Solving the woolly mammoth conundrum: amino acid 15N-enrichment suggests a distinct forage or habitat

Rachel Schwartz-Narbonne,Grant Zazula,Fred J. Longstaffe,Jessica Z. Metcalfe

doi:10.1038/srep09791

Abstract

Understanding woolly mammoth ecology is key to understanding Pleistocene community dynamics and evaluating the roles of human hunting and climate change in late Quaternary megafaunal extinctions. Previous isotopic studies of mammoths’ diet and physiology have been hampered by the ‘mammoth conundrum’: woolly mammoths have anomalously high collagen δ15N values, which are more similar to coeval carnivores than herbivores, and which could imply a distinct diet and (or) habitat, or a physiological adaptation. We analyzed individual amino acids from collagen of adult woolly mammoths and coeval species, and discovered greater 15N enrichment in source amino acids of woolly mammoths than in most other herbivores or carnivores. Woolly mammoths consumed an isotopically distinct food source, reflective of extreme aridity, dung fertilization, and (or) plant selection. This dietary signal suggests that woolly mammoths occupied a distinct habitat or forage niche relative to other Pleistocene herbivores.

Highlights

Understanding woolly mammoth ecology is key to understanding Pleistocene community dynamics and evaluating the roles of human hunting and climate change in late Quaternary megafaunal extinctions
The various hypotheses to explain this phenomenon have different implications for our understanding of the now-vanished mammoth steppe ecosystem, woolly mammoth ecology, and related factors that contributed to extirpation of the woolly mammoth in this region
The fact that the δ15NPhe values of woolly mammoths are higher than those of carnivores suggests that the latter consumed herbivores subsisting on less 15N-rich forage than consumed by woolly mammoths

Summary

Introduction

Understanding woolly mammoth ecology is key to understanding Pleistocene community dynamics and evaluating the roles of human hunting and climate change in late Quaternary megafaunal extinctions. Mammoths consumed an isotopically distinct food source, reflective of extreme aridity, dung fertilization, and (or) plant selection. This dietary signal suggests that woolly mammoths occupied a distinct habitat or forage niche relative to other Pleistocene herbivores. While modern Arctic graminoids and forbs from some sites have a δ15N range of –0.3 to +10‰, the average value of these species ranges from ~+1 to ~+4‰16, and still other studies have reported maximum δ15N values for modern sedges of +2‰17 and for modern herbs of +5.3‰18 The majority of these plants, are not sufficiently enriched in 15N to explain the woolly mammoth δ15NBulk values. It has been proposed that woolly mammoths had distinct metabolic processes, such as increased levels of nitrogen recycling associated with winter starvation[22,23] or poor quality food with low protein levels[3,7,8,9,11,13,14,24], or that woolly mammoths engaged in coprophagy[12]

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Results

Conclusion