The rise and spread of tropical grasslands was a signal event in the Cenozoic, causing many ungulates to evolve adaptations to a diet of graminoid tissues, or graminivory. In parallel, a lineage of monkeys (Theropithecus) is distinguished among primates for its large size and commitment to graminivory, a trait expressed by species throughout the Plio-Pleistocene fossil record and T. gelada, the sole surviving species today. An open question concerns the mechanics of how fossil species of Theropithecus handled graminoid tissues. They might have exhibited preference, selecting tissues within a given tuft, or they might have practiced indiscriminate bulk-feeding in a manner similar to large grazing ungulates. To differentiate between these handling behaviors, we used time- and graminivore-calibrated carbon stable isotope values to show progressive reliance on high-throughput bulk-feeding graminivory. Variation in this behavior explains a significant amount of variation in body mass through time, and we describe these covarying traits, which peaked during the Pleistocene, as evolutionary traps. To support this characterization, we report evidence of temporal increases in strontium isotope variability among North African theropiths, a result that suggests greater lifetime travel and energetic costs in response to diminishing food resources, a probable factor in the extinction of T. oswaldi, the largest monkey that ever lived.

热带草原的兴起和扩散是新生代的一个信号事件，导致许多有蹄类动物进化出对类食性动物或食性食性的适应。同时，灵长类动物以其较大的规模和对食肉动物的承诺而在灵长类动物中被区分为猴子（Theropithecus），这是整个上新世化石化石记录中的物种和当今唯一幸存的物种T. gelada所表现的特征。一个悬而未决的问题涉及Theropithecus的化石物种的力学机制处理过的类皱纹组织。他们可能表现出偏爱，选择了给定簇中的组织，或者他们可能以类似于大型放牧有蹄类动物的方式进行了不加选择的批量喂养。为了区分这些处理行为，我们使用了经过时间和食虫动物校准的碳稳定同位素值，以显示对高通量批量食肉食动物的逐步依赖。这种行为的变化解释了随着时间的推移体重的显着变化，我们将这些变化的特征描述为更新陷阱，这些特征在更新世期间达到顶峰。为了支持这一特征，我们报告了北非食肉类动物中锶同位素变异性随时间增加的证据，这一结果表明，随着食物资源的减少，一生中的旅行和精力成本将增加，T. oswaldi，有史以来最大的猴子。