Adrar n Iɣud / ⴰⴷⵔⴰⵔ ⵏ ⵉⵖⵓⴷ | |
 Jean-Jacques Hublin at Jebel Irhoud (Morocco), pointing to the crushed human skull (Irhoud 10), whose orbits are visible just beyond his finger tip | |
  Location in Morocco | |
| Alternative name | جبل إيغود |
|---|---|
| Location | East ofSafi |
| Region | Morocco |
| Coordinates | 31°51′18″N8°52′21″W / 31.85500°N 8.87250°W /31.85500; -8.87250 |
| Height | 592 m |
| History | |
| Periods | Lower Paleolithic |
| Associated with | Homo sapiens |
| Site notes | |
| Excavation dates | 1991 |
Jebel Irhoud orAdrar n Ighoud (Standard Moroccan Tamazight:ⴰⴷⵔⴰⵔ ⵏ ⵉⵖⵓⴷ,romanized: Adrar n Iɣud;Arabic:جبل إيغود,Moroccan Arabic:žbəl iġud), is anarchaeological site located just north of the town ofTlet Ighoud inYoussoufia Province, approximately 50 km (30 mi) south-east of the city ofSafi inMorocco. It is noted for thehomininfossils that have been found there since the discovery of the site in 1961. Originally thought to beNeanderthals, the specimens have since been assigned toHomo sapiens and, as reported in 2017, have been dated to roughly 300,000 years ago (286±32 ka for the Irhoud 3 mandible,315±34 ka based on other fossils and the flint artefacts found nearby).[1][2][3][4]
The site is the remnant of asolutional cave filled with 8 metres (26 ft) of deposits from thePleistocene era, located on the eastern side of akarstic outcrop oflimestone[5] at an elevation of 562 metres (1,844 ft).[6] It was discovered in 1961 when the area was being mined for the mineralbaryte.[7][8] A miner discovered a skull in the wall of the cave, extracted it, and gave it to an engineer, who kept it as a souvenir for a time. Eventually, it was handed over to theUniversity of Rabat, which organized a joint French-Moroccan expedition to the site that was headed by anthropologistÉmile Ennouchi.[9][10]
Ennouchi and his team began their excavation of Jebel Irhoud in 1961. Before beginning excavation, Ennouchi's team removed 2000 tons of debris that covered the archaeological layers using low-level explosives.[11] The excavation completed by Ennouchi's team used horizontal arbitrary 50 cm stratigraphic layers, or spits.[11] Ennouchi's team identified the remains of approximately 30 species of mammals, some of which are associated with theMiddle Pleistocene, but thestratigraphic provenance of these remains is unknown. During the Ennouchi excavations, two hominin fossils, Irhoud 2 and Irhoud 3, were discovered and identified as an adult and a child.[11] The associated lithic technology was identified asMousterian, leading the Irhoud hominins to initially be identified as Neanderthals.[11] Ennouchi's team was also the first to attempt to date the site. They used radiocarbon dating, but their results revealed that the site was older than 50,000 years and was thus beyond the measurement capabilities of radiocarbon dating.[11]
Another excavation was carried out byJacques Tixier andRoger de Bayle des Hermens in 1967 and 1969, during which 22 layers were identified in the cave in search of more hominin fossils.[11] Irhoud 4 and 5 were identified during these excavations and were the first human remains found within a known stratigraphic context at the site,[11] and were found in association with theLevalloisMousterian tool industry.[5]
Jean-Jacque Hublin conducted more recent excavations beginning in 2004.[12] These excavations continued the work of the 1960s excavations, performing a more detailed study of site stratigraphy and context.[12] It was during these excavations that Irhoud 10 and Irhoud 11 were discovered, both of which were identified as adults.[12][13] Recent work identifies the Jebel Irhoud individuals as early members of theH. sapiens clade.[14]
The site's stratigraphic layers were originally defined during the excavations in the late 1980s. Differently defined stratigraphic layers were identified during more recent research, this time using geological principles.[12] A description of the more recent site stratigraphy is as follows: Layers 1-3 do not contain much archaeological material, layers 4-6 contain some archaeological material (lithic tools) and zooarchaeological remains (primarilyGazella species), Layer 7 contains sediment described as "cemented" and contains a higher density of archaeological materials (lithic tools, some burnt) and zooarchaeological remains (primarilybovids) than the upper layers and corresponds to layers where the first Jebel Irhoud fossils were found.[12]
Jebel Irhoud is a site with much geological diversity, including Triassic formations and Charkarkar cave, and Ganntour phosphate deposits. The current geomorphology of Jebel Irhoud was created during an event called theHercynian orogeny.[15] This event occurred between 310 and 280 Ma and created westwardvergent folds.[15] Three primary geological formation contributing the Jebel Irhoud landscape: (1)Barite veins, (2) zones of barite or "substitution," and (3)karst deposits.[15]
Initially, the finds were interpreted asNeanderthal, as thestone tools found with them were believed to be associated exclusively with Neanderthals.
