|The "Boy of Gran Dolina" fossils ATD6-15 (frontal bone) and ATD6-69 (maxilla) at the Museo Arqueológico Nacional de España|
Bermúdez de Castro et al., 1997
Homo antecessor is an archaic human species of the Lower Paleolithic, known to have been present in Spain, and possibly England and France, between about 1.2 million and 0.8 million years ago (Mya). It was described in 1997 by Eudald Carbonell, Juan Luis Arsuaga and José María Bermúdez de Castro, who based on its "unique mix of modern and primitive traits" classified it as a previously unknown archaic human species.
The fossils associated with Homo antecessor represent one of the oldest direct fossil record of the presence of Homo in Europe. The species name antecessor proposed in 1997 is a Latin word meaning "predecessor", or "vanguard, scout, pioneer". Authors who do not accept H. antecessor as a separate species consider the fossils in question an early form of H. heidelbergensis or as a European variety of H. erectus.
The Sierra de Atapuerca had long been known to be abundant in fossil remains. The Gran Dolina ("large sinkhole") was first explored for fossils by archaeologist Francisco Jordá Cerdá in a short field trip to the region in 1966, who recovered a few animal fossils and stone tools. He lacked the resources and manpower to continue any further. In 1976, Spanish palaeontologist Trinidad Torres investigated the Gran Dolina for bear fossils (he recovered Ursus remains), but was advised by the Edelweiss Speleological Team to continue at the nearby Sima de los Huesos ("bone pit"). In addition to a wealth of bear fossils, he also recovered archaic human fossils, which prompted a massive exploration of the Sierra de Atapuerca, at first headed by Spanish palaeontologist Emiliano Aguirre but quickly taken over by José María Bermúdez de Castro, Eudald Carbonell, and Juan Luis Arsuaga. They restarted excavation of the Gran Dolina in 1992, and found human remains 2 years later, which in 1997 they formally described as a new species, Homo antecessor.
The 25 m (82 ft) of Pleistocene sediments at Gran Dolina are divided into 11 units, TD1 to TD11 ("trinchera dolina" or "sinkhole trench"). H. antecessor was recovered from TD6, which has consequently become the most well-researched layer of the site. The first field season 1994–1996 excavated a small test pit (to see if the unit warrants further investigation) measuring 6 m2 (65 sq ft). This recovered nearly 100 specimens, the best preserved ATD6-15 and ATD6-69, a frontal bone and a maxilla (upper jawbone) of a 10 year old boy nicknamed the "Gran Dolina Boy" (el chico de la Gran Dolina). In subsequent field seasons from 2003 to 2007, a 13 m2 (140 sq ft) triangular section was excavated, yielding about 70 more specimens. In 2007, a molar was recovered from the nearby Sima del Elefante ("elephant pit"). It belonged to a 20–25 year old individual. In 2008, an additional mandible fragment, stone flakes, and evidence of butchery were discovered. In 2014, 50 footprints dating to between 1.2 million and 800,000 years ago were discovered in Happisburgh, England, which could potentially be attributed to an H. antecessor group given it is the only species identified during that time in Western Europe.
Age and taphonomy
The 2003 to 2007 excavations revealed a much more intricate stratigraphy than previously thought, and TD6 was divided into 3 sub-units spanning 13 layers and 9 sedimentary facies. Human presence is recorded in sub-units 1 and 2 and in facies A, D1, and F. Randomly orientated scattered bones were deposited in Facies D1 of layer TD6.2.2 (TD6 sub-unit 2, layer 2) and Facies F of layers TD6.2.2 and TD6.2.3, but in Facies D they seem to have been conspicuously clumped into the northwest area. This might indicate they were dragged into the cave via a debris flow. As for Facies F, which contains the most human remains, may have been deposited by a floodplain-related geological process inflowing from the main entrance to the northwest, as well as a stronger debris flow from another entrance to the south. Fluvially deposited fossils (dragged in by water) were recovered from Facies A in layers TD6.2.2, TD6.2.1 and TD6.1.2, indicated by limestone gravel within the size range of the remains. Thus, H. antecessor may not have inhabited the cave, but was active nearby. Only 5.6% of the fossils bear any evidence of weathering from open air, roots, and soil, which could mean they were dragged into the cave relatively soon after death.
