Nitrogen isotope (δ¹⁵N) patterns for amino acids in lemur bones are inconsistent with aridity driving megafaunal extinction in south-western Madagascar

Most endemic species with body masses >10 kg on Madagascar went extinct within the past 1000 years. The extent to which human predation, anthropogenic landscape transformation and aridification may separately or together explain this extinction pattern remains controversial. We present nitrogen isotope (δ¹⁵N) values of individual amino acids preserved in bones from now-extinct Pachylemur insignis and extant Propithecus verreauxi from two subfossil sites in south-western Madagascar: Tsirave and Taolambiby. The amino acid-specific approach allows us to identify environmental signals that are otherwise difficult to recognize in bulk collagen δ¹⁵N values. Specifically, we use the δ¹⁵N values of source amino acids (phenylalanine and lysine) as a proxy for habitat aridity between ca. 4000 years ago and present and the spacing of δ¹⁵N values between trophic and source amino acids to quantify trophic levels for these two lemur species. Despite paleoenvironmental evidence for lowering water tables and the expansion of relatively arid savanna between 4000 and 1000 years ago, our isotope data suggest that these lemurs did not live in increasingly arid habitats and did not change their trophic level. Together, our results support the hypothesis that aridity alone did not play a major role in late Holocene megafaunal extinctions in south-western Madagascar.