The remains had archaic phenotypical features believed to be representative of the Neanderthals rather thanHomo sapiens. They were thought to be approximately 40,000 years old, but this was thrown into doubt by faunal evidence suggesting a Middle Pleistocene date (see:Faunal Remains and Environmental Context), approximately 160,000 years ago. Because of that, the fossils were reappraised as representing anarchaic form ofHomo sapiens or perhaps a population ofHomo sapiens that had interbred with Neanderthals. This was consistent with the concept thatthe then-oldest-known remains ofHomo sapiens, dated to approximately 195,000 years ago and found inOmo Kibish,Ethiopia, indicated an eastern African origin for humans at approximately 200,000 years ago. The Ethiopian Omo remains were more recently dated to about 233,000 years old.
Dating carried out by theMax Planck Institute for Evolutionary Anthropology inLeipzig revealed that the Jebel Irhoud site was far older than first thought. Fresh excavations carried out in 2004 by the Hublin team revealed more than 20 new bones from the remains of at least five people, and a number of stone tools. The finds included part of a skull, a jawbone, teeth, and limb bones that had come from three adults, a juvenile, and a child aged about seven-and-a-half years old.
Some of the tools had been burned due to fires being lit on top of them, presumably after they had been discarded. Researchers usedthermoluminescence dating to ascertain when the burning of these stone tools occurred and, by proxy, the age of the fossil bones that were found in the same deposit layer.
In 2017, the burnt tools were dated to approximately 315,000 years ago, indicating that the fossils are of approximately the same age. This conclusion was confirmed by recalculating the age of the Irhoud 3 mandible, which produced an age range compatible with that of the tools, at roughly 280,000 to 350,000 years old. If they hold up, these dates would make the remains by far the earliest known examples ofHomo sapiens.[16][17][18]
This suggests that rather than arising inEast Africa approximately 200,000 years ago, modern humans may have been present across the length of Africa 100,000 years earlier. According to study author Jean-Jacques Hublin, "The idea is that earlyHomo sapiens dispersed around the continent and elements of human modernity appeared in different places, and so different parts of Africa contributed to the emergence of what we call modern humans today."[19] Early humans may have comprised a large, interbreeding population dispersed across Africa approximately 330,000 to 300,000 years ago. Thus, the rise of modern humans may have taken place on a continental scale rather than being confined to a particular corner of Africa.[20]
The site is most famous for itshominin fossils, and since its discovery, twenty-two hominin fossil remains have been found at Jebel Irhoud.[11] When first discovered, they were interpreted as Neanderthal remains.[22] Since then, they have also been suggested as being an early form of H. sapiens that interbred with Neanderthals, or they represented a different late-surviving archaic population in Africa.[22] Recent research disputes these claims, concluding that the Jebel Irhoud hominin remains represent an early form of the H. sapiens clade, present during the Middle Pleistocene.[22]
Ennouchi discovered a skull that he named Irhoud 1. It is now on display in theRabat Archaeological Museum. The following year, he discovered part of another skull, designated Irhoud 2, and subsequently uncovered the lowermandible of a child, designated Irhoud 3. Tixier's excavation found ahumerus designated Irhoud 4, and ahip bone recorded as Irhoud 5.