In 1999, the Gran Dolina boy was dated to 859–782,000 years ago. In 2008, the Sima del Elefanta was dated to dating to 1.2–1.1 million years ago. In 2013, TD6 was dated to about 780,000 years ago. In 2014, the Gran Dolina was dated at 900,000 years old in 2014. n 2018, direct ESR dating of ATD6-92 resulted in an age of 949 to 624 thousand years ago, further restricted by magnetostratigraphic data from TD6 to 949 to 772 thousand years ago. Until 2013 with the discovery of the 1.4 Ma infant tooth from Barranco León, Orce, Spain, these were the oldest human fossils known from Europe, though human activity on the continent stretches back as early as 1.6 mya in Eastern Europe and Spain indicated by stone tools.
H. antecessor has been proposed as a chronospecies intermediate between H. erectus (c. 1.9–1.4 Mya) and H. heidelbergensis (c. 0.8–0.3 Mya). While H. heidelbergensis is widely accepted as the immediate predecessor of H. neanderthalensis, and possibly H. sapiens, the derivation of H. heidelbergensis from H. antecessor is debatable. H. antecessor's discoverers suggested H. antecessor as a derivation of African H. erectus (H. ergaster) which would have migrated to the Iberian Peninsula at some point before 1.2 Mya, and developed into H. heidelbergensis by 0.8 Mya, and further into H. neanderthalensis after 0.3 Mya.
In 2009, palaeoanthropologist Richard Klein stated he was skeptical that H. antecessor was ancestral to H. heidelbergensis, interpreting H. antecessor as a "failed attempt to colonize southern Europe". The legitimacy of H. antecessor as a separate species has also been questioned because the fossil record is fragmentary, and especially as no complete skull has been found, with only fourteen fragments and lower jaw bones known. Because of this, it is also proposed that H. antecessor was an early form of H. heidelbergensis, which would extend the range of H. heidelbergensis to 1.2–0.3 Mya. A 2020 analysis by Welker et al. of ancient proteins collected from a tooth of an H. antecessor specimen indicated that H. antecessor belonged to a "sister lineage" related to the ancestor of modern humans, Neanderthals, and Denisovans, but was not itself their ancestor, corroborating earlier opinions that H. heidelbergensis was not derived from H. antecessor.
The facial anatomy of the 10 to 11.5 year old specimen ATD6-69 is strikingly similar to modern humans (as well as East Asian Middle Pleistocene archaic humans) as opposed to West Eurasian or African Middle Pleistocene archaic humans or Neanderthals. Though, African Middle Pleistocene humans (the direct ancestors of modern humans) would later evolve this condition. The most notable traits are a completely flat face and a curved zygomaticoalveolar crest (on the cheek). Assuming these features would not disappear with maturity, H. antecessor suggests the modern human face evolved and disappeared multiple times in the past, which is not unlikely as facial anatomy is strongly influenced by diet and thus the environment. The mandible (lower jaw) is quite gracile unlike most other archaic humans. It exhibits several archaic features, but the shape of the mandibular notch is modern humanlike, and the alveolar part (adjacent to the teeth) is completely vertical. Like many Neanderthals, the medial pterygoid tubercle is large. Unlike most Neanderthals, there is no retromolar space (a large gap between the last molar and the end of the mandible).
The upper incisors are shovel-shaped (the tongue side is distinctly convex), characteristic of other Eurasian human populations. The canines bear the cingulum (towards the base) and the essential ridge (towards the midline) like derived species, but retain the cuspules (small bumps) near the tip and bordering incisor. The upper premolar crowns are rather derived, being nearly symmetrical and bearing a lingual cusp (on the tongue side), and a cingulum and longitudinal grooves on the cheekward side. The upper molars feature several traits typically seen in Neanderthals. The mandibular teeth, on the other hand, are quite archaic. The P3 (the first lower premolar) crowns are strongly asymmetrical and have complex tooth root systems. P3 is smaller than P4 like more derived species, but like other early Homo, M1 (the first lower molar) is smaller than M2 and the cusps of the molar crowns make a Y shape.
