Homo antecessor

The Homo antecessor is an extinct species belonging to the genus Homo, whose fossil remains were discovered in 1994 in the Sierra de Atapuerca, in Spain, and which have been dated to about 800,000 years, corresponding to the Calabriense period during the Early Pleistocene.

His name comes from the Latin: Homo – "man"; antecessor – “explorer”, “pioneer” or “early settler”, because it was considered the oldest hominid species in Europe. Fossil or lithic remains have been found in European sites dating from 1 to 1.6 million years, but none of them have sufficient fossil remains to be able to attribute them to a precise human species, so Homo antecessor continues to appear as the oldest species in western and central Europe..

They were tall (at least 160 cm tall), strong, broad-chested and rather heavy individuals with unique facial morphology, including facial bones of “modern” features, but “primitive” crowns and teeth roots. ”, and with a brain smaller than that of HSAMs (Homo Anatomically Modern Sapiens). Its limbs were long, with slender kneecaps and feet indicating that H. antecessor walked and transmitted body weight differently than modern humans.

The H. antecessor made pebbles and simple flakes of quartz and flint among other materials. This Mode 1 lithic industry may represent a precursor to the Acheulean industry, which later spread into Western Europe and Africa. We have no evidence of the use of fire, so they must have inhabited the interior of Iberia in warm periods and on the coast in cold periods.

There is intense scientific debate regarding the taxonomic classification of H. antecessor and its relationships with other species of the genus Homo, since the known specimens represent juvenile stages and a complete adult skull is missing. The increase in the fossil record in Europe and Africa, and new methods have led to different interpretations of its hypothesized phylogenetic position and possible evolutionary scenarios.

In 1997, the Atapuerca research group, with the support of other paleoanthropologists, considered the discovered hominin remains to be a new species, H. antecessor, suggesting that it was an evolutionary link between H. ergaster and H. heidelbergensis, and therefore would be a probable ancestor of the line H. heidelbergensis – H. neanderthalensis, being in turn the last common ancestor (UAC) between modern humans and neanderthals. H. antecessor has a unique mosaic of primitive features of the Homo clade, some derived features present in modern humans, some derived features shared with H. neanderthalensis and their ancestors in the European Middle Pleistocene, and others with Middle Pleistocene Asian hominins. A speciation could have occurred in West Africa/Eurasia, giving rise to a new clade Homo. The H. antecessor could be a side branch of this clade that will give rise to the UAC later, located in the westernmost region of the Eurasian continent.

On the other hand, some scientists believe that the remains of H. antecessor belong to individuals of H. heidelbergensis, which inhabited Europe between 600,000 and 250,000 years ago in the Middle Pleistocene. Finally, other scientists consider them to be a variety of Homo erectus / Homo ergaster.

Another question that remains to be answered is how these hominins arrived in Europe. Hominids from Sima del Elefante in Atapuerca are different from H. erectus, but show similarities to specimens found in Asia. They could come from a migration of those from Africa 1.9 Ma ago, which would have traveled through Europe through the Levantine Corridor, while their organisms adapted to environmental conditions until they constituted a differentiated demo that would give rise to H. antecessor. The other hypothesis is a crossing from Africa to Europe through the Strait of Gibraltar and the Alboran Sea.

History of the excavations

It had long been known that the Sierra de Atapuerca, in northern Spain, 14 km from Burgos, abounded in fossil remains. It is a karstic landscape where many caves were formed, which filled up during the Pleistocene. The discovery of the archaeological potential of this Sierra occurred at the beginning of the 20th century during the construction of a mining railway line, which was never completed.

Map of Atapuerca sites

The first exploration was done in 1966 by the Spanish prehistorian Francisco Jordá Cerdá who found some animal fossils and stone tools, but due to lack of resources he had to abandon the exploration. In 1976, the Spanish paleontologist Trinidad Torres investigated the Gran Dolina in search of bear fossils, recovering some Ursus, but the Edelweiss Speleological Group advised him to continue to the nearby Sima de los Huesos, where he found bear fossils and archaic human fossils. This triggered a massive exploration of the Sierra de Atapuerca, whose director was the Spanish paleontologist Dr. Emiliano Aguirre, and later by the current directors Dr. José María Bermúdez de Castro, Dr. Eudald Carbonell and Dr. Juan Luis Arsuaga. Atapuerca proved to be the world's most important deposit of fossils from the Middle Pleistocene, initially dated between 780,000 and 125,000 years ago. Only in the Sima de los Huesos in 1993 more than 1300 fossils attributable to the genus Homo were recovered.

In 1990, at the Sima de los Huesos site, the Atapuerca team discovered stone tools dating back almost a million years, which contradicted the assumption at the time that the genus Homo had populated Europe only 500,000 years ago.

Excavation of the Gran Dolina was resumed in 1992, and on July 8, 1994 archaic human remains were found at level TD6, which successive datings have consolidated with an age of 780,000 to 850,000 years, which meant advance European colonization by 300,000 years compared to what was assumed at the time (it would later be known that this colonization was greater than a million years). Initially, these fossils were published as an ancient population of H. heidelbergensis from the Middle Pleistocene, from an evolutionary lineage that would give rise to the classical Neanderthals.

In the 1995 campaign, Dr. Aurora Martín Nájera discovered the maxilla of an immature 10 or 11-year-old individual (ATD6-69), who was called “the boy from the Gran Dolina” (later it would be known that corresponded to a girl), studied by Dr. Arsuaga and his collaborators in 1997, and with a face similar to Homo sapiens (coronal orientation of the infraorbital surface and canine fossa type H. sapiens , nose projected forward,...). of the Science magazine, a new species of the genus Homo, the H. antecessor and the hypothesis that it was the common ancestor of H. sapiens and H. neanderthalensis. The reception was cold by the scientific community, since the first fossil DNA data placed the divergence between the two species at 400,000 years. The holotype of the new species was the ATD6-5 specimen, a fragment of the right mandibular body that conserves molars and some isolated teeth.

In 2003 new fossil remains H. antecessor that provided a lot of information, and identified characters linked to H. sapiens or shared with the H. neanderthalensis and their Middle Pleistocene ancestors. The idea that H. antecessor is related to the origin of our species and of the Neanderthal, while geneticists pushed the UAC limit back to 765,000 years.

Potential sites related to H. antecessor

Excavation of the Grand Dolina deposit in Atapuerca (Burgos). The TD6 level is the one that is digging under the scaffolding.

Most of the remains of H. antecessor have been found at the Gran Dolina site in the Sierra de Atapuerca (Spain). Other potential sites related to this species, although some raise serious doubts as we will see later, are the Sima del Elefante in the same Sierra de Atapuerca, the Ceprano site (Italy), and the Happisburgh site in Norfolk (England).

Gran Dolina site, Atapuerca, Spain

Located in the Sierra de Atapuerca Railway Trench (Burgos, Spain), the Gran Dolina site is made up of Pleistocene sediments accumulated in a large ancient cave, which over time was filled with clay, sand, gravel and limestone blocks. Its geological column covers 25 meters, divided into 11 stratigraphic units, from the oldest TD-1 at the bottom, to the most modern TD-11 at the top.

In 1993 an initial excavation (vertical excavation) of 6 m² was carried out, where the first bone remains associated with the genus Homo appeared in stratum TD6, which which warranted further investigation. The first remains (bone fragments and teeth attributable to the genus Homo) of H. antecessor were recovered in the TD6-2 layer in July 1994, a layer that received the nickname of Aurora after its discoverer, the archaeologist Aurora Martín Nájera. The TD6 level is 2.5 meters thick and consists of a clayey matrix cast. The TD6-2 layer is 20 to 30 cm thick and is made up of finer clay materials, the product of calm sedimentation.

In the 1994 and 1995 campaigns, 86 human remains of at least six individuals and 150 mode 1 artifacts were recovered in the Aurora stratum and the TD6 level. The study of human fossils showed a unique combination of primitive and derived traits with respect to the Homo clade, which led to the proposal in 1997 of a new species, H. predecessor. In the campaigns from 2003 to 2007, a triangular section of 13 m² was excavated, where another 80 human remains were recovered, the TD6 stratigraphic sequence was refined and additional geochronological information was found, which allowed us to formulate hypotheses. information on the origin of H. antecessor which we will see later.

