Erik J. de Boer

A deadly cocktail: How a drought around 4200 cal. yr BP caused mass mortality events at the infamous ‘dodo swamp’in Mauritius

Analyses of pollen, diatoms, XRF geochemistry, and pigments provide a unique window into how an insular ecosystem in Mauritius responded to an extreme drought event 4200 years ago. We provide a reconstruction of regional vegetation change and local wetland development under influence of sea level rise and inferred climate change between 4400 and 4100 cal. yr BP. Our multi-proxy data evidence a severe drought between 4190 and 4130 cal. yr BP, which ultimately led to mass mortality of larger vertebrates, including two species of giant tortoises and dodos in a <2-ha region. This prolonged drought around the Indian Ocean is recorded in many regions dependent on monsoon precipitation and is suggested to cause the collapse of human societies in East Africa and India. We demonstrate a direct relation between the mass mortality events in the Mare aux Songes (MAS) rock valley and the 4200 cal. yr BP drought. MAS represents a fresh water source that attracted and concentrated vertebrates. Abrupt increased aridity induced regional fires on Mauritius and caused decreased water levels, and a shrinking water surface resulting in further concentration of the animals in this coastal site. Upconing of the saline wedge underlying the fresh water source induced progressive salinization. The excrements of the animals produced hypertrophic conditions that, combined with salinization and high temperatures, created a suitable environment for potentially toxic cyanobacteria. These factors led to a deadly cocktail, resulting in the death of 100,000s of vertebrates by intoxication, dehydration, trampling, and miring, and promoted a unique conservation of fossils. The ‘4.2 ka megadrought’ likely induced similar bottlenecks elsewhere in the SW Indian Ocean region.

Island biodiversity conservation needs palaeoecology

The discovery and colonization of islands by humans has invariably resulted in their widespread ecological transformation. The small and isolated populations of many island taxa, and their evolution in the absence of humans and their introduced taxa, mean that they are particularly vulnerable to human activities. Consequently, even the most degraded islands are a focus for restoration, eradication, and monitoring programmes to protect the remaining endemic and/or relict populations. Here, we build a framework that incorporates an assessment of the degree of change from multiple baseline reference periods using long-term ecological data. The use of multiple reference points may provide information on both the variability of natural systems and responses to successive waves of cultural transformation of island ecosystems, involving, for example, the alteration of fire and grazing regimes and the introduction of non-native species. We provide exemplification of how such approaches can provide valuable information for biodiversity conservation managers of island ecosystems.

A review of the dodo and its ecosystem: insights from a vertebrate concentration Lagerstätte in Mauritius

ABSTRACT The dodo Raphus cucullatus Linnaeus, 1758, an extinct and flightless, giant pigeon endemic to Mauritius, has fascinated people since its discovery, yet has remained surprisingly poorly known. Until the mid-19th century, almost all that was known about the dodo was based on illustrations and written accounts by 17th century mariners, often of questionable accuracy. Furthermore, only a few fragmentary remains of dodos collected prior to the birds extinction exist. Our understanding of the dodos anatomy was substantially enhanced by the discovery in 1865 of subfossil bones in a marsh called the Mare aux Songes, situated in southeastern Mauritius. However, no contextual information was recorded during early excavation efforts, and the majority of excavated material comprised larger dodo bones, almost all of which were unassociated. Here we present a modern interdisciplinary analysis of the Mare aux Songes, a 4200-year-old multitaxic vertebrate concentration Lagerstätte. Our analysis of the deposits at this site provides the first detailed overview of the ecosystem inhabited by the dodo. The interplay of climatic and geological conditions led to the exceptional preservation of the animal and associated plant remains at the Mare aux Songes and provides a window into the past ecosystem of Mauritius. This interdisciplinary research approach provides an ecological framework for the dodo, complementing insights on its anatomy derived from the only associated dodo skeletons known, both of which were collected by Etienne Thirioux and are the primary subject of this memoir. Citation for this article: Rijsdijk, K. F., J. P. Hume, P. G. B. de Louw, H. J. M. Meijer, A. Janoo, E. J. de Boer, L. Steel, J. de Vos, L. G. van der Sluis, H. Hooghiemstra, F. B. V. Florens, C. Baider, T. J. J. Vernimmen, P. Baas, A. H. van Heteren, V. Rupear, G. Beebeejaun, A. Grihault, J. van der Plicht, M. Besselink, J. K. Lubeek, M. Jansen, S. J. Kluiving, H. Hollund, B. Shapiro, M. Collins, M. Buckley, R. M. Jayasena, N. Porch, R. Floore, F. Bunnik, A. Biedlingmaier, J. Leavitt, G. Monfette, A. Kimelblatt, A. Randall, P. Floore, and L. P. A. M. Claessens. 2015. A review of the dodo and its ecosystem: insights from a vertebrate concentration Lagerstätte in Mauritius; pp. 3–20 in L. P. A. M. Claessens, H. J. M. Meijer, J. P. Hume, and K. F. Rijsdijk (eds.), Anatomy of the Dodo (Raphus cucullatus L., 1758): An Osteological Study of the Thirioux Specimens. Society of Vertebrate Paleontology Memoir 15. Journal of Vertebrate Paleontology 35(6, Supplement).