A new Middle Miocene tarsier from Thailand and the reconstruction of its orbital morphology using a geometric–morphometric method

<jats:p> <jats:italic>Tarsius</jats:italic> is an extant genus of primates endemic to the islands of Southeast Asia that is characterized by enormously enlarged orbits reflecting its nocturnal activity pattern. Tarsiers play a pivotal role in reconstructing primate phylogeny, because they appear to comprise, along with Anthropoidea, one of only two extant haplorhine clades. Their fossils are extremely rare. Here, we describe a new species of <jats:italic>Tarsius</jats:italic> from the Middle Miocene of Thailand. We reconstructed aspects of its orbital morphology using a geometric–morphometric method. The result shows that the new species of <jats:italic>Tarsius</jats:italic> had a very large orbit (falling within the range of variation of modern <jats:italic>Tarsius</jats:italic> ) with a high degree of frontation and a low degree of convergence. Its relatively divergent lower premolar roots suggest a longer mesial tooth row and therefore a longer muzzle than in extant species. The new species documents a previous unknown Miocene group of <jats:italic>Tarsius</jats:italic> , indicating greater taxonomic diversity and morphological complexity during tarsier evolution. The current restriction of tarsiers to offshore islands in Southeast Asia appears to be a relatively recent phenomenon. </jats:p>