Estratigraphic Section Gran Dolina Foundation in Atapuerca

A total of 170 fossils of H. antecessor of about 9 individuals, almost all under 15 years of age, and many under 2 years of age. These remains were first thought to come from the Aurora stratum alone, but are now thought to come from 2 or 3 strata. It should be noted that certain bones show cut marks and percussion spikes, similar to those of other faunal remains, indicating that these humans were processed to obtain meat through a similar slaughter process. In addition, some 200 stone tools, including a stone-carved knife, and some 300 animal bones have also been found. The lithic remains correspond to the Olduvayense tradition and were used for butchering and woodworking. TD6 faunal remains include large herbivores, carnivores, birds, small mammals, small amphibians, and reptiles.

Based on faunal findings, including various rodent species, the shape of stone tools, and paleomagnetic measurements, fossils from the TD6 layer were initially estimated to be at least 780,000 years old. The fossils have been dated in 2018 between 772 and 949 ka BP.

Sima del Elefante, Atapuerca, Spain

The Sima del Elefante site is located in the Sierra de Atapuerca, about 200 meters from the Gran Dolina site. In 2007, the team led by Eudald Carbonell discovered an isolated molar and a small jaw fragment including 7 teeth there, in unit TE-9c (Elephant Trench). Later, in 2008, they found a phalanx of an auricular or little finger. Mandible ATE9-1 was provisionally assigned to H. antecessor, as belonging to a 20-year-old individual. In addition, 32 Olduvayense or Mode 1 flint tools were found, as well as bones of sacrificed animals.

ATE9-1

The most accurate dating method used was Al and Be radioisotope dating on quartz samples. A sample at the TE9b level, 40 cm above the TE9c level mandible, gave an age of 1.22 Ma. Therefore, this would be the minimum age for remains from the TE9c and lower levels. If the dating is correct, it would be one of the oldest hominin finds in Europe.

Human activity in Europe dates back as far as 1.6 Ma in Eastern Europe and Spain based on stone tools found, but in 2013 a 1.4 Ma infant tooth was discovered in Barranco León, Orce, Spain, which would be the oldest known human fossil in Europe.

Detailed study of the ATE9-1 mandible, which presents dentition and symphysis characteristics that approximate it to the oldest Homos from Africa and Dmanisi (Georgia) but with some derived character (internal part of the symphysis), have subsequently led, in 2011, to identify these remains as Homo sp. (genus Homo but without specifying the species), since they probably belong to a new species yet to be defined, and whose phylogenetic relationships, without further data, are still imprecise.

Therefore, based on the remains found so far, the H. antecessor did not inhabit this cave.

Ceprano deposit, Italy

The fossil of the calvaria (upper part of the skull) of Ceprano (Italy) was found on March 13, 1994 in an emergency excavation, when building a highway in the Campogrande region, about 100 km from Rome. The neurocranium could be reconstructed with the recovered fragments, but the facial bones could not be located. The cranial remains were in a highly hardened layer of clay, with no other fossil or pollen remains. The study of regional stratigraphic correlations suggests an age between 350 and 1,000 ka. The Italian paleontologists Antonio Ascenzi (1996) and Giorgio Manzi (2004) believe that it corresponds to 800 or 900 ka ago, which would be consistent with the fauna found from the Lower Pleistocene and lithic industries of Mode 1.

Holotype of the Homo cepranensis.

Ceprano's skull was described by Ascenzi in 1996 as a combination of features from H. erectus and others (e.g. development of frontal sinuses), and with a cranial capacity of 1200 cc, that is, a greater encephalization compared to H. erectus. In 2003 the species Homo cepranensis was proposed, but the phylogenetic, chronological, archaeological and geographical characteristics of the remains found have led some authors to attribute them to Homo antecessor after a study on the presence or absence of certain cranial characters in 20 specimens from the Lower and Middle Pleistocene. From a morphological point of view, Ceprano's calvaria occupies an intermediate position between H. ergaster and H. erectus, and European and African specimens from the Middle Pleistocene.

The fossils of Ceprano and Atapuerca cannot be directly compared because they belong to different anatomical parts and to individuals of different ages, but both sets present intermediate features between the primitive Homo populations of Africa and those of Homo heidelbergensis from Europe. In addition, the absolute dating and the lithic industry of Ceprano are consistent with those of level TD6 of the Gran Dolina.

However, it is necessary to highlight certain magnetostratigraphic analyzes carried out in 2009 of lake and fluvial sediments in the area of discovery, which show an age of 0.5 to 0.35 Ma for this stratigraphic level, which if confirmed could impact the positioning of Ceprano's Homo in the phylogenetic line of the genus Homo (Muttoni, 2009), and would indicate that it would not belong to H. predecessor.

Happisburgh's prints, with a lens cover of a camera as a scale reference.

Norfolk site, England

In 2010 it was reported the discovery of tools at the town of Happisburgh, Norfolk, in eastern England, dating to 780,000 years BP.

In 2014, Chris Stringer's team discovered 50 fossil footprints dating from 1.2 to 0.8 Ma in the muddy sediments of an estuary on Happisburgh beach, corresponding to five individuals, one adult and several juveniles, in the same geological formation in which the previous remains appeared. Using these footprints, the height has been estimated between 0.93 and 1.73 m. The footprints, dated between 1.0 and 0.78 Ma (a period when the island was attached to the mainland), are tentatively attributed to Homo antecessor due to the similar age of the Atapuerca remains..

Anatomy of Homo antecessor

The human fossils of TD6b obtained so far correspond to cranial and postcranial remains, teeth, jaw and face, as well as remains of feet and hands, some of them in a good state of conservation and others in which signs have been detected of cannibalism. It has been possible to estimate the MNI (Minimum Number of Individuals) at 9, in hypodigma TD6 (in all its fossil material), despite the fragmentation of some hominin remains, highlighting the notable presence of a high percentage of immature individuals.

Skull

Among the cranial remains recovered from TD-6 in Gran Dolina, the following stand out:

• ATD6-15 partial remains of the face of a child aged 10 to 11.5 years. It preserves the right torus and part of the region of the glabela. Very developed front breasts. The cranial capacity could be 1000 cc.
• ATD6-19 small adult cigomaxilar fragment, with cigomaxile tuber as ATD6-58, projected outward 2 mm (Arsuaga 1999).
• ATD6-58 left cigomaxilar fragment of an adult. Notable canine pit and large cigomaxilar tube in maxillary position projected out 3.3 mm (Arsuaga 1999).
• ATD6-100/168 the greatest fragment of parietal recovered. Morphology fractures compatible with peri-mortem trauma. Flat upper pacifiers. Great parietal and small foramen accessory. Slim bone, probably of a young man (Bruner 2016).

Reconstruction of the Homo ancessor skull from a reproduction of the found fragments (Museum of Archaeology of Catalonia in Barcelona).

From the reconstruction of the skull of H. antecessor based on the reproduction of the fragments found, a cranial capacity is estimated in H. antecessor of about 1,000 cc, that is, a lower degree of encephalization than Homo sapiens (1,350 cc). The brain is lateralized.

The parietal bones are flattened and join in a peak in the midline, a profile called tent that is also found in H. ergaster more archaic African and in the H. erectus asiatic. Like the H. ergaster, the styloid process, just below the ear canal, is fused to the base of the skull. The brow ridges are prominent. The upper margin of the squamous part of the skull-side temporal bones is convex, as in more derived species.

Regarding the characteristics of the skull, TD6 hominins share with Neanderthals and present-day humans a convex upper edge of the temporal scale, as well as an anterior position of the incisor canal that is almost vertical. In contrast, the double-arched supraorbital torus is clearly distinguishable from H. erectus.

Jaw and dentition

Among the fossils related to the jaw and dentition in Gran Dolina, the following stand out:

• ATD6-5, hemimandible with three molars of a young individual. It can be observed that the eruption of the third molar M3 is irregular, which implies that the individual suffered toothache and/or inability to bite. It does not have preneandertal traits or similar to H. ergaster.
• ATD6-38, size and shape similar to ATD6-69. Topography suggests the presence of a canine pit (Arsuaga, 1999).
• ATD6-69 represents the so-called Big Dolina boy (H3). It corresponds with much left side face, except for the frontal apophysis of the zygomatic and maxillary bones. Dental age: 10-11 years. Morphology and pattern dental development, modern (BdC 1999) with features closer to skulls of Zhoukoudian, Dali and Cromagnon than to neandertal. It has recently been determined that it corresponds to a female individual.
• ATD6-92 masculine individual tooth fragment, which was used to perform the first ESR dating H. predecessor and get the oldest human proteoma so far.
• ATD6-93 M1 lower right with the largest bucolingual diameter found so far in the genus Homo.
• ATD6-96 left fragment of the jaw of a very young woman. Hypertrophied pterigoid tube, apomorphic characteristic neandertal.

