The first Miocene fossils from coastal woodlands in the southern East African Rift.

The Miocene was a key time in the evolution of African ecosystems witnessing the origin of the African apes and the isolation of eastern coastal forests through an expanding arid corridor. Until recently, however, Miocene sites from the southeastern regions of the continent were unknown. Here, we report the first Miocene fossil teeth from the shoulders of the Urema Rift in Gorongosa National Park, Mozambique. We provide the first 1) radiometric ages of the Mazamba Formation, 2) reconstructions of paleovegetation in the region based on pedogenic carbonates and fossil wood, and 3) descriptions of fossil teeth. Gorongosa is unique in the East African Rift in combining marine invertebrates, marine vertebrates, reptiles, terrestrial mammals, and fossil woods in coastal paleoenvironments. The Gorongosa fossil sites offer the first evidence of woodlands and forests on the coastal margins of southeastern Africa during the Miocene, and an exceptional assemblage of fossils including new species.

Olduvai's oldest Oldowan.

Previously, Olduvai Bed I excavations revealed Oldowan assemblages <1.85 Ma, mainly in the eastern gorge. New western gorge excavations locate a much older ∼2.0 Ma assemblage between the Coarse Feldspar Crystal Tuff (∼2.015 Ma) and Tuff IA (∼1.98 Ma) of Lower Bed I, predating the oldest eastern gorge DK assemblage below Tuff IB by ∼150 kyr. We characterize this newly discovered fossil and artifact assemblage, adding information on landscape and hominin resource use during the ∼2.3-2.0 Ma period, scarce in Oldowan sites. Assemblage lithics and bones, lithofacies boundaries, and phytolith samples were surveyed and mapped. Sedimentological facies analysis, tephrostratigraphic and sequence stratigraphic principles were applied to reconstruct paleoenvironments and sedimentary processes of sandy claystone (lake), sandstone (fluvial), and sandy diamictite (debris flow) as principal lithofacies. Artifacts, sized, weighed, categorized, were examined for petrography, retouch, and flake scar size. Taxonomic classifications and taphonomic descriptions of faunal remains were made, and phytoliths were categorized based on reference collections. Lithics are dominantly quartzite, mainly debitage and less frequently simple cores, retouched pieces, and percussors. Well-rounded spheroids and retouched flakes are rare. Identifiable taxa, Ceratotherium cf. simum (white rhinoceros) and Equus cf. oldowayensis (extinct zebra), accord with nearby open savanna grasslands, inferred from C3 grass, mixed and/or alternating with C4 grass-dominated phytolith assemblages. Palms, sedges, and dicots were also identified from phytoliths. Diatoms and sponge spicules imply nearby freshwater. The assemblage accumulated at the toe of a Ngorongoro Volcano-sourced fan-delta apron of stacked debris flows, fluvials, and tuffs, preserving fossil tree stumps and wooded grassland phytoliths farther upfan. It formed after the climax of Ngorongoro volcanic activity during a Paleolake Olduvai lowstand and was then buried and preserved by lacustrine clays, marking the first of two lake transgressions, signifying wetter climates. Orbital precessional lake cycles were superposed upon multimillennial (∼4.9 kyr) lake fluctuations.

The first Loranthaceae fossils from Africa.

An ongoing re-investigation of the early Miocene Saldanha Bay (South Africa) palynoflora, using combined light and scanning electron microscopy (single grain method), is revealing several pollen types new to the African fossil record. One of the elements identified is Loranthaceae pollen. These grains represent the first and only fossil record of Loranthaceae in Africa. The fossil pollen grains resemble those produced by the core Lorantheae and are comparable to recent Asian as well as some African taxa/lineages. Molecular and fossil signals indicate that Loranthaceae dispersed into Africa via Asia sometime during the Eocene. The present host range of African Loranthaceae and the composition of the palynoflora suggest that the fossil had a range of potential host taxa to parasitise during the early Miocene in the Saldanha Bay region.

Pleistocene fossil woods from the Okote Member, site FwJj 14 in the Ileret region, Koobi Fora Formation, northern Kenya.

