Theropithecus oswaldi, during the early Pliocene. Most plant groups are placed into one of three categories, C3, C4 and CAM (Crassulacean acid metabolism). The main difference between the plants concerns the photosynthesis process: C4 plants process atmospheric carbon into a compound with four carbon atoms, whereas C3 convert it into a compound with just one. CAM plants on the other hand, are capable of using either pathway for photosynthesis. The crucial consequence of this difference is that C4 plants are much more suited to growing in a hot, dry climate – they photosynthesize at a faster rate and in a way which involves significantly less water loss. Examples of C4 plants include maize, millet, papyrus and sugarcane, while C3 plants include rice, wheat, spinach, potatoes and yams. By expanding their diet to include C4 plants, hominins may have been able to increase the variety of environments in which they could survive, or increase their chances of survival in more changeable environments. 152 fossil teeth from the Woranso-Mille site in Ethiopia were subjected to analysis as part of the study. The distinct carbon isotope signatures of C3 and C4 plants mean that the composition of an animal’s diet can easily be determined through their tooth enamel. This method allowed the scientists involved to fill in gaps about the chronology of the evolution of early hominin diets. “Fossil teeth from the Woranso-Mille paleontological study area are well-suited to fill the temporal gap in the isotopic record of hominin diet because they are part of a record of Pliocene mammalian fossils that spans 3.76–3.2 Ma”. The Pliocene is one of the most important periods in the evolution of humans, when early hominins left the trees and increasingly walked on two legs, and their diets diversified massively to include a much wider range of food sources than their ancestors. Consuming C4 foods was a crucial part of this transition. As the study explains, “The incorporation of C4 resources into hominin diet signifies increased dietary breadth within hominins and divergence from the dietary patterns of other great apes.” The analysis showed that both hominins and Theropithecus included substantial amounts of C4 foods in their diet as far back as 3.76 million years ago. In comparison, other primates and mammals showed evidence of widespread C4 consumption much earlier, as far back as the late Miocene period (11.6 to 5.3 million years ago). Although occurring at a similar time, the diversification into a C4 diet had different consequences for Theropithecus and hominins. For Theropithecus, it marked the beginnings of a dietary specialisation which culminated in them assuming the role of a grazer among the mammal species of Africa. For hominins on the other hand, the transition came in the wake of significant dentognathic changes which were part of a general broadening of their diets. As the study concludes, these changes played a significant role in the development and spread of hominins, and were subsequently vital to human evolution. “The unequivocal incorporation of C4 resources by hominins and cercopithecids as early as 3.76 Ma demonstrates that primates were expanding the types of food resources and potentially the environments that they were able to exploit.” For more information: www.pnas.org Image courtesy of Wikimedia Commons user: Thamizhpparithi Maari]]>