In general, the lower jaw is more gracile than that of other archaic humans, although it shows some archaic features, but the shape of the mandibular notch is similar to that of modern humans, and the alveolar part (adjacent to the teeth) is completely vertical as in modern humans. Like many Neanderthals, the medial pterygoid tubercle is large. Unlike most Neanderthals, there is no retromolar space between the last molar and the end of the mandible.

The upper incisors are spade-shaped (the lingual side is concave), a characteristic feature of other Eurasian humans, including modern ones. The canines have a cingulum (bump toward the base) and essential ridge (toward the midline) as derived characters, but retain the cuspula (small bumps) near the edge of the incisor as more archaic characters. The crowns of the upper premolars are derived, almost symmetrical, and with a lingual cusp (on the side of the tooth in contact with the tongue), and a cingulum and longitudinal grooves in the buccal region (on the side in contact with the buccal tissue).. The upper molars show certain features of Neanderthals. The mandibular teeth are quite archaic. P3 (mandibular first premolar) has an asymmetric crown and is smaller than P4, like other primitive Homo. M1 (mandibular first molar) is smaller than M2 and the cusps of the molar crowns are Y-shaped. The distribution of dental enamel is Neanderthal type, thicker at the periphery than at the cusps..

The dental sample of H. antecessor (ATD6-69 and ATD6-13) has been used to assess the variability of dental tissue in permanent canines (from 6 years of age onwards). Microtomographic techniques have been used to measure the volumes of the crown and the surface areas of its enamel layers and dentin-pulp complexes of H. antecessor, and compare the results with data obtained from hominins from Sima de los Huesos (16 samples) in Atapuerca, Krapina (12 samples) in Croatia, and other known sites (58 samples). The results show significant variability between the canines of individuals H1 (dental pieces: ATD6-1, ATD6-6 and ATD6-13) and H3 (ATD6-69), which could be interpreted as a sign of sexual dimorphism, since women have smaller teeth, relatively thicker enamel, and a lower proportion of gum coverage. H1 could be a male individual and H3 a female individual (92.3% reliability rate). Future discoveries may support or refute this hypothesis.

"Homo antecessor" in Gran Dolina (ATD6-15 and ATD6-69).

A study using computerized microtomography on the trigonid crests of the molars has compared 274 molars from the TD6 level (14 samples) and from Pleistocene African, European and Asian hominins and modern humans (the rest of the samples), to verify the external enamel surface and the enamel dentin junction. Most of the TD6 molars express absence or discontinuity in the trigonid crests. The results show that H. antecessor presents median trigonid crests, although less frequently than other Eurasian hominids, suggesting that this feature is not a Neanderthal apomorphy as it is not exclusive to this species. The data support the hypothesis that the settlement of Europe may have been the result of several migrations, at different times, coming from the “same source population” located in Western Eurasia. The H. antecessor may have been a group from this source population that settled in westernmost Europe during the Early Pleistocene.

In 2020, it was possible to obtain peptide fragments from the dental enamel of H. antecessor and it was shown that these hominins belonged to a closely related lineage with hominins of the Middle and Late Pleistocene, including modern humans, Neanderthals and Denisovans. Paleoproteomic studies by Enrico Capellini using a mass spectrometer have allowed the identification of a significant amount of the organic protein matrix of the enamel of a small tooth fragment. The H. antecessor had a peculiar amino acid sequence in its dental proteins, which reinforced its identity as a species, while also linking it closely to Neanderthals, H. sapiens and the Denisovans. These results have been confirmed by a second laboratory at Pompeu Fabra University and CSIC in Barcelona.

Dental morphology is very similar to that of H. erectus. In the mandible the canine fossa is present, absent in the H. erectus from Asia. The lower M1 is similar to the HSAM. The thick enamel on permanent molars is similar to extinct and extant Homos. The percentage of dentin in the total crown is similar to the values obtained from low modern humans, but higher on the lateral, close to the Neanderthal. The teeth exhibit large dimensions of coronal and root dentin, as well as a thin enamel pattern, which has traditionally been considered a Neanderthal autapomorphy. For María Martinón et al. (2019), the evaluation of the dental sample supports the taxonomic validity of H. ancestor.

In summary, we can say:

• Primitive denture characters include robust teeth, premolars with multiple and incisive roots in the upper jaw.
• Derivative characters include canines and some previous teeth reduced in size.
• Tooth eruption patterns seem to be similar to modern humans, suggesting the same development rates.
• Mandible without a chin.
• The lower jaw is thinner than the lower jaw H. ergaster and H. habilis.
• Postcan teeth are smaller than in H. habiliswithin the range H. ergaster, H. erectus and H. heidelbergensis.

Facial morphology

Head of a child H. predecessor at the Museum of Natural History of London.

The facial anatomy of H. antecessor, although incomplete, has been known since 1997, mainly from the dental and craniofacial remains of the immature individual ATD6-69 from Gran Dolina, from 0.78-0.90 Ma, corresponding to an individual 10-11 years old.,5 years. Its facial morphology was the hallmark for defining a new species and presenting it as the possible common ancestor of H. neanderthalensis and H. sapiens. This ATD6-69 morphology falls within the range of variability of modern humans and archaic humans of the Middle Pleistocene of East Asia, as opposed to archaic humans or Neanderthals of western Eurasia or the Middle Pleistocene. African. The most notable features are a completely flat face, a coronal orientation of the infraorbital surface, a curved zygomaticoalveolar ridge (the bone that connects the cheek to the tooth-bearing part of the maxilla), an outward projecting nose, and the presence of a very marked canine fossa. The research team led by Dr. Arsuaga concluded that certain characters derived from facial topography were different from the primitive ones of the Homo clade. The jaws of the H. antecessor are smaller than those of African Homo specimens, or European Middle Pleistocene hominins or Neanderthals. The TD6 and Zhoukoudian hominins are the only ones with a projecting zygomaxillary tubercle. On the other hand, TD6 hominins share with Neanderthals and extant humans a convex upper edge of the temporal scale, as well as a near-vertical anterior position of the incisor canal.

ATD6-96 jaw of a young woman.

Note that when the ATD6-96 mandible was found in 2003, many of its features were already found in H. erectus, which led some authors to suggest that H. antecessor was a European geographic variant of H. erectus “Classic.”

Doubts about facial morphology stem from the fact that it has been defined based solely on a subadult specimen. In 2013, anthropologist Sarah Freidline and her colleagues statistically determined that previously evoked characteristics would not disappear with maturity. H. antecessor suggests that the modern human face evolved and disappeared several times in the past, which is not unlikely, as facial anatomy is strongly influenced by diet and thus environment.

H. antecessor has a unique combination of features in facial morphology, with derived modern features including a modern-looking canine fossa, with a “hollow” cheekbone and protruding nose, and archaic features with a low forehead and arch. superciliary marked, similar to H. erectus and Neanderthals, and a protruding occipital bun at the back of the skull.

Torso

Nine ribs belonging to at least three young individuals of the Homo antecessor species have been recovered at the TD6 level of the Lower Pleistocene of the paleontological site of Gran Dolina, in the Sierra de Atapuerca. Among these fossils, the following stand out:

• ATD6-97, tenth left rib, very fragmented, and without a determined age.
• ATD6-39, tenth right rib, in twelve fragments, of a young man of about 12 years.
• ATD6-66, third or fourth left rib, and ATD6-88, fourth or fifth right rib, which could correspond to the same 18-year-old individual.
• ATD6-79, second right rib, at least 12 years old, and ATD6-108, first rib right, in five fragments of a 14-year-old. Based on the estimated age, and the size and degree of development of the insertion for the serrate muscles, it can be indicated that both correspond to the same individual, 14 years after his death.
• ATD6-85, eighth or tenth right rib, in nine fragments, of a teenager or young adult.
• ATD6-89 and ATD6-206, seventh left rib, in six fragments of a young man of a minimum age of 11 years.
• ATD6-251, tenth right rib, with almost the entire axis, fragmented into six remains, of an immature individual.

Fossil remains of clavicles have also been recovered, among which we highlight

• ATD6-50 long and thin collarbone (although thick about the current human) with pronounced shaft curvature and small epiphysis, similar to the neandertalThat could correspond to a male.
• ATD6-43, an adult radio (earm bone) that could be male by its size, or female by its gracility.