Further excavations were carried out by American researchers during the 1990s and then by a team led byJean-Jacques Hublin starting in 2004.[6][23][16] Hublin and colleagues recently discovered Irhoud 10 and 11, both of which were identified as adults and were integral in determining the species classification of the hominin remains.[22] Hublin and colleagues have also provided the following table of hominin remains found at Jebel Irhoud.[22]
| Specimens | Item ID | Anatomical Part | Year | Stratigraphic Position |
| Irhoud 1 | No ID | Cranium | 1961 | Lower deposits |
| Irhoud 2 | No ID | Cranium | 1962 | Lower deposits |
| Irhoud 3 | No ID | Mandible (juvenile) | 1968 | Lower deposits |
| Irhoud 4 | No ID | Humerus (juvenile) | 1969 | Layer 18 of Tixier |
| Irhoud 5 | No ID | Coxal (juvenile) | 1969 | Layer 18 of de Bayle des Hermens & Tixier |
| Irhoud 6 | No ID | Mandible fragment | 1961-69 | Identified among faunal remains |
| Irhoud 7 | 4766 | Lower right first premolar | 2004 | Initial cleaning |
| Irhoud 8 | 4767 | Distal part of left lower molar | 2004 | Initial cleaning |
| Irhoud 9 | 1653 | First or second lower molar | 2006 | Layer 4 |
| Irhoud 10 | 1678, 1679, 1680, 2178, 2259 | Cranium | 2007 | Layer 7 |
| Irhoud 11 | 4765, 3752 | Mandible | 2007 | Layer 7 |
| Irhoud 12 | 2196 | Lower incisor | 2007 | Layer 7 |
| Irhoud 13 | 2252 | Left proximal femur | 2007 | Layer 7 |
| Irhoud 14 | 2381, 2383 | Rib | 2009 | Layer 7 |
| Irhoud 15 | 2401 | Rib | 2009 | Layer 7 |
| Irhoud 16 | 2561, 2565 | Humerus (juvenile) | 2009 | Layer 7 |
| Irhoud 17 | 2670 | Right proximal femur | 2009 | Layer 7 |
| Irhoud 18 | 2838 | Lumbar vertebra | 2007 | Initial cleaning |
| Irhoud 19 | 3747, 3748, 3749 | Fibula | 2009 | Layer 7 |
| Irhoud 20 | 3751 | Cervical vertebra | 2009 | Initial cleaning |
| Irhoud 21 | 4200 | Maxilla | 2011 | Layer A |
| Irhoud 22 | 4502, 4503 | Upper second and third right molars | 2011 | Layer A |
Hublin and his team also attempted unsuccessfully to obtain DNA samples from the hominin fossils, which would have provided necessary evidence towards the conclusion that these fossils are representative of the main lineage leading up to modern humanity and thatHomo sapiens had dispersed and developed all across Africa. Because of the unclear boundaries between different species of the genusHomo, and the lack of genomic evidence from these fossils, some doubt the classification of these fossils asHomo sapiens.[21]
The most important anatomical considerations when classifying the Jebel Irhoud remains are these specimens' facial/cranial, dental, and mandibular morphologies.[22] Recent studies based on these morphological attributes have identified the Jebel Irhoud individuals as being closer aligned with modern human morphology than archaic hominin morphology, placing them within the early stages of theHomo sapiens clade.[22]
Excavations carried out in 2004 by the Hublin team revealed more than 20 new bones from the remains of at least five individuals and stone tools. The finds included part of a skull, a jawbone, teeth, and limb bones that had come from three adults, a juvenile, and a child aged about seven-and-a-half years old.[25] The facial characteristics of the skull resemble modernH. sapiens but had much larger lower jaws and more elongated posterior braincases. They have similar features to theFlorisbad Skull, which dates to 260,000 years ago, discovered inFlorisbad, South Africa. The Florisbad Skull has now been attributed toHomo sapiens as a result of the Jebel Irhoud finds.[19][26]
Modern and early modern human facial morphology is defined by a short face that sits underneath the braincase.[22] The Jebel Irhoud individuals also had very thickbrow ridges and lackedprognathism, although more recent work has shown that brow ridges among the Jebel Irhoud hominins are variable and may be attributed tosexual dimorphism.[22] Despite some of these facial attributes that might look archaic, statistical analyses have placed the facial shape of the Jebel Irhoud specimens (specifically 1 & 11) as being more closely related to early and recent modern humans.[22] This research was completed using 3D facial reconstructions of fossil specimens.[22]
When comparing the Jebel Irhoud fossils with those of modern humans, the main difference is the elongated shape of thebraincase. According to the researchers, this indicates thatbrain shape, and possibly brain functions, evolved within theHomo sapiens lineage and relatively recently.[16][27][19] Evolutionary changes in brain shape are likely associated withgenetic changes in brain organization, interconnection, and development[28] and may reflect adaptive changes inthe way the brain functions.[29] Such changes may have caused the human brain to become rounder and two regions in the brain's posterior region to enlargeduring thousands of years of evolution.[29]
The dental morphology of the Jebel Irhoud individuals also aligns more closely to early modern humans than to archaic hominins.[22] Although researchers note that their teeth are larger than early modern humans, their third maxillary molar (M3), crown morphology, and molar morphological complexity still place them closer to early modern humans than Neanderthals.[22] The degree of tooth development found in the Jebel Irhoud hominins is similar to that of modern European children of the same age, but teeth roots develop faster than for modern humans (and slower than for apes and some other fossil hominids).Tooth crowns took a longer time to form than in modern humans.[30]