On the eastern side of Lake Turkana in northern Kenya are extensive Plio-Pleistocene deposits containing a rich diversity of fossil mammals, hominins and flora within the radiometrically dated tuffaceous, lacustrine and fluvial sequence. Reconstruction of this landscape and paleoenvironment are part of an ongoing multinational and multidisciplinary human evolution project in the eastern Turkana Basin. Today there is a huge lake in the Rift Valley but it has fluctuated since the early Pliocene. Silicified wood is fairly common in some areas of the Koobi Fora Formation. One such site is FwJj 14E, alongside one of the tributaries of the Ileret River. Hominin hand and arm bones have been excavated from here in the Okote Member and dated at 1.56-1.36 Ma. The fossils are associated with hominin and bovid footprints. Sixty of the over 100 wood specimens collected have been sectioned and studied. In general the woods have large vessels and an average vulnerability index of 40, which implies a mesic megathermal environment with no water stress. Taxonomically the woods belong to large African families: Caesalpiniaceae (Didelotia idae), Combretaceae (Anogeissus sp.), Putranjivaceae (Euphorbiaceae; Drypetes sp.), Lamiaceae (cf Premna sp.), Malvaceae (Heritiera sp.) and Sapindaceae (Sapindoxylon sp.). Most of these taxa do not occur in the area today because now it is much drier and the local vegetation is predominantly Acacia-Commiphora-Salvadora shrubland. The reconstruction of the paleovegetation supports the interpretation from the fauna, namely, a tall riverine forest with shady refuge trees, possibly some edible fruits, and wooded grassland and more open bushland in the vicinity.

X-rays and virtual taphonomy resolve the first Cissus (Vitaceae) macrofossils from Africa as early-diverging members of the genus.

PREMISE OF THE STUDY: Fossilized seeds similar to Cissus (Vitaceae) have been recognized from the Miocene of Kenya, though some were previously assigned to the Menispermaceae. We undertook a comparative survey of extant African Cissus seeds to identify the fossils and consider their implications for the evolution and biogeography of Cissus and for African early Miocene paleoenvironments. METHODS: Micro-computed tomography (µCT) and synchrotron-based X-ray tomographic microscopy (SRXTM) were used to study seed morphology and anatomy. Virtual taphonomy, using SRXTM data sets, produced digital fossils to elucidate seed taphonomy. Phylogenetic relationships within Cissus were reconstructed using existing and newly produced DNA sequences for African species. Paleobiology and paleoecology were inferred from African nearest living relatives. KEY RESULTS: The fossils were assigned to four new Cissus species, related to four modern clades. The fossil plants were interpreted as climbers inhabiting a mosaic of riverine woodland and forest to more open habitats. Virtual taphonomy explained how complex mineral infill processes concealed key seed features, causing the previous taxonomic misidentification. Newly sampled African species, with seeds most similar to the fossils, belong to four clades within core Cissus, two of which are early diverging. CONCLUSIONS: Virtual taphonomy, combined with X-ray imaging, has enabled recognition of the first fossil Cissus and Vitaceae from Africa. Early-divergent members of the core Cissus clade were present in Africa by at least the early Miocene, with an African origin suggested for the Cissus sciaphila clade. The fossils provide supporting evidence for mosaic paleoenvironments inhabited by early Miocene hominoids.

In situ ∼2.0 Ma trees discovered as fossil rooted stumps, lowermost Bed I, Olduvai Gorge, Tanzania.

The discovery of fossil rooted tree stumps in lowermost Lower Bed I from the western Olduvai Basin, Tanzania, age-bracketed by the Naabi Ignimbrite (2.038 ± 0.005 Ma) and Tuff IA (1.88 ± 0.05 Ma), provides the first direct, in situ, and to date oldest evidence of living trees at Olduvai Gorge. The tree relicts occur in an interval dominated by low-viscosity mass flow and braided fluvial sediments, deposited at the toe of a largely Ngorongoro Volcano-sourced volcaniclastic fan apron that comprised a widely spaced network of ephemeral braided streams draining northward into the Olduvai Basin. Preservation of the trees occurred through their engulfment by mass flows, post-mortem mold formation resulting from differential decay of woody tissues, and subsequent fluvially-related sediment infill, calcite precipitation, and cast formation. Rhizolith preservation was triggered by the interaction of root-induced organic and inorganic processes to form rhizocretionary calcareous root casts. Phytolith analyses were carried out to complete the paleoenvironmental reconstruction. They imply a pronounced seasonality and indicate a wooded landscape with grasses, shrubs, and sedges growing nearby, comparable to the low, open riverine woodland (unit 4c) along the Garusi River and tributaries in the Laetoli area. Among the tree stump cluster were found outsized lithic clasts and those consisting of quartzite were identified as Oldowan stone tool artifacts. In the context of hominin activity, the identification of wooded grassland in association with nearby freshwater drainages and Oldowan artifacts significantly extends our paleoenvironmental purview on the basal parts of Lower Bed I, and highlights the hitherto underrated role of the yet poorly explored western Olduvai Gorge area as a potential ecologically attractive setting and habitat for early hominins.

Early evidence of San material culture represented by organic artifacts from Border Cave, South Africa.