Regarding the size of the thorax of TD6 hominins, we only have a single thoracic midrib (ATD6-89 and ATD6-206) and two clavicles (ATD6-50 and ATD6-37) to estimate it. The length of these is related to the width of the upper torso. A comparative study has been carried out with a sample that includes modern humans, Neanderthals and H.ergaster. Based on the current Homo antecessor rib record, the hypothesis that this species had a large thorax similar to that of Neanderthals, who have a thoracic capacity and lung volume 20% greater than modern humans. But the rib record and long clavicles support the hypothesis that H. antecessor, like Neanderthals, had a broader thorax than modern humans, which could correspond to a primitive bauplan body, linked to wide and heavy bodies inherited from their Pleistocene ancestor Medium.

Two atlases (the first cervical vertebra) have also been recovered and are indistinguishable from those of modern humans. For the axis (second cervical vertebra), the angle of the spinous process (protruding from the vertebra) is about 19º, comparable with Neanderthals and modern humans, and diverging from the 8º of H. ergaster. The sternum is narrow. The acromion is small. The scapula is similar to all Homos, indicating that H. antecessor was not as skilled a climber as apes or pre-erectus species, but was capable of effectively throwing projectiles, such as stones or spears. The vertebral foramen which houses the spinal cord spinal cord, is narrow compared to modern humans. The spine as a whole aligns with modern humans.

Limbs

Conclusions from studies of the hands and feet suggest that TD6 hominins exhibit a morphology more similar to modern humans than to Neanderthals and their predecessors from the European Middle Pleistocene. Among the fossils related to the extremities in Gran Dolina, the following stand out:

• Higher:
  • ATD6-22 and ATD6-43, radio fragments, the second almost complete.
  • ATD6-121 child humerus.
  • ATD6-148 Left humerus of vigorous young man, “Rafa”, in which evidence is seen of having been fragmented to get the marrow from his interior. Discard marks and rupture of the condiles to separate the muscle masses. Like the ATD6-121, large olecran pit and very fine lateral and medial pillars, such as the hominids of the European Middle Pleistocene, the neandertales and Bodo's.

The incomplete radius ATD6-43 is unusually long (257 mm) and straight for someone living so far north, and is reminiscent of early modern humans and tropical populations, versus the Neanderthals of shorter limbs. It could indicate a high brachial index (length ratio between the radius and the humerus) and proportions closer to H. ergaster and modern humans than pre-Neanderthals and Neanderthals. The cross section of the radial axis is quite round and graceful throughout its length. As in archaic humans, the radial neck near the elbow is long, giving the biceps brachii more strength. The radial tuberosity (a bony protrusion that protrudes below the radial neck) is positioned to the frontal side when the arm faces outward, as in modern humans and the H. heidelbergensis, unlike Neanderthals or more archaic hominins.

• Lower extremities:
  • ATD6-56 left kneecap associated with right kneecap ATD6-22with evidence of trauma.
  • ATD6-95 and ATD6-70+107 almost complete left and 2nd right metatarsian perhaps of an adult male. The astrágalo is long and high, with long and wide throccles and with a short neck.
  • ATD6-124 Parts of the 4th right metatarsian. The bone was welding after a break when he died. This fracture suggests that the population would travel long distances or travel through uneven terrain.

The ankle joint is adapted to withstand high stresses (study based on ATD6-95 and ATD6-124 fossils), which may indicate a heavy and robust body plan, much like that of Neanderthals (Pablos, 2012).

Like other archaic humans, the femur presents a developed trochanteric fossa and a posterior crest, highly variable features among modern humans. The two known patellas, ATD6-22 and 56, are subrectangular rather than subtriangular in shape, although they are narrower than in modern humans. They are small and fine, especially in females. The apex of the patella (the area that does not attach to another bone) is not well developed, leaving little attachment for the patellar tendon. The median and lateral aspects of the knee joint are similar in ATD6-56, with the median being larger in ATD6-22, while the lateral is usually larger in modern humans.

The phalanges and metatarsals of the foot are comparable to modern humans, but the phalanx of the great toe is quite robust, perhaps related to the way the H. antecessor rose from the ground. The talus (ankle bone) is exceptionally long and high, as is the face that connects to the leg (trochlea), perhaps because of the way in which body weight was transmitted. The long trochlea caused a short neck of the talus, which connects the head of the talus to the toes and the body of the talus to the leg. This seems similar to the case of Neanderthals, as a response to a heavy and stocky body, to relieve further stress on the articular cartilage in the ankle joint. This would also have allowed for more flex.

Structure and life cycle of Homo antecessor

Most of the analyzed remains of H. antecessor correspond to subadult or infant individuals, so part of what follows corresponds to inferences.

The size and shape of the body was similar to modern humans, but more robust, with a broader trunk. A large majority of individuals would measure between 160 and 180 cm, with the average for males being somewhat higher than for females. females, as in the case of modern humans.

The adult male clavicle specimen, ATD6-50, has been estimated to have measured between 162 and 187 cm (mean 174.5 cm), based on the comparison between clavicle length and stature of the modern Indian population. The adult ray ATD6-43 would have belonged to an individual 172.5 cm tall based on comparison of radial length and stature among several modern populations. Based on the metatarsal foot bone, it is estimated that a male H. antecessor measured 173 cm, and a female 169 cm, compared to an average of 163.5 cm for western European Neanderthals, and 178.4 cm for early European humans modern.

Regarding the life cycle of H. antecessor, a delivery similar to H. sapiens in terms of physiology, child movements and mode of presentation, but with a more comfortable transit through the birth canal due to larger dimensions of the pelvis, although evidence of a complete pelvis is lacking. Lactation would last between 3 and 4 years. Development would probably be almost as long and complex as in our species, with infancy, childhood, juvenile stage, and adolescence, including a pubertal spurt of similar intensity to ours.

In 2010, individual ATD6-112, represented by a permanent upper and lower first molar, was estimated to have died between 5.3 and 6.6 years of age based on chimpanzee tooth formation rates (low estimate) and modern humans (low). The molars are barely worn down, meaning that the individual died shortly after the tooth erupted and that the first molar erupted at this age. The age is within the range of variation of the modern human, and could indicate that the H. antecessor had a long childhood, a characteristic of modern humans in which significant cognitive development takes place.

Its longevity was less than that of H. sapiens. His lifestyle would not allow for a life beyond the age of 40 or 45. Life expectancy at birth would be between fifteen and twenty years. Among the possible causes of death we can find: childbirth, wound and oral cavity infections, trauma caused by accidental blows or intraspecific violence, or by predators.

Pathologies

Some of the fossils recovered from ATD6 show pathological bone manifestations. Some of these pathologies are listed below:

• The partial face of the ATD6-69 has an ectopian M3 (third molar upper left) that erupted incorrectly, causing impact and blocking M2. The impact of M3 is quite common in modern humans (up to 50% in some populations), but is rare in M2 (0.08 to 2.3%). The impact can lead to secondary lesions, such as dental decay, radicular reabsorption, dentigerous cysts or keratoquistes.
• The ATE9-1 jaw has severe dental wear, abrasion of the crowns of the teeth and bone reabsorption in the root, so that the root canals of the canines are exposed. The trauma is consistent with gum disease due to tooth overload for having used the mouth to transport objects. This condition was also found in later remains of the Sima de los Huesos.
• The left ATD6-56 has a 4.7 mm x 15 mm osteophyte (bone extracts) on the lower margin. Osteophytes are usually formed in response to the stress of osteoarthritis, resulting from aging or an inadequate load of the joint due to bone desalination or the latitude of ligaments. In the case of ATD6-56, the wrong load was perhaps the cause. Putting on cradles and kneeling frequently can cause this condition, but if the right knee bone ATD6-22 (which does not have this trauma) belongs to the same individual, then it is unlikely that this is the cause. If so, the injury could be caused by a local trauma, such as a tension in the soft tissue around the joint due to a high-intensity activity, or a fracture of the left femur and/or the tibia, which cannot be confirmed as these bones are not associated with this individual.
• The fourth right metatarsian ATD6-124 has a lesion of 25.8 mm x 8 mm on the medial side (make the middle line of the bone) compatible with a break, which is usually found in soldiers, long distance corridors or people with flat feet, whose bones fail due to high intensity repetitive activity. Them neandertales later developed a more robust lower skeleton to resist such movement through irregular terrain. Another example of the condition in the Sima de los Huesos has been identified in archaic humans, so it is believed that these breakages were a common injury to them because the fracture cured does not leave a visible mark, and due to its alleged high-intensity lifestyle.

