Paleoecology of the Serengeti during the Oldowan-Acheulean transition at Olduvai Gorge, Tanzania: The mammal and fish evidence

Abstract

Eight years of excavation work by the Olduvai Geochronology and Archaeology Project (OGAP) has produced a rich vertebrate fauna from several sites within Bed II, Olduvai Gorge, Tanzania. Study of these as well as recently re-organized collections from Mary Leakey's 1972 HWK EE excavations here provides a synthetic view of the faunal community of Olduvai during Middle Bed II at ∼1.7-1.4 Ma, an interval that captures the local transition from Oldowan to Acheulean technology. We expand the faunal list for this interval, name a new bovid species, clarify the evolution of several mammalian lineages, and record new local first and last appearances. Compositions of the fish and large mammal assemblages support previous indications for the dominance of open and seasonal grassland habitats at the margins of an alkaline lake. Fish diversity is low and dominated by cichlids, which indicates strongly saline conditions. The taphonomy of the fish assemblages supports reconstructions of fluctuating lake levels with mass die-offs in evaporating pools. The mammals are dominated by grazing bovids and equids. Habitats remained consistently dry and open throughout the entire Bed II sequence, with no major turnover or paleoecological changes taking place. Rather, wooded and wet habitats had already given way to drier and more open habitats by the top of Bed I, at 1.85-1.80 Ma. This ecological change is close to the age of the Oldowan-Acheulean transition in Kenya and Ethiopia, but precedes the local transition in Middle Bed II. The Middle Bed II large mammal community is much richer in species and includes a much larger number of large-bodied species (>300 kg) than the modern Serengeti. This reflects the severity of Pleistocene extinctions on African large mammals, with the loss of large species fitting a pattern typical of defaunation or 'downsizing' by human disturbance. However, trophic network (food web) analyses show that the Middle Bed II community was robust, and comparisons with the Serengeti community indicate that the fundamental structure of food webs remained intact despite Pleistocene extinctions. The presence of a generalized meat-eating hominin in the Middle Bed II community would have increased competition among carnivores and vulnerability among herbivores, but the high generality and interconnectedness of the Middle Bed II food web suggests this community was buffered against extinctions caused by trophic interactions.

From the Oldowan to the Acheulean at Olduvai Gorge, Tanzania – An introduction to the special issue

“…Assemblage IIB sees a decrease in the number of C 3 and mixed feeders, and an increase on the abrasiveness of the diet . Nonetheless, both stable isotopes and tooth wear analyses report no major changes in hydrology and vegetation across the sequence , and thus support results by Bibi et al (2018) on the structural continuity of large mammal communities.…”

“…Papers on the stratigraphy and geochronology of Bed II Stanistreet et al ., 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2018) compile data obtained from all trenches excavated, plus additional information from natural outcrop logging and surveys. Papers on the paleoecological reconstruction of Bed II (Prassack et al, 2018;Bibi et al, 2018;Uno et al, 2018) also use all OGAP's materials (i.e., all fossils from 57 trenches through Bed II) as the main dataset, which in this case deserves special mention as they are almost exclusively assemblages derived from excavation, rather than surface collection. One of the papers on the archaeological record (McHenry and de la Torre, 2018) also includes materials from several of the localities sampled by OGAP, but the rest (de la Torre and Mora, 2018a, b; de la Torre et al, 2018a, b;Rivals et al, 2018;Arroyo and de la Torre, 2018) focus on two of the archaeological sites excavated by OGAP, namely HWK EE and EF-HR.…”

Soil and Plant Phytoliths from the Acacia-Commiphora Mosaics at Oldupai Gorge (Tanzania)

“…In East Africa, the transition to arid-adapted woodlands and grasslands over the last two million years has been documented in pedogenic carbonates (Cerling et al, 1988;Levin et al, 2004Levin et al, , 2011Quinn et al, 2007), mammal, bird, and fish fossils (Bibi and Kiessling, 2015;Bibi et al, 2018;Prassack et al, 2018), micro-and macrobotanical remains like pollen, phytoliths, and wood (Bonnefille, 1982(Bonnefille, , 1995Barboni et al, 1999), and stable isotopes of hydrogen and carbon from leaf wax lipid biomarkers (Magill et al, 2013a, b;Uno et al, 2016;Lupien et al, 2018).…”

“…Multiple proxies indicate that during the last two million years the East African climate changed, triggering a shift in its plant landscape from forested ecosystems to open woodland/grassland mosaics. These proxies include paleosol carbonates (Cerling et al, 1988;Levin et al, 2004;Quinn et al, 2007;Levin et al, 2011), vertebrates (Bibi and Kiessling, 2015;Bibi et al, 2018;Prassack et al, 2018), palaeobotanical remains (Bonnefille, 1984(Bonnefille, , 1995, and stable isotopes (Magill et al, 2013a, b;Uno et al, 2016;Lupien et al, 2018). This environmental transformation led to the widespread occurrence of a plant landscape characterized by Acacia-Commiphora woodland (White, 1983), and corresponds with key changes in hominin evolution and ecology (e.g.…”

Soil and plant phytoliths from theAcacia-Commiphoramosaics at Oldupai Gorge (Tanzania)

“…Multiple proxies indicate that during the last two million years the East African climate changed, triggering a shift in its plant landscape from forested ecosystems to open woodland/grassland mosaics. These proxies include paleosol carbonates (Cerling, Bowman & O’Neil, 1988; Levin et al, 2004; Quinn et al, 2007; Levin et al, 2011), vertebrates (Bibi & Kiessling, 2015; Bibi et al, 2018; Prassack et al, 2018), palaeobotanical remains (Bonnefille, 1984; Bonnefille, 1995), and stable isotopes (Magill, Ashley & Freeman, 2013a; Magill, Ashley & Freeman, 2013b; Uno, Polissar & Jackson, 2016; Lupien et al, 2018). This environmental transformation led to the widespread occurrence of a plant landscape characterized by Acacia-Commiphora woodland (White, 1983), and corresponds with key changes in hominin evolution and ecology (e.g., Ravelo et al, 2004; Lepre et al, 2011; Beyene et al, 2013).…”