A team of researchers from the University of Michigan and the University of Oxford has uncovered new evidence about the evolution and behavior of early primates in Egypt, 30 million years ago. The scientists analyzed the fossil teeth of two extinct monkey species, Aegyptopithecus and Parapithecus, and found that they had different dietary preferences and ecological niches. The study, published in the journal Proceedings of the National Academy of Sciences, sheds light on how ancient monkeys adapted to a changing climate and environment in the Oligocene epoch.
The fossil teeth were collected from the Fayum Depression, a rich paleontological site in the Western Desert of Egypt. The Fayum is known for its diverse and well-preserved fossils of mammals, birds, reptiles, and plants, dating back to the Eocene and Oligocene epochs, 56 to 23 million years ago. The Fayum primate fauna is especially important, as it represents the earliest known catarrhine primates, the group that includes Old World monkeys, apes, and humans.
Aegyptopithecus and Parapithecus: two distinct monkey lineages
Among the Fayum primates, Aegyptopithecus and Parapithecus belong to two distinct lineages that diverged from a common ancestor around 40 million years ago. Aegyptopithecus is considered to be the most primitive known hominoid, the group that includes gibbons, orangutans, gorillas, chimpanzees, and humans. Parapithecus, on the other hand, is a member of the parapithecid family, a group of monkeys that is closely related to the platyrrhines, the New World monkeys of South and Central America.
The researchers examined the shape, size, and wear patterns of the fossil teeth of Aegyptopithecus and Parapithecus, using a combination of microscopic and 3D imaging techniques. They compared the teeth with those of living primates and other mammals, and used statistical methods to infer the diet and ecology of the extinct species.
Different diets reflect different adaptations
The results showed that Aegyptopithecus and Parapithecus had different diets, despite living in the same region and time period. Aegyptopithecus had large, bunodont molars, with rounded cusps and thick enamel, similar to those of living apes. These teeth are well-suited for crushing hard and tough foods, such as seeds, nuts, and insects. Parapithecus, on the other hand, had smaller, bilophodont molars, with two parallel ridges and thinner enamel, similar to those of living Old World monkeys. These teeth are well-suited for slicing soft and juicy foods, such as fruits and leaves.
The researchers also found that Aegyptopithecus and Parapithecus had different degrees of dental wear, indicating different rates of tooth eruption and replacement. Aegyptopithecus had more worn teeth, suggesting that it had a slower dental development and a longer lifespan than Parapithecus. Parapithecus had less worn teeth, suggesting that it had a faster dental development and a shorter lifespan than Aegyptopithecus.
Implications for primate evolution and climate change
The study reveals that Aegyptopithecus and Parapithecus had different adaptations to cope with the changing climate and environment in the Oligocene epoch. The Oligocene was a time of global cooling and drying, which resulted in the expansion of grasslands and the reduction of tropical forests. The researchers suggest that Aegyptopithecus was more flexible and opportunistic in its diet and ecology, and could exploit a variety of food resources in different habitats. Parapithecus, on the other hand, was more specialized and selective in its diet and ecology, and relied on the availability of fruits and leaves in the remaining forest patches.
The study also has implications for understanding the evolutionary history and biogeography of early primates. The researchers propose that the divergence of Aegyptopithecus and Parapithecus reflects the separation of the catarrhine and platyrrhine lineages, which occurred around 40 million years ago. The catarrhine lineage remained in Africa and gave rise to the Old World monkeys and apes, while the platyrrhine lineage migrated to South America and gave rise to the New World monkeys. The researchers suggest that the parapithecid family, which includes Parapithecus, represents the closest relatives of the platyrrhines, and that they share a common ancestor that lived in humid forests along the western coast of Africa.
The study demonstrates the importance of fossil teeth for reconstructing the diet and ecology of extinct primates, and for revealing the evolutionary and environmental factors that shaped their diversity and distribution. The study also provides new insights into the origins and adaptations of early monkeys, and their responses to climate change in the past.
