The oldest known primate skeleton and early haplorhine evolution

Reconstructing the earliest phases of primate evolution has been impeded by gaps in the fossil record, so that disagreements persist regarding the palaeobiology and phylogenetic relationships of the earliest primates. Here we report the discovery of a nearly complete and partly articulated skeleton of a primitive haplorhine primate from the early Eocene of China, about 55 million years ago, the oldest fossil primate of this quality ever recovered. Coupled with detailed morphological examination using propagation phase contrast X-ray synchrotron microtomography, our phylogenetic analysis based on total available evidence indicates that this fossil is the most basal known member of the tarsiiform clade. In addition to providing further support for an early dichotomy between the strepsirrhine and haplorhine clades, this new primate further constrains the age of divergence between tarsiiforms and anthropoids. It also strengthens the hypothesis that the earliest primates were probably diurnal, arboreal and primarily insectivorous mammals the size of modern pygmy mouse lemurs. Understanding the earliest phases of primate evolution is obscured by gaps in the fossil record, but some light is shed by the discovery of a nearly complete and substantially articulated skeleton of a tiny primate from the early Eocene; the new primate lies near the pivotal evolutionary dichotomy separating the tarsier and anthropoid lineages and it possesses features that are characteristic of subsequent members of both lineages. A well preserved early primate Our knowledge of the earliest phases of primate evolution is limited by the gaps in the fossil record. Some light is shed by the discovery of a nearly complete and substantially articulated skeleton of a tiny and very ancient primate from the early Eocene of China, dating to 55 million years ago. The newly discovered primate appears to be the earliest known relative of the tarsiers, suggesting a very early divergence of the anthropoid lineage from the other primates. The animal was about the size of the modern pygmy mouse lemur, and skeletal features suggest that it was an agile insectivore with a diurnal habit.