Final answer:
The large molars and thick tooth enamel of australopithecines are adaptations for eating tough plant materials.
Step-by-step explanation:
The large molars and thick tooth enamel of australopithecines are likely adaptations for eating tough plant materials. The sagittal crest in the robust australopithecines allowed for the accommodation of large jaw muscles used for chewing such tough plant materials. Fossil evidence suggests that australopithecines had a diet rich in gritty foods such as nuts, seeds, and fruits with tough peels, which would have required strong teeth and jaws.