Seed Dispersal Coevolution with the Extinct Proboscidean Stegodon trigonocephalus Restricts Current Platymitra macrocarpa Distribution in Indonesia

The coevolution between angiosperms and megafaunal frugivores remains poorly understood despite its importance in shaping modern plant community dynamics and dispersal systems. Platymitra macrocarpa (Annonaceae) is a Southeast Asian tree species predicted to have coevolved with extinct proboscideans. This study investigates whether the extinct Javan proboscidean Stegodon trigonocephalus served as its primary seed disperser, influencing the plant’s current restricted distribution. Data were collected from literature reviews and secondary sources, including Herbarium Bogoriense for P. macrocarpa distribution and fruit-seed dimensions, and the Sangiran Museum for Stegodon fossil localities. Statistical correlation between P. macrocarpa distribution and S. trigonocephalus fossil records across Java was analyzed using SPSS, followed by spatial mapping with ArcGIS. The logistic regression analysis revealed a strong positive correlation (Nagelkerke R² = 0.854, p < 0.05) between S. trigonocephalus fossil distribution and P. macrocarpa occurrence, with a model accuracy of 94.4%. These results support a historical ecological association between the two species. Phylogenetic evidence indicates P. macrocarpa descended from Polyalthioxylon platymitroides, a Miocene taxon that migrated from India to Southeast Asia, reinforcing its long evolutionary history with megafaunal browsers. The extinction of Stegodon likely caused dispersal limitation and population fragmentation in P. macrocarpa, a phenomenon consistent with megafaunal dispersal evolutionary anachronism. This study concludes that P. macrocarpa distribution in Indonesia is a relict of its coevolution with S. trigonocephalus, and emphasizes the ecological legacy of extinct megafauna on tropical plant biogeography.