Mandibular morphology refers to the size and shape of themandible or jaw. The most convincing evidence from the study of the Jebel Irhoud specimens' mandibular morphology comes from Irhoud 3. Irhoud 3 has an inverted T-shaped chin, something typically found inHomo sapiens.[22]
While the Jebel Irhoud specimens initially were noted to have been similar to laterAterian andIberomaurusian specimens,[31] further examinations revealed that the Jebel Irhoud specimens differ from them. The Jebel Irhoud specimens have a continuous supraorbital torus, while the Aterian and Iberomaurasian specimens have a discontinuous supraorbital torus or, in some cases, none at all. From this, it was concluded that the Jebel Irhoud specimens represent archaicHomo sapiens while the Aterian and Iberomaurasian specimens represent anatomically modernHomo sapiens. Despite this, it was noted that the Jebel Irhoud specimen, whose cranium was complete enough to assess, showed "hints of 'modern' basicranial flexion in the relationship of the face and vault," and the teeth of another Jebel Irhoud specimen were subjected to synchrotron analysis that suggested "a modern developmental pattern."[32]
The stone tool/lithic assemblage has been associated withMousterian lithic assemblages, but more recently has been described as aMiddle Stone Age assemblage due to the presence of prepared core orLevallois technology and the desire to move towards the usage of an African industry name instead of a European one.[33]
Scrapers are the most common tool type found in the assemblage (specifically Mousterian points and déjeté scrapers), accompanied by cores, piercers, notched pieces, and some flake debris.[34][33] Researchers have noticed that the assemblage contains many retouched tools.[33]Bifacial tools and tools indicative of theAterian industry are also missing from the assemblage.[11][34]
Recent analyses of the lithic assemblages suggest that Trixier's original observations of the lithic assemblages excavated in the 1960s are still consistent in relation to recently excavated assemblages.[34] This assemblage's most common raw materials are flint/chert, quartzite, and quartz. Of these raw materials flint/chert tools are more commonly retouched.[34] The raw material source for the flint tools has been identified as Jebel Khiyyat (Mekala).[11] Jebel Khiyyat is 30 km. south of Jebel Irhoud.[11] The low frequencies of flake debris relative to complete tools and high percentage of retouched tools have caused researchers to suggest that little knapping occurred on-site.[33] The presence of stone tools that have been burned alongside faunal remains and evidence of butchery suggests that the tools were probably used alongside fires at Jebel Irhoud.[34][33]
The faunal assemblage from Jebel Irhoud includes numerous rodents, golden jackal, gazelle (outnumbers all other bovids),Alcelaphine species, leopards, lions, small cats, hyena, and wild boar.[11][35][36][37] Of the faunal remains, only one gazelle bone shows evidence of carnivore chewing (from Layer 6), while most bones in the cave indicate human butchery.[34] Cut marks on small and largebovid ribs, tibia, and humeri occur in layers 4, 6, and 7.[34] The breakage patterns found on these bones are associated with breakage occurring when the animal bones were fresh, i.e., recently killed.[34] Percussion markings on the ends of long bones also hint at potential modification for bone marrow extraction.[34] Also among the faunal assemblages are ostrich egg shells, although more work is needed before assuming that this results from anthropogenic accumulation.[34]
The rodent assemblage was likely accumulated by a carnivore (such as an owl), indicating a Late Middle Pleistocene date for the site. The rodent assemblage, such as the inclusion ofG. grandis andEllobius, also indicates that grasslands probably dominated the surrounding landscape and that during the MiddlePleistocene, the Jebel Irhoud environment was less arid than during the Upper Pleistocene.[35] This is based on the prevalence ofmuris in the mammalian records of the Middle Pleistocene layer recovered during the Ennouchi excavations, and the reduced species diversity found in the Upper Pleistocene.[37] The presence ofmuris in the Middle Pleistocene levels indicates a warmer and more humid climate than an arid one.[37]
In recent years, Jebel Irhoud has been identified as an important place for tourism and cultural heritage, both for its anthropological and geological importance.[15][38] Recently, the Jebel Irhoudgeosite was approved to become a part of the larger Youssoufia geopark project.[15]Proposals to increase tourism to the site have been made with a variety of potential economic and conservational benefits for the area.[15] Additionally, the surrounding area has been highlighted for its potential for barite mining; however, tourism safety concerns have been raised regarding the mining operations.[15] Currently, tourist resources are only available after a while near Jebel Irhoud but are present in nearby towns.[15]
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