Recent archaeological discoveries have revealed that pigment use, beads, engravings, and sophisticated stone and bone tools were already present in southern Africa 75,000 y ago. Many of these artifacts disappeared by 60,000 y ago, suggesting that modern behavior appeared in the past and was subsequently lost before becoming firmly established. Most archaeologists think that San hunter-gatherer cultural adaptation emerged 20,000 y ago. However, reanalysis of organic artifacts from Border Cave, South Africa, shows that the Early Later Stone Age inhabitants of this cave used notched bones for notational purposes, wooden digging sticks, bone awls, and bone points similar to those used by San as arrowheads. A point is decorated with a spiral groove filled with red ochre, which closely parallels similar marks that San make to identify their arrowheads when hunting. A mixture of beeswax, Euphorbia resin, and possibly egg, wrapped in vegetal fibers, dated to ∼40,000 BP, may have been used for hafting. Ornaments include marine shell beads and ostrich eggshell beads, directly dated to ∼42,000 BP. A digging stick, dated to ∼39,000 BP, is made of Flueggea virosa. A wooden poison applicator, dated to ∼24,000 BP, retains residues with ricinoleic acid, derived from poisonous castor beans. Reappraisal of radiocarbon age estimates through bayesian modeling, and the identification of key elements of San material culture at Border Cave, places the emergence of modern hunter-gatherer adaptation, as we know it, to ∼44,000 y ago.

Environments and hominin activities across the FLK Peninsula during Zinjanthropus times (1.84 Ma), Olduvai Gorge, Tanzania.

We establish through 13 excavations the landscape context and nature of hominin activities across the Zinjanthropus land surface from which the Leakeys recovered the FLK 22 and FLK NN 1 paleoanthropological assemblages. The land surface was created by fluvial incision of the eastern margin of paleo-Lake Olduvai following a major lake withdrawal. Erosion was uneven, leaving a peninsula bounded by a river channel, the FLK Fault, and a freshwater wetland. This FLK Peninsula supported groves of trees that attracted hominins and carnivores, and that preserved the dense concentrations of carcass remains and stone tools they left behind, including those at FLK 22. Some carcasses appear to have been acquired at the ecotone of the Peninsula and Wetland, where another dense artifact and bone assemblage accumulated. A lesser topographic high at the edge of a Typha marsh in the Wetland was the site of FLK NN 1 and a scatter of large stone tools used possibly for rootstock processing. Our landscape reconstruction delimits the vegetation mosaic indicated by previous work and provides a topographical explanation for the existence of FLK 22 and FLK NN 1. Both are unexpected if the FLK area was the flat, featureless lake margin terrain typical of lake basins similar to paleo-Olduvai. The results show that the Leakeys' sites were not isolated occupation floors but rather parts of a land surface utilized intensively by hominins. Although commonly considered to have been home bases, their likely high predation risk, evidenced by large carnivore feeding traces and the remains of four hominin individuals, suggests visits to them were brief and limited to feeding. Finally, stratigraphic observations confirm that FLK NN 3 accumulated on an older land surface, refuting the hypothesis that the OH 8 foot found there is the same individual as the OH 35 leg from FLK 22.

Vegetation during UMBI and deposition of Tuff IF at Olduvai Gorge, Tanzania (ca. 1.8 Ma) based on phytoliths and plant remains.

As part of ongoing research at Olduvai Gorge, Tanzania, to determine the detailed paleoenvironmental setting during Bed I and Bed II times and occupation of the basin by early hominins, we present the results of phytolith analyses of Tuff IF which is the uppermost unit of Bed I. Phytoliths were identified in most of the levels and localities on the eastern paleolake margin, but there are not always sufficient numbers of identifiable morphologies to infer the specific type of vegetation due to dissolution. Some surge surfaces and reworked tuff surfaces were vegetated between successive ash falls, as indicated by root-markings and the presence of a variety of phytolith morphotypes. Dicotyledonous wood/bark types were dominant except at the FLK N site just above Tuff IF when monocots are dominant and for the palm-dominated sample from the reworked channel cutting down into Tuff IF at FLK N. The area between the two fault scarps bounding the HWK Compartment, approximately 1 km wide, was vegetated at various time intervals between some of the surges and during the reworking of the Tuff. By lowermost Bed II times the eastern margin was fully vegetated again. Climate and tectonic activity probably controlled the fluctuating lake levels but locally the paleorelief and drainage were probably the controlling factors for the vegetation changes. These data support a scenario of small groups of hominins making brief visits to the paleolake during uppermost Bed I times, followed by a more desirable vegetative environment during lowermost Bed II times.

Landscape distribution of Oldowan stone artifact assemblages across the fault compartments of the eastern Olduvai Lake Basin during early lowermost Bed II times.

