Mammals in Sulawesi: where did they come from and when, and what happened to them when they got there?

It is evident that part, at least, of Sulawesi is of Sundaland origin. If there was a dry-land connection between Sulawesi and Sundaland in the Pliocene, this would be compatible with the observation that most of Sulawesi’s mammals are endemic at the level of genera, subgenera or well-differentiated species-groups. In some cases their closest relations seem to be with mammals from the Tatrot stage of the Siwaliks, presumably via the poorly-known “Siva-Malayan” fauna of Java. Within Sulawesi both altitudinal and geographic speciation are well-marked. The groups in which geographic variation is most easily appreciated are monkeys and squirrels. Combining the data from these groups indicates that species of the southern and southeastern peninsulas separated earliest; those of the central part and the northern peninsula form a single clade. What little is known of the fossil mammals of Sulawesi comes from the Pliocene Walanae Formation on the southern peninsula. Surprisingly, this is not known to contain anoa, babirusa or any of the other present-day endemics, but pygmy elephantids and the giant pig Celebochoerus. Until Neogene palaeontology gets started on other parts of Sulawesi we have no explanation for this apparent anomaly, but it has been proposed more than once that Sulawesi was a cluster of separate islands until quite late in geologic time.