The Bouri Formation is an area in the Middle Awash Valley, in Ethiopia

Ethiopia

Ethiopia , officially known as the Federal Democratic Republic of Ethiopia, is a country located in the Horn of Africa. It is the second-most populous nation in Africa, with over 82 million inhabitants, and the tenth-largest by area, occupying 1,100,000 km2...

 that has provided a rich source of Australopithecines and Homo

Homo

Homo may refer to:*the Greek prefix ὅμο-, meaning "the same"*the Latin for man, human being*Homo, the taxonomical genus including modern humans...

 fossils, artifact

Artifact (archaeology)

An artifact or artefact is "something made or given shape by man, such as a tool or a work of art, esp an object of archaeological interest"...

s and bones of large mammal with cut marks from butchery. It is part of the Afar Depression

Afar Depression

The Afar Triangle is a geological depression that is caused by the Afar Triple Junction which is part of the Great Rift Valley. It overlaps Eritrea, Djibouti and the entire Afar Region of Ethiopia. The Afar Triangle includes the Danakil Depression and the lowest point in Africa, Lake Asal...

 that has created other rich human fossil sites such as Gona and Hadar

Hadar

Hadar may refer to:* Beta Centauri, a star* Hadar, Ethiopia* Hadar, Haifa, a quarter of Haifa, Israel* Hadar, Nebraska* Hadar, a village in the Syrian Golan.People:* Hadad , several biblical characters, also known as Hadar...

.

It consists of three geological units called members in which fossils and artifacts from different periods of human evolution has been excavated. The lowest Hatayae member (2.5 mya) in which Australopithecus garhi

Australopithecus garhi

Australopithecus garhi is a gracile australopithecine species whose fossils were discovered in 1996 by a research team led by Ethiopian paleontologist Berhane Asfaw and Tim White, an American paleontologist. The hominin remains are believed to be a human ancestor species and the final missing link...

 fossils have been found, the Dakanihylo member (1 mya) and Homo erectus

Homo erectus

Homo erectus is an extinct species of hominid that lived from the end of the Pliocene epoch to the later Pleistocene, about . The species originated in Africa and spread as far as India, China and Java. There is still disagreement on the subject of the classification, ancestry, and progeny of H...

, and the Herto member lower (260 ka) and upper layers (160 to 154 ka) and Homo sapiens idaltu

Homo sapiens idaltu

Homo sapiens idaltu is an extinct subspecies of Homo sapiens that lived almost 160,000 years ago in Pleistocene Africa. is from the Saho-Afar word meaning "elder or first born"....

.

Human remains from the Upper Herto layers have been found with signs of having been changed after death by mortuary practices.

Geology

The Bouri Formation occurs in the Bouri “peninsula”, a geological fault raised horst  that diverts the Awash River

Awash River

The Awash is a major river of Ethiopia. Its course is entirely contained within the boundaries of Ethiopia, and empties into a chain of interconnected lakes that begin with Lake Gargori and end with Lake Abbe on the border with Djibouti, some 100 kilometers from the head of the Gulf of Tadjoura...

 and forms a partial dam creating Lake Yardi. The peninsula is about 4 km wide and 10 km in length and lies in a NNW-SSE direction in the Quaternary

Quaternary

The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...

 period rift zone

Rift zone

A rift zone is a feature of some volcanoes, especially the shield volcanoes of Hawaii, in which a linear series of fissures in the volcanic edifice allows lava to be erupted from the volcano's flank instead of from its summit...

 of the southern Afar Region

Afar Region

Afar is one of the nine ethnic divisions of Ethiopia, and is the homeland of the Afar people. Formerly known as Region 2, its current capital is Asayita; a new capital named Semera on the paved Awash - Asseb highway is under construction....

.

The Bouri peninsula contains the Bouri formation, a sediment

Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

 area that stretches down much of its length and breath and is 80 m thick. It is eroded to expose three geological members or layers: the Hatayae (also known as Hata), the Dakanihylo (also known as Daka) and the Herto.

The area is of importance since active tectonics in the southern Afar Depression in the last few million years have created varied types of habitats for early hominids during the Plio-Pleistocene

Plio-Pleistocene

The term Plio-Pleistocene refers to the geological period more recent than circa 5 million years ago, incorporating both the formally defined epochs of the Pliocene and the Pleistocene...

