The Pliocene ungulate fauna from the hominid-bearing Laetolil succession (Southern Serengeti, Tanzania) is investigated with regard to dietary adaptation, niche segregation and change over time. The fossiliferous Upper Laetolil Beds (ULB) (3.63–3.85 Ma) are unconformably overlain by the Upper Ndolanya Beds (UNB) (2.66 Ma). Both stratigraphic units contain a rich mammalian fauna, with ungulates predominating. Analysis of dental mesowear is applied to 23 ungulate taxa from both units, including Equidae, Bovidae and Giraffidae, and the results are compared to extant species. The equids at Laetoli represent the only specialized grazers throughout the succession. All Upper Laetolil Alcelaphini and Hippotragini have mesowear signatures that indicate intermediate feeding strategies, different from their modern counterparts that are mostly specialized grazers. This indicates a dietary shift in these lineages, a finding that is also supported by isotope studies. Mesowear data of ungulates from the ULB also suggest that extant ungulates representing closely related lineages in the same genus or even tribe may not serve as actualistic model taxa in faunal reconstructions using taxonomic uniformitarianism. The three species of giraffids and the remaining bovid taxa were either browsers or intermediate feeders, but not grazers. The almost complete absence of grazing guilds, and the heavy reliance on browse by most fossil herbivores, do not support the inference that the Laetoli environment was dominated by grassland. Within the Laetoli succession it appears that fundamental feeding niches converged over time, with grazers increasingly engaged in feeding on less abrasive components and intermediate-feeders closing the dietary gap by exploiting more abrasive feeding niches. Niche partitioning in the Laetoli ungulates appears to reflect environmental change and evolutionary trajectories in the major lineages. This distribution of feeding niches may serve as an overall indicator of niche diversity. Within the succession it appears that the diversity of feeding niches generally decreased. A decrease in feeding niches would suggest that the diverse habitat structure, which was typical of the ULB environment, no longer existed after the faunal and environmental transition that occurred after deposition of the ULB. After a hiatus of 1.0 million years, the UNB environment was more or less free of forest and woodland patches and can be characterized as more or less open grassland.