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

Abstract

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 (d 15 N) 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 d 15 N values. Specifically, we use the d 15 N 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 d 15 N 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. #

A multimillennial climatic context for the megafaunal extinctions in Madagascar and Mascarene Islands

“…Second, the timing and rate of megafaunal extinctions are imprecisely constrained. The current compilations of 14 C dates from subfossil vertebrates suggest that most megafaunal species went extinct after ~1000 yr B.P. (9), and there are no credible 14 C dates for any of the extinct species younger than ~500 yr B.P.…”

“…References for bomb peak calibration in SH zone 1-2 (the area between ~10°S and 90°S over the Indian Ocean) (50) and SHCal13 (51), calibrated radiocarbon ages of subsamples from the surface and at 0.4-mm depth, were obtained using BetaCal 3.21 and the high-probability density range method (52). For other 14 C dates, an anchor point of known age (720 ± 34 yr B.P.) at 15.5 mm (blue triangle), the LAVI-15-7  13 C profile, and SHCal13 (51) were used to construct the age model.…”

A new late Pleistocene subfossil site (Tsaramody, Sambaina basin, central Madagascar) with implications for the chronology of habitat and megafaunal community change on Madagascar's Central Highlands

“…Burney, , , ; Burney & Flannery, ; Burney et al ., , ; Godfrey & Irwin, ; Goodman & Jungers, ; MacPhee et al ., ). However, the importance of climate change has been challenged (Burns et al ., ; Crowley et al ., ; Godfrey et al ., ; Hixon et al ., ). To resolve this question, it is critical to track changes in faunal composition through recent geological time, paying particular attention to how distributions were affected by climate before human arrival.…”

“…Megafaunal extinction is widely believed to have been induced by humans, either directly (via hunting) or indirectly (via landscape transformation), aided by Late Pleistocene and Holocene climatic change (e.g. 2016;Crowley et al, 2017;Godfrey et al, 2019;Hixon et al, 2018). To resolve this question, it is critical to track changes in faunal composition through recent geological time, paying particular attention to how distributions were affected by climate before human arrival.…”

Potential evolutionary body size reduction in a Malagasy primate (Propithecus verreauxi) in response to human size-selective hunting pressure

“…There are reports of intentional human processing marks on lemur bones in southwest Madagascar dating to ~2,300 years BP [11,18,19]. Human harvesting pressures, perhaps including preferential hunting of larger animals, have often been discussed as potential contributing factors in population declines and eventual extinctions of the island's megafauna [18,[20][21][22][23]. Now, no surviving endemic terrestrial vertebrate species on Madagascar has a body mass larger than 10 kg [24].…”