Morphological characteristics of Homo antecessor

In summary, Homo antecessor is characterized by a unique combination of plesiomorphic and derived features:

• Plesiomorphic (primitive characteristics) .
  • Dentition.
  • Endocranial traits of the parietals.
  • Front huidiza and double arch supraorbital bull.
  • The styleid process is merged to basics.
  • Nose floor tilted.
  • Brass absence.
  • Position of the Mentonian foramen at the level of mandibular P3-P4.
  • Low position of the milohioid line regarding alveolar margin at the mandibular M3 level.
  • Little deep pterigoid.

• Apomorphous (derivative characteristics) shared with hominini post .
  • Double arched supraorbital torus.
  • Parasagital flattening of the upper surfaces in the pacifiers.
  • Position of lateral prominence at the level of the mandibular M2 heel. Absence of alveolar prominence. Trigonum postmolare bent obliquely. Small butterfly and smooth something deeper. Regular gonion profile. Ratio length / width of the mandibular alveolar arch below 100.
  • Permanent bucolingually expanded mandibular incisives Homo habilis and others hominini of the Lower Pleistocene. P3/2003/P4 for the coronal area of premolars. Smaller postcanine teeth than in H. habilis and similar to H. ergaster, H. erectus and hominini Europeans of the Middle Pleistocene. M3 mandibular reduced compared to M1 and M2.
  • Radial tuberoses confronted anteromexically.
  • The pattern of facial remodeling on ontogenia.
  • Dental ontgenia.

• Characteristics derived, shared with neandertales and HSAM .
  • Convex upper edge of the time scale, and an earlier position of the incisive duct, which is almost vertical (Arsuaga, 1999).
  • Planum alveolare absent or weak.
  • Cranial capacity estimated at more than 1000 cm³.

• Characteristics derived, shared with HSAM .
  • The most modern face than African hominids of Pleistocene Inferior, with prognatism pronounced. It is flat, with an outgoing nose, slightly projected maxillary and thin jaw. Canine fry by reorientation forward and under the infraorbitary plates whose edge lower part of a horizontal and high position.
  • Average position of the deepest point of the mandibular cleft.
  • It rhotulates somewhat narrow, with high rotulian indices.

• Characteristics derived, shared with neandertales and preneandertales from the Sima de los Huesos.
  • Presence of a medial pterigoid tube.
  • Reinforced and compressed occlusal polygon, and a permanently biased external M1 contour with lumped hypoconus protuberance.
  • The mastoid region is a reminiscent of neandertal.
  • Permanent upper incisors with a shovel shape, especially I2.
  • Average crest presence of the trigonide.
  • Large olecranial pit and very fine medium and lateral pillars.
  • Very long, thin (poca robustness), curved in the axis and small epiphysis.
  • Tracle of the narrow astral.

Cultural context of Homo antecessor

We will consider the type of lithic industry used by H. antecessor, the paleohabitat in which they inhabited, and the type of diet they ate, including signs of cannibalism.

Technology

Several lithic assemblages have been recovered in the Sierra de Atapuerca (Spain), at various levels of the Sima del Elefante, Gran Dolina, Galería and Sima de los Huesos, which allow us to reconstruct the evolution of technology on a local scale during the Early and Middle Pleistocene:

• First population at TE9 and TD3-TD4 levels by Homo sp, of 1,2 Ma, with a very primitive mode 1 technology to take advantage of corpses fallen in cavities.
• The first cultural phase was revealed at the TD6 level before 800 ka, with new livelihood and technology strategies Homo antecessor, still from Mode 1 or olduvayense, with absence of hand axes. Here, the critique assembly is rich and diversified. The production chain for lytic manufacturing is intuited: nuclei, lascas, useful, fragments as a result of the activity of the size. Use to cut meat, prepare bones to break them, uncut and raer wood, and likely skin treatment. TD6 documented hunting activities and the first trace of cannibalism in prehistory.
• The second cultural phase corresponds to the preneandertales Sima de los Huesos, Galería y TD10, 500 to 300 ka, with Modo 2 or Achelense technology to process corpses.
• The TD10.1 level can represent the local evolution of the Mode 2 technique to Mode 3.

A comprehensive study has been performed on the lytic assembly of the entire TD6 sequence. The archaeo-paleontological record of TD6 consists of more than 9,000 faunal remains, 443 coprolites, 1,046 lithic pieces, 170 hominid remains and 91 Celtis seeds. There seem to be two main stages of occupation. In the oldest subunit, TD6-3, both the type of pieces and their scarcity show the light and infrequent hominid occupation of the cave, while in subunits TD6-2 and TD6-1 the remains are rich and varied, which It may reflect that the Gran Dolina cave became a landmark in the region. However, the TD6 lithic assemblage is extremely homogeneous throughout the stratigraphy: the cores were woven in the same way, and the kneading products and tools have similar characteristics.

Some of the lytic industry parts of the TD6-2 level.

H. antecessor produced simple stone tools in Gran Dolina. This industry is found in other parts of the Early Pleistocene in Spain, and is distinguished by the preparation and sharpening of cores before husking them, the presence of crude bifaces, and a certain standardization of tools. It is therefore an ancestor technique of the Acheulean industry. The use of the TD6 stone tools is consistent with repeated grinding against meat, so they were probably used as butchery implements.

In subunit TD6-3, 84 stone tools were recovered, mostly small unmodified quartzite pebbles, with percussion damage from striking items such as bone, rather than using more specialized implements. 41% of these assemblages are flakes, some coarse and large (average 38 x 30 x 11 mm), the result of rudimentary stone carving skills or the use of poor quality materials to work them. They used the unipolar longitudinal method, flaking only one side of a core, probably to compensate for a lack of advance planning, opting to carve irregularly shaped and therefore poorer quality pebbles.

In subunit TD6-2, 831 stone tools were found, with a greater variety of materials (although the majority were flint), which indicates that they were moving further away from the cave in search of better raw material. Less than 3 km from Gran Dolina, we find, in addition to flint and quartz, quartzite, sandstone and limestone, minerals suitable for making stone tools. They produced fewer pebbles and cut more flakes, although they did not economize on material, since half the cores could have produced more flakes. Also, they modified certain jagged blocks to make them more manageable. This advance planning allowed them to use the centripetal method (flaking only the edges of the nucleus) and the bipolar method (place the nucleus on an anvil and strike it with a stone hammer). There are 62 flakes of less than 20 mm, and 28 of more than 60 mm. There are 3 high quality flakes, perhaps from the same person. There are also tweaked tools: notches, spines, denticulate tools, points, scrapers, and a single chopper. They are rare small tools from the European Early Pleistocene.

In subunit TD6-1, 124 tools were found, but in poor condition, since hyenas had used this area as a latrine. There are no pebbles or cores, and 44 tools are unidentified. The flakes are small (average 28 x 27 x 11 mm), with 10 smaller than 20 mm and only 3 larger than 60 mm. The methods seem to be the same as TD6-2. Only the 14 largest flakes (average 35 x 26 x 14 mm) were retouched: 1 marginally retouched flake, 1 notch, 3 stone spines, 7 toothed lateral scrapers, and 1 toothed stone point.

Paleohabitat

Only a few charcoal particles have been recovered from TD6, probably from a fire that started outside the cave. There is no evidence of the use of fire or burning bones (cooking) in the occupation sequences of the Gran Dolina. In other parts of the world, the use of fire did not appear until about 400,000 years ago. Rather than use fire, these early Europeans must have resisted the cold physiologically, perhaps through a high-protein diet to support a fast metabolism. They may have worn fur coats to keep out the cold.

The Homo predecessor must have moved along the Ebro River, with the Sierra de Atapuerca near its sources.

From the associated fauna group in Atapuerca, it can be deduced an environment of open forest or with a nearby meadow and a nearby pool or lagoon, with a warm climate, with seasonal humidity; climatic conditions similar to present-day winters in the area. These climatic conditions changed 600 to 500 ka ago, when they became relatively harsh and cold, causing European humans to develop Neanderthal-like features, many of which appear to be adaptations to colder environments.

The climate 800 ka ago would have been similar to today, with an average cold temperature of 2 °C in December and January, and a warm 18 °C in July and August. There could be freezing temperatures between November and March, but the presence of olive and oak trees suggests that such temperatures were rare. However, the occupation sequences of TD6 appear to have been a few degrees warmer than today, and H. antecessor probably migrated from the Mediterranean coast to the interior of Iberia when colder glacial periods were transitioning to warmer interglacials, and warmer grasslands dominated. It is probable that they followed the water courses during the migration, and in the case of the Sierra de Atapuerca, most likely the Ebro river.

