The stable carbon isotope composition (δ13C) of plant components such as plant wax biomarkers is an important tool for reconstructing past vegetation. Plant wax δ13C is mainly controlled by photosynthetic pathways, allowing for the differentiation of C4 tropical grasses and C3 forests. Proxy interpretations are however complicated by additional factors such as aridity, vegetation density, elevation, and the considerable δ13C variability found among C3 plant species. Moreover, studies on plant wax δ13C in tropical soils and plants have focused on Africa, while structurally different South American savannas, shrublands and forests remain understudied. Here, we analyze the δ13C composition of long-chain n-alkanes and fatty acids from tropical South American soils and leaf litter to assess the isotopic variability in each vegetation type and to investigate the influence of climatic features on δ13C. Rainforests and open vegetation types show distinct values, with rainforests having a narrow range of low δ13C values (n-C29 n-alkane: -34.5 +0.9/-0.6 ‰ ; Suess-effect corrected) allowing for the detection of even minor incursions of savanna into rainforests (13C-enriched). While Cerrado savannas and semi-arid Caatinga shrublands grow under distinctly different climates, they can yield indistinct δ13C values for most compounds. Cerrado soils and litter show pronounced isotopic spreads between the n-C33 and n-C29 alkanes, while Caatinga shrublands show consistent values across the two homologues, thereby enabling the differentiation of these vegetation types. The same multi-homologue isotope analysis can be extended to differentiate African shrublands from savannas.

The assembly of the world’s most biodiverse region, the Neotropics, was traditionally considered the result of long-term environmental stability. Studies gathered during the last decades suggest that environmental “instability” instead, specially the dramatic modifications caused by the uplift of the Andes, was responsible of the Neotropical diversity. Yet a comprehensive understanding has been hindered by a lack of large-scale comparative data across wide phylogenetic and ecological contexts. Here, we evaluate the timing and drivers of Neotropical diversification in a large sample of Neotropical clades: 150 phylogenies (12,524 species) of seed plants and major tetrapods (amphibians, mammals, squamates, and birds). We unveil five trends: (1) biodiversity levels before the Quaternary were comparable (or higher) to those of the present,; (2) half of the clades diversified at constant rates; (3) past environmental variations correlate with diversification changes in 37% of the lineages, but with contrasting responses: (4) birds and mammals diversified extensively during warm periods and global cooling resulted in synchronized slowdowns of diversification; plant diversification generally increased during cooling; and (5) the rise of the Andes mostly impacted amphibians and squamates. Our study suggests that environmental instability over macroevolutionary scales may in fact act as a driving force of Neotropical diversification.