TANIKO Madagascar

Madagascar’s Holocene vertebrate megafauna included giant lemurs, hippopotami, giant tortoises, and the world’s largest birds—the elephant birds [Aepyornithidae, ~500 kg (1)]. This megafauna is now completely extinct, with the largest surviving endemic vertebrates less than 10 kg in body mass (2). Representatives of all of Madagascar’s extinct megafauna are known to have survived into the Holocene (2), with last-occurrence dates for all genera between ~2400 and 500 years before present (B.P.), suggesting that human activities, rather than climatic shifts, were responsible for the extinction of these animals. However, the dynamics of the Malagasy faunal extinction process and the nature of human involvement in driving prehistoric biodiversity loss (for example, overkill versus population attrition, possibly through indirect processes such as habitat degradation or natural climatic change) remain poorly understood due to limited data on human-faunal interactions and the duration of temporal overlap between humans and now-extinct species.

Researchers have sought to understand the process of Holocene biodiversity loss in Madagascar by comparing pre- and post-human eras (2). Archaeological evidence for settled villages dates from 1300 years B.P. onward, with occupation of most of Madagascar’s coasts by 900 years B.P. (3). Archaeological, genetic, and linguistic data all indicate that these colonists were of both Austronesian and East African heritage (4–8). Lake sediment cores indicate substantial ecological change associated with Madagascar’s known late Holocene archaeological period; precipitous drops of the dung fungus Sporormiella demonstrate a significant loss of endemic megafaunal biomass (9), followed by the expansion of grassland savannah evidenced by pollen shifts from C3 to C4 plants and sharp rises in charcoal microparticulates (10–13).

Evidence for the timing of first human arrival in Madagascar during the late Holocene informs how researchers define pre-human or “pristine” ecosystems, frameworks for understanding ecological succession and resilience, and natural baselines for conservation objectives for Madagascar’s threatened biodiversity (13–15). Evidence available in the 1980s to 2010s suggested a first human arrival about 1500 years B.P. However, several lines of evidence have been proposed to suggest a longer period of prehistoric human occupation of Madagascar across the middle to late Holocene. Western coastal rock shelters provide support for regional human presence from ~3000 years B.P. onward, through evidence of protracted subsistence on endemic coastal and marine fauna (16). Butchery traces have been used to understand global human impacts on naïve faunas and to document the spread of prehistoric humans (17–20). Bones of Madagascar’s extinct megafaunal mammals with butchery cut marks but lacking any associated artifacts are also known to predate the widely accepted archaeological settlement period. A Palaeopropithecus ingens radius with cut marks from Taolambiby, southwest Madagascar, has been dated to ~2400 years B.P. (21), and bones of Hippopotamus lemerlei from northwest Madagascar with calibrated radiocarbon dates of 4288 to 4035 years B.P. are reported to show cut marks (22). The paradigm of late human arrival in Madagascar has recently been further challenged by discovery of small assemblages of microlithic tools at sites indicating transient occupation in northern Madagascar (Lakaton’i Anja, Ambohiposa), which have also been dated to up to >4000 years B.P. (23).