The remains of TE9 at Sima del Elefante also indicate a generally warm climate.

Finally, Happisburgh tracks were found in estuarine marshes with open woodlands of pine, fir, birch, and in wetter areas, alder with heather shrubs and grasslands; the vegetation is consistent with the beginning of a colder period or the end of an interglacial.

Food

The Gran Dolina site seems to correspond to a long-term settlement, a base camp. Hominin activity outside the cave, but close to it, has been proposed. The excellent taphonomic preservation of the bones indicates a very short time to external exposure, rapid transport and very short distances. One consequence of this hypothesis is that the dating of the fossils could be older than previously assumed.

They were hunters and gatherers of small animals, eggs, and all kinds of edible wild plants. They used different strategies to hunt, they were organized in clans of 15 to 40 hierarchical individuals and they transported the pieces in different ways, selecting or not according to their size, the time of day, the distance to the base or the presence of other carnivores in the environment.. From these facts we can infer a great social complexity in the distribution of tasks. There were sporadic contacts with other groups to avoid inbreeding. The presence of ribs (which are eaten by large predators) and cut marks made with stone knives allow us to deduce that they killed these animals themselves.

The faunal remains recovered from TD3-4-6 of Gran Dolina and Sima del Elefante (levels 9 -14) have been studied. Fauna remains abound from hunting activities, with cut marks on skeletal remains, systematically fragmented by anthropic action. Subsistence strategies ensured that hominin groups survived and reproduced in sufficient numbers that these early humans maintained a continuous occupation of Europe.

In the Gran Dolina, fossils of 16 animal species have been recovered, including several extinct species (the great-horned deer Eucladoceros, the fallow deer Dama valonetensi, the red deer Cervus elaphus acoronatus, bison Bison voigstedtensi, rhinoceros Stephanorhinus etruscus, horse Equus stenonis, fox i>Vulpes praeglacialis, bear Ursus dolinensis, wolf Canis mosbachensis), spotted hyena, wild boar, and several undetermined species of mammoth, monkey, and lynx. Some specimens exhibit cut marks consistent with butchery practices, and 13% of the remains from Gran Dolina show evidence of human modification. 106 specimens of deer appear. Hominins appear to have transported the entire carcasses of the small animals, and the limbs and skulls of the larger ones. This indicates that the H. antecessor sent out hunting parties that killed and brought back game to share with the entire group, demonstrating social cooperation and division of labor. Only 5% of the remains show damage from carnivorous animals, which could indicate scavenging activity on their part.

In the Sima del Elefante there are also remains of other species, with some long bones of large mammals cracked, presumably to access the bone marrow. Others show evidence of percussion and fleshing. There are also remains of Hermann's tortoise.

The cool and humid montane environment fostered the growth of olive, mastic, beech, hazelnut and chestnut trees, which H. antecessor may have used as a food source, although they become more common on TD7 and TD8 as the interglacial progresses and the environment becomes wetter. In unit TD6, pollen comes mainly from juniper and oak. Trees would have grown along rivers and streams, while hills and ridges were dominated by grasses. TD6 individuals appear to have also consumed hackberry (Celtic) berries, which have historically been used for their medicinal properties, rather than as food. food for its little meat.

There is no evidence that H. antecessor could handle fire and cook, and wear on molars indicates greater consumption of gritty-textured and mechanically challenging foods than later species, such as raw rather than cooked meat and underground storage stems. From their hygiene we know that they used toothpicks to clean the interdental spaces.

Cannibalism

Eighty remains of young adults and children of H. antecessor from Gran Dolina exhibit cut marks and fractures similar to those of other animals, made with stone implements, indicative of cannibalism, and are the second most common remains with evidence of slaughter. Efficient use of these human bodies can explain why most of the bones are broken or damaged. There are no complete skulls, elements of the face and back of the skull have been percussed and the muscle attachments on the face and base of the skull have been severed. The facial break was probably to gain access to the brain. He must have hit the crown of his head, causing impact scars on his teeth at the gum line. Several skull fragments show desquamation.

The ribs also have cut marks at muscle attachments consistent with disembowelment, and ATD6-39 has cuts along the rib in the same direction. The neck muscles were severed and the head and neck separated from the body. The vertebrae were often cut, peeled, and struck. The muscles of all the clavicles were cut to separate the shoulder. One spoke, ATD6-43, was cut and peeled. The femur was shattered to remove the bone marrow. The hands and feet variably exhibit percussion, cut, or scaling, likely the result of dismemberment.

In short, the meatiest areas were prepared and the rest was discarded. This suggests human sacrifice for nutritional purposes (perhaps in extreme circumstances), but the face shows more cut marks than those of the animals. When this is seen in modern prehistoric human specimens, it is interpreted as evidence of exocannibalism, the custom of feeding on people from alien social groups, such as an enemy of a neighboring tribe. A possible interpretation of this abundance of cuts on the face in H. antecessor would be the difference in the structure of the muscular joints between humans and animal prey, which would require more cuts for the human face, or the fact that butchers were less familiar with butchering humans.

However, H. antecessor is very abundant among those sacrificed, and the group is composed mainly of young adults, without older individuals. In 2010, it was hypothesized that they were practicing exocannibalism and hunting members of neighboring tribes. According to another analysis, the environment of H. antecessor was very rich in resources, with an empty niche for predators, and hominids could continuously supply themselves with abundant meat and fat, so starvation must be ruled out as a cause of cannibalism. They could be victims of territorial disputes of a structural nature. In 2019, other paleoanthropologists argued that demography can be explained as the consumption of tribesmen who had already died of natural causes, and to avoid wasting valuable food, especially considering the high young mortality rate of these groups. This hypothesis is called "cultural cannibalism".

Taxonomy

In the eighties of the s. XX changed the interpretation of the fossil record of hominids, which meant the partition of some hypodigms into different and well-defined species. The paradigm of an anagenetic evolution of the genus Homo in three evolutionary degrees, not always well differentiated, gave way to a more complex model with a greater number of species and a contemporaneity of different evolutionary lines and the extinction of all species. lineages, except that of H. sapiens. This produced two interrelated problems: defining the concept of species (this biological concept cannot be applied to paleontological investigations) and choosing the appropriate method to recognize paleospecies in the fossil record. Define a long list of qualitative and quantitative skeletal and dental characters, the variation of which can be compared with that of current species, and which allow the basic taxonomic units to be recognized in a certain set of fossil remains. Cladistics was then introduced into human evolution, a phylogenetic species concept born of the evolutionary process itself. The characters are not static elements, but the result of the evolutionary process. Some researchers have proposed recognizing fossil species by the use of uniquely derived characters, but others believe that a paleospecies can be accepted if a unique set or combination of characters can be distinguished, even if we do not know its "cladistic status".

In the 1990s there was a debate about human occupation in Europe: short chronology with late occupation or long chronology. The Dutch and English schools believed that Europe was not populated before 500 ka, due to the low cognitive abilities of the hominins of that time, who did not master fire. In 1994, human remains were found at level TD6 of Gran Dolina. Paleomagnetism studies showed a polarity change between the TD8 and TD7 levels corresponding to the reversal of the Earth's magnetic pole, or the so-called Brunhes-Matuyama limit (M/B limit). Below TD-8 the sediments and fossils were from the Lower Pleistocene, 790 ka, proving that human occupation in Europe occurred before the Mimomys-Arvicola limit of molar shedding in water voles. The subsequent finding in England of 700 ka lithic industry at Pakefield and human footprints on Happisburg beach 850 ka ago marked the end of the short chronology hypothesis.

Taphonomy

Excavations from 2003 to 2007 revealed a more complex stratigraphy than previously thought, and TD6 was divided into 3 subunits encompassing 13 layers and 9 sedimentary facies (rock bodies distinct from adjacent bodies). Human presence is recorded in subunits 1 and 2, and in facies A, D1, and F. Scattered bones were found in the D1 facies of the TD6-2.2 layer, and in the F facies of the TD6-2.2 and TD6 layers. -2.3, but in facies D they seem to have grouped mainly in the northwest area. This could indicate that they were swept into the cave through a debris flow. As for facies F, which contains most of the human remains, they may have been deposited by a low-energy debris flow (floodplain type) from the main northwest entrance, and by a stronger flow from another entrance to the north-west. south. Fossils deposited by water were also recovered from facies A in the TD6-2.2, TD6-2.1, and TD6-1.2 layers. Therefore, it is possible that H. antecessor did not inhabit the cave, although it would have been active near it. Only 5.6% of the fossils show evidence of weathering in the open air, by roots and soil, which could mean they were deposited deep in the cave shortly after death.

