Mid-Holocene aridity recorded in pygmy hippo and giant tortoise bone from southwest Madagascar

Aridity can exacerbate threats to endemic biodiversity, and arid intervals during the last couple of millennia may have contributed to endemic large herbivore extinctions on Madagascar. However, regional palaeoclimate records spanning multiple millennia are limited, and the tolerance of extinct taxa to past water scarcity is poorly known. To infer changes in the diet and habitat aridity of extinct pygmy hippos and giant tortoises during approximately 6000-1000 years ago, I used carbon and nitrogen isotope (δ¹³C and δ¹⁵N) data from 49 directly radiocarbon-dated bones collected around Tampolove, southwest Madagascar. Fluctuations in bone δ¹⁵N values through time in both species indicate tolerance of dry habitat during intermittent drying trends, including around a dry period known as the '4.2 ka event'. However, taxon-specific differences in the covariance of bone δ¹³C and δ¹⁵N values suggest that the diets of pygmy hippos and giant tortoises changed in different ways during these past arid intervals. This suggests that past aridification had different effects on these taxa. Thus, I argue that hypotheses for past extinction that involve a synergy among climate drying and forest clearance, hunting and biological invasion must consider taxon-specific responses to past aridity.