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Taxonomic and taphonomic data on 236 fossil bird bone specimens are applied to paleolandscape models and reconstructions developed by the Olduvai Landscape Paleoanthropology Project (OLAPP) for Late Pliocene (1.84 Ma) hominid bearing deposits in the FLK Complex at Olduvai Gorge, Tanzania. Shorebirds dominate the avifauna but the occurrence and densities of different avian ecotypes vary across the landscape in ways that corroborate OLAPP reconstructions of wetland, peninsular and riverine landscape facets in this area of the paleo-Lake Olduvai Basin. Taphonomic profiles are based on observations of modern bird bone in similar environments of Tanzania. The taphonomy suggests habitat patchiness within these delineated landscape facets. Results support the use of fossil bird assemblages, even small assemblages thereof, for aiding in and refining paleoenvironmental reconstructions. PrassacK, Kari a., 2010. Late Pliocene avifauna from the hominid-bearing Zinjanthropus land surface at Olduvai Gorge, Tanzania. In Proceedings of the VII International Meeting of the Society of Avian Paleontology and Evolution, ed. W.E. Boles and T.H. Worthy. Records of the Australian Museum 62(1): 185–192. Olduvai Gorge is a bifurcated valley in the Eastern Serengeti Plains, part of the western margin of the Eastern Rift Valley of northern Tanzania. The Ngorongoro Volcanic Highlands to the south and east contributed ca. 100 m of volcaniclastic sediments spanning the last two million years at Olduvai (Hay, 1976). This produced extensive, fossiliferous deposits, dating from the late Pliocene through more recent times, which were later exposed by tectonic uplift and down-cutting that created the Gorge. Olduvai Gorge is best known for its paleoanthropological richness, beginning with discoveries by Louis and Mary Leakey (e.g., L.S.B. Leakey, 1965; M.D. Leakey, 1971) of early hominid fossils in association with primitive, Oldowan stone tools. Since 1989, excavations at Olduvai have been undertaken by the Olduvai Landscape Paleoanthropology Project (OLAPP), an international and interdisciplinary team whose goals are to understand the subsistence ecology of these early hominids through detailed reconstructions of the paleoenvironments in which they made and used stone tools and butchered animal carcasses (e.g., Blumenschine & Masao, 1991; Peters & Blumenschine, 1995; Blumenschine & Peters, 1998; Blumenschine et al., 2008). OLAPP uses a landscape paleoanthropology approach in which numerous, relatively small scale excavations are placed across exposed portions (ca. 130 km2) of the Olduvai Basin. Trench locations are based on accessibility of the target stratigraphic unit-regardless of artifact densities observed to have been eroded to the surface. This method produces samples of stone tools, fossils and other paleoenvironmental indicators across a full range of paleolandscape facets for a given depositional sequence. A recent focus of OLAPP has been to develop landscape samples between and beyond two important Late Pliocene (1.84 Ma) sites in the FLK Complex (Fig. 1): Level 22 at 186 Records of the Australian Museum (2010) Vol. 62 FLK and Level 1 at FLK NN. These sites were excavated by the Leakeys in 1959–1962 and are known for their dense concentrations of Oldowan stone artifacts and vertebrate fossils, including hominid remains such as the type specimens of Homo habilis and Paranthropus (syn. Zinjanthropus) boisei, (L.S.B. Leakey, 1959; L.S.B. Leakey et al., 1964; Tobias, 1967). The FLK Complex spans a distance of ca. 0.5 km along the eastern lake margin, or floodplain, of paleo-Lake Olduvai, a closed, shallow, saline and alkaline lake that fluctuated in size between a maximum diameter of ca. 25 km during wet periods, and a perennial portion of ca. 10 km diameter during dry periods (Hay, 1976). The deposits of interest occur on what is referred to as the Zinjanthropus land surface, named for the famous Zinjanthropus skull discovered in 1959 from FLK, Level 22 (L.S.B. Leakey, 1959). This land surface is stratified between two volcanic tuffs, IB and IC, the latter of which buried and preserved the Zinjanthropus land surface, allowing for geologically precise dating of the Zinjanthropus land surface to landscape formation between 1.845 + 0.002 Ma and 1.839 + 0.005 Ma (based on dates in Blumenschine et al., 2003). OLAPP has identified several paleolandscape facets along this half-kilometer stretch of the Zinjanthropus land surface (Fig. 1) on the basis of sedimentary facies analysis and supported by botanical and vertebrate fossils (Blumenschine et al., in press). These landscape facets include a 0.5–1.0 m high, lightly wooded Peninsula in the area of FLK, with a very low-gradient River Channel or Spillway to the south (FLK S) and a freshwater Wetland (FLK N and FLK NN), directed towards the lake shoreline to the north. The Wetland is divided into two sub-facets, an expansive Wetland Interior (FLK NN), located along the eastern lake margin, and the Wetland Edge (FLK N), a narrow zone occurring at the ecotone of the Wetland and Peninsula. These four