The density and composition of Oldowan stone artifact assemblages deposited during the first ca. 20,000 years of lowermost Bed II times show a recurrent pattern of variation across recognized synsedimentary faults that compartmentalized landscapes of the eastern Olduvai Lake Basin. When active, the faults created minor topographic relief. The upthrown fault footwalls accumulated assemblages with relatively high densities of artifacts, including types retaining potential usefulness, particularly volcanic flaked pieces, manuports, pounded pieces, and split cobbles. Values for these assemblage characteristics decline toward the lower-lying hangingwall of the fault compartments, accompanied by an increase in the proportionate weight of artifact assemblages comprising quartzite, particularly flaking shatter and potentially useful detached pieces. Values reverse once again at faults, either on the downthrown, hangingwall side or on the upthrown side. The patterns are stronger for the volcanic components of the artifact assemblages than for the quartzite components, reflecting the additional influence of distance from the local source on quartzite assemblage characteristics reported previously. The landscape distributions of artifact assemblages are consistent with a landscape-fault model in which minor fault-induced topographic relief at times created a mosaic of vegetation environments repeated within each of the three fault compartments of the lake margin and distal alluvial fan. The fault-compartmentalized landscape model is currently supported only by sediment thickness and facies changes across synsedimentary faults, but it provides predictions for spatial variation in the cover abundance of trees, freshwater reservoirs and associated distributions of resources and hazards associated with stone artifact use and discard that can be tested if sample sizes of key paleoenvironmental indicators are increased.

Fossil sedges, macroplants, and roots from Olduvai Gorge, Tanzania.

A variety of macroplants has been recorded and collected from the eastern paleolake margin of Olduvai Gorge, Tanzania, from Upper Bed I and Lower Bed II, dated at ~1.7-1.85 Ma. The plant groups represented are sedges, grasses, and woody and herbaceous dicotyledons. Most of these plants are fragmented, but the roots are in situ. The modes and quality of preservation, however, are very variable. Silicification is the dominant type of preservation; it ranges from high quality faithful replacement of cells resulting in silicified wood and sedge culms that are identifiable on the basis of their internal anatomy, to poor quality biotubes lacking internal anatomy or external features that prevent assignment to a specific plant or invertebrate origin. In between this range are silicified roots and grass culms identified by their external anatomy, and leaf and stem impressions. Interpretation of the paleoecology is limited by the quality of preservation. The in situ root horizons are useful for recognizing paleo-surfaces. The best quality preservation where internal anatomy is preserved occurs at HWK E and MCK, localities that are in the middle of the fault compartments so the vegetation can be reconstructed for these sites. Some sedge culms are described, illustrated, and identified as possible species of Cyperus, Fuirena, and Schoenoplectus.

Early hominin diet included diverse terrestrial and aquatic animals 1.95 Ma in East Turkana, Kenya.

The manufacture of stone tools and their use to access animal tissues by Pliocene hominins marks the origin of a key adaptation in human evolutionary history. Here we report an in situ archaeological assemblage from the Koobi Fora Formation in northern Kenya that provides a unique combination of faunal remains, some with direct evidence of butchery, and Oldowan artifacts, which are well dated to 1.95 Ma. This site provides the oldest in situ evidence that hominins, predating Homo erectus, enjoyed access to carcasses of terrestrial and aquatic animals that they butchered in a well-watered habitat. It also provides the earliest definitive evidence of the incorporation into the hominin diet of various aquatic animals including turtles, crocodiles, and fish, which are rich sources of specific nutrients needed in human brain growth. The evidence here shows that these critical brain-growth compounds were part of the diets of hominins before the appearance of Homo ergaster/erectus and could have played an important role in the evolution of larger brains in the early history of our lineage.

Taphonomy of the early Miocene flora, Hiwegi Formation, Rusinga Island, Kenya.

A fossil flora was collected in situ from early Miocene deposits at site R117 in the Hiwegi Formation of Rusinga Island contemporaneous with and in close proximity to the sites from where the anthropoid primates were recovered. The flora exhibits a spatially and temporally patchy distribution of fruits and seeds, mixed with twigs of various sizes, fragments of wood, bark, and leaves, all with random orientations and very low depositional dips. There has been minimal transport and the flora evidently accumulated as in situ litter beneath local vegetation. Based on Nearest Living Relatives (NLR) of fruits and seeds, the vegetation represented is a deciduous broad-leaved woodland with continuous canopy, with trees, shrubs, lianas, and climbers, reminiscent of the structure of the modern vegetation in the steep-sided protected valleys in the Laetoli-Endulen area. The interpretation of the vegetation is supported by the presence of twigs, wood, and bark fragments from larger diameter axes. Climbers are represented by twining stem fragments as well as by a wide variety of distinctive fruits and seeds. The proportion of fossilised thorny twigs represents only 3% of the twig collections, and there are no unequivocal forest trees amongst the NLR. No grasses were present; monocotyledons are only represented by a single date palm stone. No conifer seeds or cones have been recovered, and there are no coniferous leafy shoots.