. Then more recently these habitats laid down in sedimentary rocks have been uplifted

Tectonic uplift

Tectonic uplift is a geological process most often caused by plate tectonics which increases elevation. The opposite of uplift is subsidence, which results in a decrease in elevation. Uplift may be orogenic or isostatic.-Orogenic uplift:...

 allowing their erosion

Erosion

Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

 and so accessibility to paleoanthropologist

Paleoanthropology

Paleoanthropology, which combines the disciplines of paleontology and physical anthropology, is the study of ancient humans as found in fossil hominid evidence such as petrifacted bones and footprints.-19th century:...

s. Occasional volcanic eruptions have also left volcanic tuff

Tuff

Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...

 layers that allow the sedimentary deposits to be accurately argon–argon isotope dated.

Hatayae

The Hatayae layer as its base is 40 m thick made up of variegated silt

Silt

Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...

 clay and paleosol

Paleosol

In the geosciences, paleosol can have two meanings. The first meaning, common in geology and paleontology, refers to a former soil preserved by burial underneath either sediments or volcanic deposits , which in the case of older deposits have lithified into rock...

s, zeolitic and bentonitic tuffs, carbonate

Carbonate rock

Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite and dolostone, which is composed of the mineral dolomite .Calcite can be either dissolved by groundwater or precipitated by...

s that are pedogenic

Pedogenesis

Pedogenesis is the science and study of the processes that lead to the formation of soil ' and first explored by the Russian geologist Vasily Dokuchaev , the so called grandfather of soil science, who determined that soil formed over time as a consequence of...

, sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

 with bivalve and gastropod shells, and mudstone

Mudstone

Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...

. It was deposited in a floodplain

Floodplain

A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...

  along river delta

River delta

A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...

 channels and a shallow fluctuating lake

Lake

A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

 dated to around 2.5 mya.

In the Hatayae Member have been found the remains of Australopithecus garhi

Australopithecus garhi

Australopithecus garhi is a gracile australopithecine species whose fossils were discovered in 1996 by a research team led by Ethiopian paleontologist Berhane Asfaw and Tim White, an American paleontologist. The hominin remains are believed to be a human ancestor species and the final missing link...

. These are most complete for the specimen, BOU-VP-12/130. This species is “descended from Australopithecus afarensis and is a candidate ancestor for early Homo.”

Excavations have in general failed to find large numbers of stone tool

Stone tool

A stone tool is, in the most general sense, any tool made either partially or entirely out of stone. Although stone tool-dependent societies and cultures still exist today, most stone tools are associated with prehistoric, particularly Stone Age cultures that have become extinct...

s. The explanation for this is the lack of raw materials for making them on lake margins. This would have been due to the lack of streams strong enough to carry pebbles, and the absence of nearby basalt outcrop

Outcrop

An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. -Features:Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be...

s.”

However, in spite of rarity some isolated and widely scattered cores and flakes have been found of Mode I technology. As the excavators note “our surveys and excavations have demonstrated that early hominids were actively using stone tools on the PlioceneHata landscape.” Moreover that “It is not currently possible to positively identify the creators of the earliest stone tools here or at Gona, even though A. garhi is currently the only recognized hominid taxon recovered from Hata sediments.”

Evidence of the existence of stone tools is also provided by bones of large mammals of such as alcelaphinae

Alcelaphinae

The subfamily Alcelaphinae contains Wildebeest, Hartebeest, Bonteboks and several similar species. All in all it contains 10 species in 4 genera, although Beatragus is sometimes considered a subgenus of Damaliscus, and Sigmoceros for the Lichtenstein's Hartebeest.* Family Bovidae** Subfamily...

 (Wildebeest related bovid

Bovid

A bovid is any of almost 140 species of cloven-hoofed ruminant mammal at least the males of which bear characteristic unbranching horns covered in a permanent sheath of keratin....

s) and Hipparion

Hipparion

Hipparion is an extinct genus of horse living in North America, Asia, Europe, and Africa during the Miocene through Pleistocene ~23 Mya—781,000 years ago, existing for...

 (an extinct genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of three-toed horse) by hominids showing butchery cut marks including those used to remove an animal’s tongue. “These are the earliest documented percussion marks made by hominids who were presumably processing these bones for contained fatty marrow. …These are the earliest documented cut marks made by hominids.” As noted by its excavators, the evidence from the site shows that “a major function of the earliest known tools was meat and marrow processing of large carcasses. Finally, they extend this pattern of butchery by hominids well into the Pliocene.”