Dating

Human occupation appears to correspond to a warm, humid savannah habitat, during transitions from cold glacial to warm interglacial periods, after the climate warmed, and before forests expanded to dominate the landscape. This it is consistent with analyzes of pollen and study of the fossil record of amphibians and scaly reptiles. The change in polarity between TD7 and TD8 (M/B boundary), indicated that TD8-TD11 levels were deposited during the Middle Pleistocene, and TD1-TD7 levels during the Lower Pleistocene, which is consistent with changes in the fossil record..

In 1999, two ungulate teeth from TD6 were dated using uranium-thorium dating to 794 to 668 ka, and paleomagnetically to before 780 ka. Later, in 2008, Sima del Elefante level TE9 was dated to 1.2-1.1 Ma using paleomagnetism and "surface exposure dating". Subsequently, in 2013, ATD6-69 was dated to between 930 and 780 ka using paleomagnetism, in addition to uranium-thorium and ESR dating (electron spin resonance dating) in more teeth. The thermoluminescence (TL) age at one meter below M/B Inversion is 960 + 120 ka, which may correspond to MIS level 25 (Marine Isotope Stages method). Another systematic dating used the ESR method on optically bleached quartz grains: 6 samples from TD6 and TD7 gave an age of 800 to 880 ka, suggesting that human settlement was deposited during MIS 21. Finally, in 2018, dating ESR of specimen ATD6-92 of H. antecessor gave an age of 600+90 ka to 950+90 ka, while paleomagnetically it was restricted to before 772 ka because it was below the M/B limit, so TD6 hominins belong to the MIS level 21.

Classification and phylogeny

The definition of H. antecessor as a new species by its discoverers is based on the remains found since 1994 at the TD6 level of the Gran Dolina site, in the Sierra de Atapuerca, and which date from at least 800 ka according to paleomagnetic measurements, with a unique combination of characters in this population. The holotype of the first description was based on a fragment of the lower right jaw with three molars (ATD6-5), a fragment of the upper jaw (ATD6-13), and 12 other teeth attributed to the same individual.

The facial morphology is similar to that of Homo sapiens, with a coronal orientation and a slight backward inclination of the infraorbital plate, which determines the presence of a very conspicuous canine fossa. The lower edge of this plate is horizontal and slightly arched. The superciliary arch is double arched and the encephalic capacity, estimated from an incomplete fragment of the frontal bone, indicates a figure greater than 1000 cm³.

This modern face with primitive dentition led the Atapuerca team to propose a new human species, Homo antecessor. Early dental features included, among others, the development of a cingulum on premolars and molars, profuse enamel crenulations, asymmetry of the lower first premolar crown, large molars, and complex and robust root systems.

However, this population presented traits derived from other Lower Pleistocene fossils, such as an increased cranial capacity indicated, and a “modern” craniofacial architecture, (faces of adolescent ATD6-69 and adults ATD6-19 and ATD6-58) different from the primitives of early Homo and H. ergaster, and without pronounced prognathism. In addition, its pattern of dental development is modern, which would later be inherited by H. neanderthalensis and H. sapiens.

While H. erectus has a facial growth pattern similar to that of early Homo and Australopithecus, both in H. antecessor as H. sapiens, bone resorption predominates during facial growth. Comparison of bone deposition and resorption patterns of KNM-WT 15000 (the Turkana boy – H. ergaster) and ATD6-69, show that the facial bone growth of H. antecessor is similar to modern humans, while that of the Turkana child is similar to that of chimpanzees. The similarities between the subnasal anatomy of H. antecessor and H. sapiens suggest that the “modernization” of the face was clearly already underway in H. ancestor.

It was proposed to H. antecessor as the best candidate for UAC of modern human and Neanderthal populations, due to three synapomorphies shared among the three groups: a tall and convex temporal bone scale, a vertical and anterior incisor canal, and a marked nasal prominence. These anatomical and biological characters of H. antecessor pointed to a speciation event prior to the origin of H. sapiens and the neanderthal.

In 2001, it was postulated that the remains from Gran Dolina and those from the Tighennif site in Algeria (classified as H. ergaster) represented the same population, since 14 of the 15 dental features listed by Bermúdez de Castro and his collaborators for H. antecessor had been identified in the Middle Pleistocene of North Africa, which could mean that both would correspond to H. mauritanicus. This study showed that the Tighennif remains were larger than those of H. antecessor, and dentally similar to other African populations. They recommended housing all North African Early Pleistocene specimens as H. ergaster mauritanicus.

Starting in 2005, the hypodigma of H increased. antecessor and it was seen that there were more similarities between the European and Asian fossils than with the African ones. Further analysis of ATD6-96 and ATD6-113 revealed similarities to H. erectus from China, especially in gracefulness and dimensions, with fossils from Nanking, Dali and Zhoukoudian. The fossil record suggested that there were more links to Pleistocene humans in Asia than to those in Africa.

In 2007, María Martinón carried out a detailed phenetic and cladistic study of more than 5000 dental pieces of all the species of the genus Australopithecus and Homo. She identified herself:

• an African dental block: A. africanus, A. afarensis, H. habilis, H. ergaster and H. mauritanicus, with increased accessory cuspides in later teething and complicated occlusal surface,
• a Euro-Asian dental block: H. predecessor, H. erectus, H. heidelbergensis and H. neanderthalensis with particular characteristics in the previous dentition (triangular palate shape, pronounced lip convexity and occlusal surface in V), and in the subsequent dentition (reds derived from tooth reduction such as loss of molar cuspids, simplification of occlusal surfaces, or appearance of patterns of grooves other than the driopitecino), in addition to average crest of the continuous trigonid and transverse crest as the neandertales,
• intermediate position H. sapiens and H. georgicus.

This implies independent evolutionary paths between Eurasia and Africa, and perhaps a Eurasian origin for H. predecessor. In addition, certain features considered typical of Neanderthals, could not be Neanderthals apomorphies but primitive characteristics already existing in H. ancestor.

In 2007 the legitimacy of H. antecessor as a separate species because a large part of the anatomy of the skull is unknown, because H. heidelbergensis at the same time and region, and for being based on the remains of a child, whose presumed features might have disappeared with maturity; the restructuring of the face could have been caused by regional climatic adaptation rather than speciation. It was also postulated that H. antecessor was a branch of H. ergaster from Africa, which disappeared after an unsuccessful attempt to colonize southern Europe. /i>. In 2016 it was estimated that the separation between the H. neanderthalensis and HSAM occurred 806-447 ka for Y-DNA, dates that fall within the H range. antecessor and outside of H. heidelbergensis.

In 2017 the Atapuerca team analyzed the study that suggested that the modern human face evolved independently several times within the genus Homo. The study was carried out in light of the TD6 fossils, basing his interpretation on the absence of a fully modern face in Middle Pleistocene Africa. Due to the absence of fossils, only Kabwe and Bodo were taken into account (the characteristics of the infraorbital of the latter allow it to be aligned with H. sapiens). Finally, the Atapuerca team admitted that H. antecessor may not be a modern human ancestor, although it probably diverged shortly before the split between modern man and Neanderthal. They propose a cladogenesis of the genus Homo during the Lower Pleistocene that gave rise to an increase in cranial size and a modern facial morphology:

• KNM-WT 15000 (H. ergaster) represents the primitive condition of the nail Homo.
• H. predecessor probably derives from this cladogenesis and represents a side branch confined to Western Europe (BdC et al. 2003 and 2012; Carbonell 2005; Martinon-Torres 2007). H. predecessor shares deriving conditions shared with neandertalesthe Homos of the Middle Pleistocene of China and sapiensand it would be near the most recent common ancestor.
• Media-facial prognatism neandertales (Rak, 1986) and the hominids of the Pleistocene of Eastern Europe, would represent another derivative condition that could have arisen from a face similar to modern (Arsuaga, 1999). These traits were retained by the neandertales (sinapomorphous).
• The specimen of Bodo presents some sympathies with neandertales and HSAM in various degrees and could be part of one of the lineages of the cladogenesis that in Africa led to H. sapiens and in Europe to H. neanderthalensis.

