Miocene reef-coral diversity of Indonesia: unlocking the murky origins of the Coral Triangle

Abstract

Reefs in the Coral Triangle host the richest marine diversity today. While the biodiversity gradients associated with the Coral Triangle are progressively better documented, the mechanisms responsible for the origins and maintenance of this pattern still remain obscure. Until recently, palaeontological and molecular evidence suggest that the Miocene (5-23 Ma) was an important period for diversification of corals and associated biota in this region. However, the fossil record was markedly undersampled. As part of the Throughflow Project (TF), the main objective of this research was to obtain insights into the early history of today’s Coral Triangle diversity and understand its major ecological drivers. Corals play an essential role in the diversity of this region, not only due to the richness of the group itself, but also because they are the main reef builders and coral reefs are the main ecosystem in which diversity thrives. In addition, corals possess carbonate skeletons with a high potential of fossilization. These characteristics make corals an interesting model group to carry on taxonomic, phylogenetic and palaeoecological studies. The new TF collections include tens of thousands of specimens from the rich and well-preserved Miocene fossil record of small patch reefs in the Kutai Basin (East Kalimantan, Indonesia). These reefs developed in turbid habitats. A high diversity of corals was uncovered, with a total of 234 identified morphospecies from 79 genera, including 12 globally extinct genera. Our findings have revealed that some lineages that were previously known only from the Plio-Pleistocene were already present during the Miocene in the Coral Triangle. These discoveries have a profound impact on our understanding of the origins of today’s diversity in the Coral Triangle.