Dakanihylo

The Dakanihylo layer is 22 to 45 m thick and made up of pumice

Pumice

Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...

 sandstone that is cross-bedded

Cross-bedding

In geology, the sedimentary structures known as cross-bedding refer to horizontal units that are internally composed of inclined layers. This is a case in geology in which the original depositional layering is tilted, and the tilting is not a result of post-depositional deformation...

. It is dated to 1 mya and found in the southern half of the Bouri horst. Fossils suggest open grassland (377 species of bovid

Bovid

A bovid is any of almost 140 species of cloven-hoofed ruminant mammal at least the males of which bear characteristic unbranching horns covered in a permanent sheath of keratin....

s including three new species and two new genera, and water-margin habitats (species of Kobus antelope

Kobus (antelope)

Kobus is a genus containing 6 species of African antelopes, all of which are associated with marshes, floodplains or other grassy areas near water...

 and abundant Hippopotamus

Hippopotamus

The hippopotamus , or hippo, from the ancient Greek for "river horse" , is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae After the elephant and rhinoceros, the hippopotamus is the third largest land mammal and the heaviest...

).

In the Dakanihylo Member has been found early Acheulean

Acheulean

Acheulean is the name given to an archaeological industry of stone tool manufacture associated with early humans during the Lower Palaeolithic era across Africa and much of West Asia, South Asia and Europe. Acheulean tools are typically found with Homo erectus remains...

 stone tools such as hand axe

Hand axe

A hand axe is a bifacial Stone tool typical of the lower and middle Palaeolithic , and is the longest-used tool of human history.-Distribution:...

s and cleaver

Cleaver (tool)

In archaeology, a cleaver is a name given to a type of biface stone tool of the Lower Palaeolithic.Cleavers are a little like hand axes. They are large and oblong or U-shaped tools meant to be held in the hand, but unlike hand axes, they have a wide, straight cutting edge running at right angles...

s and evidence of butchery upon equids, bovid and hippo bones.

Homo erectus

Homo erectus

Homo erectus is an extinct species of hominid that lived from the end of the Pliocene epoch to the later Pleistocene, about . The species originated in Africa and spread as far as India, China and Java. There is still disagreement on the subject of the classification, ancestry, and progeny of H...

 fossils include specimen BOU-VP-2/66 of an incomplete skull

Calvaria (skull)

The calvaria is the upper part of the cranium and surrounds the cranial cavity containing the brain.The calvaria is made up of the frontal, occipital and right and left parietals....

 that had an endocranial capacity of 995 cm³. These fossils of H. erectus are important since it has been suggested that Asian and African H, erectus were different human species

Human taxonomy

Human taxonomy is the classification of the species Homo sapiens , or modern human. Homo is the human genus, which also includes Neanderthals and many other extinct species of hominid; H. sapiens is the only surviving species of the genus Homo. Extinct Homo species are known as archaic humans...

. But these fossils do not support “the hypothesis of a deep cladogenesis between African and Asian H. erectus” and that “that geographic subdivision of early H. erectus into separate species lineages is biologically misleading, artificially inflating early Pleistocene species diversity.” Moreover, they suggest that the H. erectus taxon had “by 1 Myr the taxon had colonized much of the Old World without speciating. A finding of
considerable biogeographic and behavioural significance”.

Herto

The Herto layer is named after a local village and consists of a 15–20 m thick layer. It is found in the southwestern part of the Bouri horst and consists of a lower and an upper layer. The division between the Lower and Upper Herto layers is characterized by an erosion surface filled with rounded pebbles.

Lower Herto

This consists of lignite

Lignite

Lignite, often referred to as brown coal, or Rosebud coal by Northern Pacific Railroad,is a soft brown fuel with characteristics that put it somewhere between coal and peat...

, pinkish carbonate layers, and silty clays of predominantly lake origin containing gastropods and bivalves. It is dated to 260 ka. Late Acheulean

Acheulean

Acheulean is the name given to an archaeological industry of stone tool manufacture associated with early humans during the Lower Palaeolithic era across Africa and much of West Asia, South Asia and Europe. Acheulean tools are typically found with Homo erectus remains...

 tools are found together with “hominid remains that are as yet unknown”. Humans in this habitat lived next to a freshwater lake and killed large mammals such as hippopotamids.

