Supplementary file S1. from Dietary isotopes of Madagascar's extinct megafauna reveal Holocene browsing and grazing guilds

Megafauna plays a disproportionate role in developing and maintaining their biomes, by regulating plant dispersal, community structure and nutrient cycling. Understanding the ecological roles of extinct megafaunal communities, for example through dietary reconstruction using isotope analysis, is necessary to determine pre-human states and set evidence-based restoration goals. We use <i>δ</i>¹³C and <i>δ</i>¹⁵N isotopic analyses to reconstruct Holocene feeding guilds in Madagascar's extinct megaherbivores, which included elephant birds, hippopotami and giant tortoises that occurred across multiple habitats and elevations. We compare isotopic data from seven taxa and two elephant bird eggshell morphotypes against contemporary regional floral baselines to infer dietary subsistence strategies. Most taxa show high consumption of C₃ and/or CAM plants, providing evidence of widespread browsing ecology. However, <i>Aepyornis hildebrandti</i>, an elephant bird restricted to the central highlands region, has isotope values with much higher <i>δ</i>¹³C values than other taxa. This species is interpreted as having obtained up to 48% of its diet from C₄ grasses. These findings provide new evidence for distinct browsing and grazing guilds in Madagascar's Holocene megaherbivore fauna, with implications for past regional distribution of ecosystems dominated by endemic C₄ grasses.

巨型动物群在构建与维持其栖息的生物群系过程中，发挥着远超自身生物量占比的关键作用，具体通过调控植物传播、群落结构与养分循环来实现。若要确定人类活动前的生态系统状态，并制定基于实证的修复目标，就需要理解已灭绝巨型动物群落的生态角色——例如通过同位素分析开展饮食结构重建。本研究利用碳稳定同位素（δ¹³C）与氮稳定同位素（δ¹⁵N）分析，重建马达加斯加已灭绝巨型草食动物的全新世觅食功能群，这些动物涵盖曾广泛分布于多种生境与海拔带的象鸟、河马与巨龟。我们将7个分类单元与2种象鸟蛋壳形态型的同位素数据，与当代区域植物基线数据进行对比，以推断其饮食生存策略。多数分类单元均表现出对C₃植物及/或CAM植物的高摄取比例，证明其普遍以啃食型生态位生存。然而，仅分布于中部高地的希氏象鸟（*Aepyornis hildebrandti*），其同位素值的δ¹³C显著高于其他类群。研究推断该物种约48%的饮食来源为C₄草本植物。上述发现为马达加斯加全新世巨型草食动物群落中存在独特的啃食与放牧功能群提供了新的实证依据，同时也为特有C₄草本主导的古生态系统的既往区域分布格局提供了重要启示。