Robust australopithecines (Paranthropus) had larger cheek teeth than gracile australopiths, possibly because robust australopithecines had more tough, fibrous plant material in their diets, whereas gracile australopiths ate more hard and brittle foods. However, such divergence in chewing adaptations may instead have been a response to fallback food availability. In leaner times, robust and gracile australopithecines may have turned to different low-quality foods (fibrous plants for the former, and hard food for the latter), but in more bountiful times, they had more variable and overlapping diets. In a 1979 preliminary microwear study of Australopithecus fossil teeth, anthropologist Alan Walker theorized that robust australopiths ate predominantly fruit (frugivory).
rObust australopiThecInEs (paRanthropUs) haD largEr cheEK TEeTh THaN GraciLE aUstrALopiThs, possibly beCaUse robuST AuStRAlopithECInes had More tOUgh, fIbroUs plant mateRIaL iN thEir DiEts, wherEas GRaciLe australopIthS aTE More HaRd And BritTle fOOds. howEVER, SucH DivERgeNCe in CHewiNg aDaPtatIONs MAY iNstEAd HAve beEn a rESpOnse to FAllBaCk fOOD AVaIlabilIty. in lEanER timEs, roBust AnD GrAciLe australopiTHeciNes may hAve tURned To DIffERENt lOw-quaLity FooDs (fiBRous PlaNTs fOr THe FoRmER, aNd Hard fOoD FOR ThE LaTtEr), bUT IN mOre bOunTIfUl tIMes, they haD moRE VariaBle And overLapPIng diets. in a 1979 pReliMinary micRoweaR sTuDy Of ausTRAlopiThEcuS Fossil TEeth, anTHropologiSt alaN WalKeR tHEORiZed tHAt robUst aUstraLopItHs Ate prEdOmInantlY fruIT (fRuGivOrY).