Upper Herto

The Upper Herto Member changes from the fluvial

Fluvial

Fluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them...

 and lake-margin deposits of the lower layer to yellow sandstone and date to between 160 ka and 154 ka BP. Immediately above the erosion surface separating the two layers is volcanic sandstone and gravel

Gravel

Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...

 deposits that have variable thickness. It is a yellow-brown to grey colour and shows cross-bedded sedimentation containing pumice rocks up to 15 cm in diameter. This layer has produced all the human fossils and tools found in the Upper layer. The Upper layer is topped by a volcanic tuff. An important feature is that two volcanic layers of very fine ash occur one just below the hominid fossils and one just above and this allows an accurate date by argon–argon dating to between 160,000 and 154,000 years ago to be given to adjacent sediment layers and their fossils. This is significant “because the accurate dating of faunas and artefacts of many sites of this general antiquity in Pleistocene Africa has proved notoriously difficult.”

In this layer have been found early Middle Stone Age

Middle Stone Age

The Middle Stone Age was a period of African Prehistory between Early Stone Age and Late Stone Age. It is generally considered to have begun around 280,000 years ago and ended around 50-25,000 years ago. The beginnings of particular MSA stone tools have their origins as far back as 550-500,000...

 tools and the remains of Homo sapiens idaltu

Homo sapiens idaltu

Homo sapiens idaltu is an extinct subspecies of Homo sapiens that lived almost 160,000 years ago in Pleistocene Africa. is from the Saho-Afar word meaning "elder or first born"....

. Most of the tools are scraper

Scraper (archaeology)

In archaeology, scrapers are unifacial tools that were used either for hideworking or woodworking purposes. Whereas this term is often used for any unifacially flaked stone tool that defies classification, most lithic analysts maintain that the only true scrapers are defined on the base of...

s, cleavers, and various lithic core

Lithic core

In archaeology, a lithic core is a distinctive artifact that results from the practice of lithic reduction. In this sense, a core is the scarred nucleus resulting from the detachment of one or more flakes from a lump of source material or tool stone, usually by using a hard hammer percussor such...

s. Hand axes, picks and blade

Blade (archaeology)

In archaeology a blade is a type of stone tool created by striking a long narrow flake from a stone core.Blades are defined as being flakes that are at least twice as long as they are wide and that have parallel or subparallel sides and at least two ridges on the dorsal side...

s are rare. Most stone tools are made of fine-grained basalt

Basalt

Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...

, except for points and blades that were made from obsidian

Obsidian

Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock.It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth...

. Many are made with the Levallois technique

Levallois technique

The Levallois technique is a name given by archaeologists to a distinctive type of stone knapping developed by precursors to modern humans during the Palaeolithic period....

. They are comparable to those found in the Garba III layer at Melka Kunture

Melka Kunture

Melka Kunture is a Palaeolithic site in Ethiopia. It is located 50 kilometers south of Addis Ababa by road, across the Awash River from the village of Melka Awash, with a latitude and longitude of...

.

As at Herto, Garba III includes terminal Acheulean hand axes, typical Levalloisian method, and many retouched tools on flakes (side-scrapers and end-scrapers, backed knives, burins, unifacial and bifacial points). The Garba III assemblage has been considered transitional between the Acheulean and the MSA.

In this layer are found a large number of Hippopotamus bones: “One occurrence shows abundant remains of several hippo calves, mostly newborn to a few weeks old, scattered together with butchered adults.”.

Mortuary practices

Of 15 of the 24 recovered fragments of humans in the Upper Herto layer have cut marks due to soft tissue

Soft tissue

In anatomy, the term soft tissue refers to tissues that connect, support, or surround other structures and organs of the body, not being bone. Soft tissue includes tendons, ligaments, fascia, skin, fibrous tissues, fat, and synovial membranes , and muscles, nerves and blood vessels .It is sometimes...

 removal. It has been noted that “The latter pattern of bone surface modification is almost never present in hominid or nonhuman faunal remains processed for consumption, and is therefore unlikely to represent evidence of utilitarian or economic behaviour.” On one skull, “this defleshing manipulation must have occurred after removal of the mandible. The intentional and deliberate removal of soft tissues such as basicranial vessels, nerves and muscles is therefore indicated. The specimen lacks the entire occipital region surrounding the foramen magnum, and the edges of this broken region are smooth and polished, as are the specimen’s unweathered parietal surfaces.”

Ethnographic study upon modern cultures suggests that such post-mortem manipulation could be due to “curation of human remains as part of mortuary practices”.