlePliocene. But in the last two decades, scientistshavenamedseveralothers, includingAustralopithecusbahrelghazalifromChad, and KenyanthropusplatyopsfromKenya. A. deyrimedafurtherswells the crowd.
“There is now incontrovertibleevidence to showthatmultiplehomininsexistedcontemporaneously in easternAfricaduring the MiddlePliocene,” the authorswrite.
Of specialinterest are someenigmaticfootbones of a homininrecovered in 2009 veryclose to where A. deyiremeda was
unearthed. The bonessuggest a creaturewith a flexiblefoot and big toe capable of graspingobjects, similar to a moreprimitivehominincalledArdipithecusramidus, dated to 4.4 millionyears ago.
But perplexingly, the footbones at Burteledateback to just 3.4 millionyears ago: the sametimeperiod as A. deyiremeda.
It’s a combination of proximity in bothspace and timethatcannot be ignored, Kimbelsays.
“Figuring out whether or not thatveryprimitivefoot is the samecritter as the clearaustralopithecineteeth and jawsthat
are beingdescribed now is of utmostimportance,” Kimbelsays. “It wouldmeanthat you couldhaveaustralopithecus-likeheadswithmorediverseoptions for locomotion – which is not a picture we havepainted so far.”
【題組】50. How manyhomininsreside in the easternAfricanbefore 3 millionyears ago?
(A) one (B) two (C) morethan two
(D) none (E) The answer is stillcontrovertible.