Fossil Insights Into Habitat Conservatism and Biogeographic Disjunction in Tetrameristaceae

ABSTRACT Disjunct distributions provide key insights into the processes shaping tropical biodiversity, yet their underlying mechanisms remain incompletely understood. The tropical family Tetrameristaceae exhibits a striking amphi‐Pacific disjunction, with its three genera isolated across the Neotropics and Southeast Asia: Pelliciera Planch. & Triana in Neotropical mangroves, Pentamerista Maguire in lowland savannas of northern South America, and Tetramerista Miq. in peat swamp forests of western Malesia. However, the processes governing this distribution remain unclear, largely due to a sparse fossil record restricted to Pelliciera . Here, we report the first fossil evidence of Tetramerista , Tetrameristophyllum makumensis gen. et sp. nov., from the late Oligocene of the Makum Coalfield, Assam, northeast India, extending the historical range of the family into South Asia. The fossil leaf shows close affinity to Tetramerista glabra Miq. and indicates that the genus was present in the Indian subcontinent during the late Oligocene, suggesting that the modern disjunction in the Tetrameristaceae family likely developed after this time. Further, to test whether this disjunction reflects climatic differentiation or ecological conservatism, we conducted a multivariate climatic analysis using 18 bioclimatic variables from 151 modern occurrence localities. The results reveal substantial macroclimatic overlap among the three genera, indicating broadly conserved climatic tolerances despite their geographic isolation. Integration of CLAMP‐based palaeoclimatic estimates from the late Oligocene Makum with Neogene and modern datasets from northeast India indicates persistently warm and humid conditions with increasing seasonality through time. These findings suggest that the disjunction in Tetrameristaceae is not primarily driven by climatic divergence but by long‐term habitat conservatism and the fragmentation or loss of specialised ecosystems. In particular, the disappearance of Tetramerista from the Indian subcontinent is most plausibly linked to the loss of freshwater peat swamp forests associated with tectonic and landscape reorganisation. This study highlights the role of habitat specialisation, rather than climate alone, in shaping persistent tropical biogeographic disjunctions.