Continental Island Formation and the Archaeology of Defaunation on Zanzibar, Eastern Africa

Abstract

With rising sea levels at the end of the Pleistocene, land-bridge or continental islands were formed around the world. Many of these islands have been extensively studied from a biogeographical perspective, particularly in terms of impacts of island creation on terrestrial vertebrates. However, a majority of studies rely on contemporary faunal distributions rather than fossil data. Here, we present archaeological findings from the island of Zanzibar (also known as Unguja) off the eastern African coast, to provide a temporal perspective on island biogeography. The site of Kuumbi Cave, excavated by multiple teams since 2005, has revealed the longest cultural and faunal record for any eastern African island. This record extends to the Late Pleistocene, when Zanzibar was part of the mainland, and attests to the extirpation of large mainland mammals in the millennia after the island became separated. We draw on modeling and sedimentary data to examine the process by which Zanzibar was most recently separated from the mainland, providing the first systematic insights into the nature and chronology of this process. We subsequently investigate the cultural and faunal record from Kuumbi Cave, which provides at least five key temporal windows into human activities and faunal presence: two at the end of the Last Glacial Maximum (LGM), one during the period of post-LGM rapid sea level rise and island formation, and two in the late Holocene (Middle Iron Age and Late Iron Age). This record demonstrates the presence of large mammals during the period of island formation, and their severe reduction or disappearance in the Kuumbi Cave sequence by the late Holocene. While various limitations, including discontinuity in the sequence, problematize attempts to clearly attribute defaunation to anthropogenic or island biogeographic processes, Kuumbi Cave offers an unprecedented opportunity to examine post-Pleistocene island formation and its long-term consequences for human and animal communities.

Coastal Subsistence, Maritime Trade, and the Colonization of Small Offshore Islands in Eastern African Prehistory

“…Sorghum and pearl millet have also been reported from EIA sites in Mikindani on the southern Tanzanian coast (Pawlowicz 2011). This combined evidence demonstrates that migrating early farming communities most likely carried crops with them to eastern Africa, including to the coastal region.…”

Reconstructing Prehistoric African Population Structure

“…4353). It was recovered from context 1011, in association with local Tana Tradition ceramics typical of the MIA, moderately-sized limestone lithic artifacts, and diverse wild game animals, but no additional human remains (Prendergast et al, 2016). The specimen is directly dated to 1370–1303 calBP (1479 ± 23 BP, OxA-31427), thus placing it at the beginning of the MIA phase.…”

The Middle/Later Stone Age transition and cultural dynamics of late Pleistocene East Africa

“…The rainforest is also subject to extensive contraction, fragmentation, or expansion caused by increases or decreases in rainfall that may have contributed to intermittent hominin occupation of its margins . Nearshore islands such as Zanzibar appear to have been occupied as early as the LGM ~18–26 ka, possibly aided by lowered sea level . Although taxonomically dominated by extant taxa (Table ), fossil fauna at a number of archeological sites indicate generally more arid conditions throughout the region for much of the Late Pleistocene.…”

“…East Africa is a useful region to study because of its relatively large number of archeological sequences that sample the MSA/LSA transition, including Enkapune ya Muto, Kisese II, multiple sites at Lukenya Hill, Magosi, Magubike, Mtongwe, Mumba, Nasera, Panga ya Saidi, and Shurmai; individual MSA and LSA sites in the Lake Victoria basin, Olduvai Gorge, and Kuumbi Cave provide additional constraints on the transition but lack extensive stratigraphic sequences or large sample sizes sufficient to assess change over time (Table ). East Africa as defined here encompasses ~1.77 million km 2 and can serve as a useful point of comparison for other similarly sized regions that also preserve MSA/LSA sequences, such as Ethiopia and the Horn of Africa (~1.88 million km 2 ), as well as southern Africa (~2.09 million km 2 ) …”

“…44 Nearshore islands such as Zanzibar appear to have been occupied as early as the LGM~18-26 ka, possibly aided by lowered sea level. 47,48 Although taxonomically dominated by extant taxa (Table 1), fossil fauna at a number of archeological sites indicate generally more arid conditions throughout the region for much of the Late Pleistocene.…”