landscape facets delimit for the first time the mosaic of marshland, woodland, bushland and grass/sedgeland environments evident from previous analyses of mammalian faunas from the two Leakey sites (e.g., Plummer & Bishop, 1994; Kappelman et al., 1997; Fernandez-Jalvo et al., 1998), as Figure 1. Schematic map depicting the spatial orientation of three major landscape facets in the FLK Complex, during Middle Bed I times (1.8 Ma). Landscape reconstructions are based on botanical, sedimentological and paleontological material recovered by OLAPP in the areas of FLK S (Tr. 143, 146, 148), FLK (Tr. 138, 140, 141), FLK N (Tr. 137, 144, 142, 147), and FLK NN (Tr. 134, 135, 145) (Blumenschine et al., in press) and by the M.D. Leakey’s (1971) at FLK (Level 22) and FLK NN (Level 1). Birds were recovered from all trenches with the exception of 134, 141, 143 and 148. well as OLAPP’s results (Blumenschine et al., in press). The fossil avifauna from the Zinjanthropus land surface contributes two classes of paleoecological information to these landscape reconstructions. One is the taxonomic and ecotypic composition of avifaunal assemblages from each landscape facet. A second is comprised of taphonomic data from the same assemblages, the interpretation of which are guided by my observations in modern salinealkaline lake environments in the Rift Valley of northern Tanzania (Prassack, dissertation in prep.). Here, I report these taxonomic and taphonomic data, providing details not reported in Blumenschine et al. (in press). Materials and methods Fossil bird bones (NISP [number of identified specimens present] = 236) were recovered from the Zinjanthropus land surface in nine of the thirteen trenches excavated by OLAPP during the 2006–2008 field seasons. Excavations were made by skilled OLAPP field workers using picks to break up the matrix followed by dry sieving using a 5 mm wire mesh sieve. For trenches 144–147, blocks of clay were taken back to the base camp where they were spread on plastic sheets, wetted, and allowed to dry in several cycles to break up the matrix, allowing the recovery of micro-faunal remains with low risk of breakage and higher likelihood of recovery. Taxonomic identifications are conservative and based on comparison to multiple osteological specimens from a full range of relevant modern taxa housed at the Florida Museum of Natural History and American Museum of Natural History. Specimens were not piece-plotted during excavation, such that in–situ specimen associations could not be made. As a result, I made no attempt to identify phalanges or vertebrae beyond that of Aves. Shorebird identifications are to the family level only until a more comprehensive comparative analysis can be made of these specimens. Ericson’s (1987) formula for measuring wing versus leg abundance is used to determine if taphonomic processes affected avian skeletal part survivorship and how this may have differed across the landscape. In this formula, the NISP of wing elements (humerus + ulna + carpometacarpus) is divided by the sum of wing and leg (femur + tibiotarsus + tarsometatarsus) elements, such that a percentage deviation of the quotient from 50% suggests taphonomic bias in skeletal part survivorship. Taphonomic analysis involved careful examination of each specimen under a 100 W lamp using 10–20× magnification hand lenses. Flaking, cracking and corrosion of bone (Fig. 2) was used to assign bone to subaerial weathering stages (Table 2) following Behrensmeyer (1978) with proper adjustment for birds (Behrensmeyer et al., 2003). Evidence of carnivore tooth marks (Fig. 3a–b, Blumenschine et al., 1996), rodent gnawing (Fig. 3c), medullary bone (Fig. 3d), and trample marks (Behrensmeyer et al., 1986; Fiorillo, 1989) was also noted. Bioerosion, defined here as the macroscopic alteration of bone’s outer cortical surface by algae, fungi, aquatic invertebrates and/or insects (see Blumenschine et al., 2007 for review), was diverse and observed on specimens from all facets. Data on bioerosion will be presented in a forthcoming manuscript, comparing fossil marks to those observed during modern landscape studies in Tanzania (Prassack, dissertation in prep.). Prassack: Late Pliocene fossil birds from Olduvai Gorge 187 Figure 2. Flaking (a), cracking (b), and corrosion (c) to bird bone interpreted as the result of exposure to subaerial weathering. Scale bars are 5 mm (a), 1 mm (b), and 5 mm (c). Figure 3. Taphonomic analysis of the FLK Complex birds revealed modifications by carnivores including (a) small tooth pits and (b) scores, in all landscape facets. Rodent-gnawed bones (c) also occurred in all facets, while medullary bone (d) was limited to the Wetland Interior and Wetland Edge. Scale bars are 1 mm. Results Table 1 lists the 236 fossil bird specimens recovered by OLAPP in the FLK Complex. The vast majority of specimens (70%)

records of the australian museum

Late Pliocene avifauna from the hominid-bearing Zinjanthropus land surface at Olduvai Gorge, Tanzania. In Proceedings of the VII International Meeting of the Society of Avian Paleontology and Evolution, ed. W.E. Boles and T.H. Worthy