In 2020, geneticist Welker and colleagues analyzed ancient proteins collected from the enamel of molar ATD6-92 and compared them with the proteome of Homo georgicus remains from Dmanisi, Georgia, obtaining evidence of that H. antecessor is a sister lineage that belonged to the same group as Neanderthals, Denisovans and Homo sapiens. This location implies that the modern face of H. antecessor, similar to modern humans, may have deep ancestry in the genus Homo, and that the Neanderthal cranial morphology represents a derived form.

The morphology of the jaw is reminiscent of that of certain much later hominids from the Middle Pleistocene, of the species Homo heidelbergensis, such as those from the Sima de los Huesos in Atapuerca. The postcranial skeleton indicates a certain gracefulness compared to the robustness of H. neanderthalensis from the second half of the Middle Pleistocene.

The scientific controversy is related, as in the findings of other hominids, to the taxonomic classification and its relationship with other species of the genus Homo. The absence of cranial remains of adult individuals is a problem to confirm the new species (only 2 of the individuals found in Gran Dolina are adults of about 20 years). Certain juvenile characteristics may be lost in the adults of the species. The most accepted hypothesis, according to its discoverers, is that H. antecessor would be a link between the H. ergaster and the H. heidelbergensis, and at the same time the last common ancestor between humans and Neanderthals. Certain dental and cranial features have suggested that H. ergaster, which lived in Africa more than 1.5 Ma and then migrated to Europe, would be the ancestor of H. antecessor, and this gave rise to H. heidelbergensis, which later gave rise to the Neanderthals. However, there are paleoanthropologists who consider that the Atapuerca remains correspond to a local group of H. erectus or even early H. heidelbergensis, while others believe that it would be a species without descendants, unrelated to the latter.

Chronology of human evolution

The scenario of evolutionary and temporal relationships of H. antecessor could be as follows: the H. ergaster gave rise to H. antecessor in Africa. A million years ago, it spread through the Middle East to Europe, including Atapuerca. In Europe, H. antecessor evolved into H. heidelbergensis, which were the ancestors of the Neanderthals. In Africa, H. antecessor evolved into H. sapiens through an unknown species, though possibly represented by the Bodo and Kabwe skulls. In this scenario, H. heidelbergensis is outside the line leading to modern humans, being a descendant of H. antecessor in Europe. The H. heidelbergensis would require a name change, perhaps to Homo rhodesiensis, the name originally given to the Kabwe skull.

Occupation of Europe

When analyzing the first occupations in Europe, numerous questions arise, of which three stand out: geographic origin of the first settlers from Asia or Africa?, when did it occur?, did it involve large migratory waves or only dispersed and few groups ? Note the chronological gap between the first exit from Africa, 1.8 Ma ago (the H. georgicus belongs to this exit), and the first occupations of Europe much later.

In the prehistory of Europe we find four technical modes of lithic industry, of which we highlight: mode 1 or Olduvayense of boulders, and mode 2 or Acheulean of large flakes and tools. Europe is said to have been colonized by two groups of hominins at different times and of different genetic origin. In the Lower Pleistocene by mode 1 makers, and in the Middle Pleistocene by late Acheulean makers, the H. heidelbergensis. Currently, these two episodes are divided into two phases, one early and one later. A first phase 1.4-1.3 Ma with the lithic industries of edges and cores of Fuente Nueva 3 and Barranco León in Guadix-Baza, Orce and Sima del Elefante in Atapuerca; the second phase about 0.9 Ma with mode 1 in level TD6 of Gran Dolina, associated with H. predecessor; the third phase with large format instruments in the Barranc de La Boella (Tarragona); and the fourth phase 0.6 Ma ago with an evolved Acheulean and the H. heidelbergensis. The possibility of discontinuity between the two great waves, of a genetic continuity between these populations, or of a mixed scenario with possible hybridization between both populations arises. It should be noted that mode 3 or Mousterian would correspond to Neanderthals, while mode 4 of the Upper Paleolithic would correspond to the HSAM.

In the 1980s the UAC candidate for the last common ancestor was H. heidelbergensis, which would have evolved into H. sapiens in Africa and H. neanderthalensis in Europe, 0.4 Ma ago, in the Middle Pleistocene. The refinement of fossil DNA techniques has made it possible to establish the divergence between the two lineages around 0.8 Ma, close to H. predecessor. If the origin of the H. sapiens is in Africa, we must explain how H. antecessor in Iberia. In Africa, remains have been found in Tighennif or Ternifine (Algeria) corresponding to H. erectus mauritanicus, and other fossils of the same age in Daka (Ethiopia) and Buia (Eritrea), but these appear to be descendants of H. ergaster.

The human fossils found in the Sierra de Atapuerca are the oldest and most complete human evidence to investigate who the first Europeans were. There are two main theories about the arrival of H. antecessor to the Iberian Peninsula:

• UAC's hypothesis of origin in Eurasia: a Euro-Asian clay from populations of H. erectus for a spice event 1 Ma. One of the resulting species was installed in the Near East, from which successive waves of immigrants had to be broken during the Lower and Middle Pleistocene in different directions, to the east and to the west provided that biogeographic and paleoambiental conditions allowed it. TD6 hominins could then represent one of those successive waves, coming through the Levantine Corridor. A possible hybridization between residents and those arriving in a new wave could also occur. Other waves could have reached the eastern end of Eurasia, which would explain the shared traits between the TD6 fossils and the Chinese fossils of Nanking, Yunxian and Zhoukudian. This hypothesis implies the arrival in Europe from the east, that the evolutionary courses in Africa and Eurasia could have been relatively independent, and that some populations of this Eurasian UAC will return to Africa to evolve towards modern humans.
• Hypothesis of the arrival of H. predecessor to Europe from North Africa, through the Strait of Gibraltar or the Sea of Alboran. The reasons for dispersal to Iberia could be the high aridity of North Africa. In addition, in Tighennif (Algeria) and in the Victoria cave of Cartagena there are remains of the Cercopiteco cabon Theropithecus oswaldi, from 0.9 to 1 Ma. On the other hand, remnants of the typical Oldowan industry in North Africa were found in Barranco León (Orce, Granada) of 1,25 and 1.4 Ma, along with African fauna. All this supports the viability of diversity between the two shores, and the use of these maritime routes by humans to reach from North Africa to Iberia.

Conclusions

The discovery of new fossils in Africa and Europe in the last two decades, the improvement of the methods of dating the sites, the study of the climate of the past, the progress in the DNA investigations of the fossils and more precise studies of the human remains of the Gran Dolina, have led the Atapuerca team to issue a new hypothesis about the first European settlements: approximately 1 million years ago, an emerging population arose within the framework of human evolution, which became the "mother" of several species that inhabited Africa and Eurasia from the end of the Lower Pleistocene to the present. For biogeographical and climatic reasons, this "source" population could be located in the Levantine Corridor of southwest Asia, which connects Africa with Eurasia.

The colonization of Europe could be carried out by successive migrations from this area, from this original population that followed its own evolution in this area, changing its genotype by mutation and natural selection. During the ice ages in the northern hemisphere, this The area turned green and became a favorable region for the formation of new species. It is possible that one of the first derived species was H. antecessor, because its morphology shows the oldest known “human face” and because of certain characters that would later inherit the H. neanderthalensis.

The population pattern of the paleodemes would consist of frequent processes of expansion and contraction with substitutions and local extinctions of groups during the glacial periods. Climate and geographic barriers would contribute to the occasional isolation of populations. In addition, these dispersals could favor genetic drift, random allelic variations in their offspring, the founder effect, local adaptations, and finally, allopatric speciation. Populations with common and recent origin in the same territory could interbreed given their genetic similarities.

There is the possibility of an evolutionary scenario for Europe with populations from the Lower Pleistocene like those of TD6, replaced or genetically absorbed by new populations arriving in Europe, such as those from Sima de los Huesos. This hypothesis has been reinforced by molecular analyzes of the Neanderthal and Denisovan genomes, which outline scenarios where primitive lineages could have coexisted, or interbred genetically with hominids of more recent origin. the H. antecessor was not the species that gave rise to the neanderthal and H. sapiens present, it is evident that it was related to its origin.

It should be noted that other authors consider that the remains of TD6 would correspond to H. erectus for having an almost identical median facial morphology between the two, and considering that its arrival in Europe must be seen through the Strait of Gibraltar or the Alboran Sea.

Taxonomic issues are always controversial within the scientific community. Paleogenetic studies must be refined to reduce the time range of the divergence between the Neanderthals lineages and modern humans, knowing that both lineages belong to the same clade as H. antecessor. New discoveries of the future and comparative studies between different species should be able to shed enough light on current questions over time.