Small, odd and old: The mysterious Tarsius pumilus is the most basal Sulawesi tarsier

In this study we present the first genetic evidence of the phylogenetic
position of Tarsius pumilus, the mountain tarsier of Sulawesi, Indonesia.
This mysterious primate is the only Eastern tarsier species that occurs
exclusively in cloud forests above 1800 m asl. It exhibits striking
morphological peculiarities – most prominently its extremely reduced body
size, which led to the common name of “pygmy tarsier”. However, our
results indicate that T. pumilus is not an aberrant form of a lowland
tarsier, but in fact the most basal of all Sulawesi tarsiers. Applying a
Bayesian multi-locus coalescent approach we dated the divergence between
the T. pumilus lineage and the ancestor of all other extant tarsiers to
9.88 MYA. This is as deep as the split between the two other tarsier
genera Carlito (Philippine tarsiers) and Cephalopachus (Western tarsiers),
and predates further tarsier diversification on Sulawesi by around 7
million years. The date coincides with the deepening of marine environment
between eastern and western Sulawesi, which likely led to allopatric
speciation between T. pumilus or its predecessor in the west and the
ancestor of all other Sulawesi tarsiers in the east. As the split preceded
the emergence of permanent mountains in western Sulawesi, it is unlikely
that the shift to montane habitat has driven the formation of the T.
pumilus lineage.