【化石】北米のサルをめぐる謎が解き明かされる

Seven fossilised teeth discovered during the expansion of the Panama Canal suggest monkeys were present in Central America much earlier than previously thought, reports a paper published in Nature. The 21-million-year-old fossils are the earliest known evidence for the movement of mammals between North and South America.

New World monkeys (playtrrhines) are part of the modern tropical ecosystems of both North and South America. However, these continents were separated by an ocean until the Isthmus of Panama linked them about 3.5 million years ago. Genetic estimates suggest New World monkeys did not arrive in Central America, the southern-most part of the North American landmass, until this time, but the complete absence of fossils has limited our understanding of their history.

Jonathan Bloch and colleagues discovered the teeth in the Las Cascadas Formation in the Panama Canal Basin, Panama, and suggest that they represent the first fossil monkey discovered on the North American landmass. Their analyses indicate that the New World monkeys diversified into their current five extant families (Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae) about 22-25 million years ago. The discovery of the fossil, the authors conclude, provides evidence that the New World monkeys were distributed around the Caribbean Sea by that time. They suggest that the monkeys’ further northward movement was probably limited more by the difference in evolutionary histories and species of North versus South American forests than by differences in climate or the existence of major geographic barriers.