The paragraphs below are taken from Evolution and Geological Significance of Larger Benthic Foraminifera, BouDagher-Fadel, M. K., Elsevier, 2012 (2nd edition).

The foraminifera are free-living protozoa that grow an elaborate, solid calcite skeleton. The complexity of their shell structure is the basis of their geological usefulness. The systematic study of fossilized, so-called “larger benthic foraminifera” (LBF), found in abundance among the corals, molluscs and algae in tropical and subtropical reef-derived limestones, began in the in the 1920s in the Dutch East Indies with the studies pioneered by micropalaeonotologists such as Tan Sin Hok. Tan Sin Hok’s work made a major and original contribution to the taxonomy and palaeoecology of the LBF, putting their usefulness on a firmer footing than it had ever enjoyed before. In his evolutionary taxonomic studies, Tan Sin Hok explored the morphological/phylogenetic evolution of the Indo-Pacific larger benthic foraminifera, thus establishing the morphogenetic method, by which successive events observed in the fossil record, constituting an evolutionary “bioseries”, could be confirmed as occurring in an orderly way in the same evolving lineage in different regions. He also was a main contributor to the so-called “Indo-Pacific Letter Classification” of Cainozoic biostratigraphy, spreading its use to India, Northern Australia, and the islands of the western Pacific. This enabled effective correlations to be made between different sedimentary basins, and has played a major role in the successful exploration of oil and gas fields in the region.

Tan Sin Hok was the first to emphasize the importance of the peri-embryonic chambers in the evolution of LBFs (giving rise to the evolutionary theory of nepionic acceleration, see BouDagher-Fadel 2008). Several classic examples of his evolutionary studies of the Indo-Pacific larger benthic foraminifera are still relevant today. His work explored the systematic and biostratigraphic usefulness of many important evolutionary lineages of LBF. Tan Sin Hok was the first to explore the anatomical and morphometrical analysis of the important family Miogypsinidae. His studies also underpin our understanding of the phylogenetic history of the genus Cycloclypeus and related species in the family Nummulitidae. The basic data on these two families was gathered on geological fieldworks during his time in the East Indies (Indonesia and its surroundings) and the wider Indo-Pacific region. Subsequently, many micropaleontologists built on his remarkable insights in the study of the LBF, and his theory of nepionic acceleration with time, proved to be of general paleontological interest as well as of stratigraphical importance.

There is no doubt that Tan Sin Hok was one of the founding fathers of mircopalaeonotology, and his legacy lasts to this day, as a testimony to an insightful and brilliant palaeonotologist and geologist.