The parietal bone (comprising the back of the top of the skull) is flattened, each exhibiting a "tent-like" posterior profile (when looking at the individual from the back), much like more archaic African H. ergaster and Asian H. erectus. Like H. ergaster, the temporal styloid process just below the ear is fused to the base of the skull. The brow ridge is prominent. The upper margin of the squamous part of temporal bone (on the side of the skull) is convex, like in more derived species.
Based on teeth eruption pattern, H. antecessor had the same development stages as modern humans, though probably at a faster pace.
The notably large adult clavicle specimen ATD6-50, assumed male based on absolute size, was estimated to have stood 162.3–186.8 cm (5 ft 4 in–6 ft 2 in), mean of 174.5 cm (5 ft 9 in), based on the correlation among modern Indian people between clavicle length and stature. An adult radius, ATD6-43, which could be male based on absolute size or female based on gracility, was estimated to have been 172.5 cm (5 ft 8 in) tall based on the average of equations among several modern populations relating radial length to stature. Based on metatarsal (toe bone) length, a male is estimated to have stood 173 cm (5 ft 8 in) and a female 168.9 cm (5 ft 6 in). These are all rather similar values. For comparison, Western European Neanderthal estimates average 165.3 cm (5 ft 5 in), and early European modern humans 178.4 cm (5 ft 10 in). The ankle joint is adapted for handling high stress, which may indicate a heavy, robust body plan, much like Neanderthals.
Two atlases (the first neck vertebra) are known, which is exceptional as this bone rarely ever fossilizes for archaic humans. They are indistinguishable from those of modern humans. For the axis (the second neck vertebra), the angle of the spinous process (jutting out from the vertebra) is about 19°, comparable with Neanderthals and modern humans, diverging from H. ergaster with a low angle of about 8°. The vertebral foramen (which houses the spinal cord) is on the narrow side compared to modern humans. The spine as a whole otherwise aligns with modern humans.
There is one known (and incomplete) clavicle, ATD6-50, which is thick compared to those of modern humans. This may indicate H. antecessor had long and flattish (platycleidic) clavicles like other archaic humans. This would point to a broad chest. The proximal curvature (twisting of the bone on the side nearest the neck) in front-view is on par with that of Neanderthals, but the distal curvature (on the shoulder side) is much more pronounced. The sternum is narrow. The acromion (which extends over the shoulder joint) is small. The shoulder blade is similar to all Homo with a general human body plan, indicating H. antecessor was not as skilled a climber as non-human apes or pre-erectus species, but was capable of efficiently launching projectiles such as stones or spears.
The incomplete radius of the forearm, ATD6-43, was estimated to have measured 257 mm (10.1 in). It is oddly long and straight for an archaic human, which could indicate a high brachial index (radial to humeral length ratio), reminiscent of the proportions seen in early modern humans and many people from tropical populations. This could be explained as retention of the ancestral long-limbed tropical form, as opposed to Neanderthals which evolved shorter limbs. Compared to more recent human species, the cross-section of the radial shaft is rather round and gracile throughout its length. Like archaic humans, the radial neck (near the elbow) is long, giving more leverage to the biceps brachii. Like modern humans and H. heidelbergensis, but unlike Neanderthals and more archaic hominins, the radial tuberosities (a bony knob jutting out just below the radial neck) are anteriorly placed (towards the front side).
Like other archaic humans, the femur features a developed trochanteric fossa and posterior crest. These traits are highly variable among modern human populations. The two known kneecaps, ATD6-22 and ATD6-56, are subrectangular in shape as opposed to the more common subtriangular, though are rather narrow like those of modern humans. They are quite small and thin, falling at the lower end for modern human females. The apex of the kneecap (the area which does not join to another bone) is not well developed, leaving little attachment for the patellar tendon. The medial (towards the midline) and lateral (towards the sides) facets for the knee joint are roughly the same size in ATD6-56 and the medial is larger in ATD6-22, whereas the lateral is commonly larger in modern humans. The lateral facet encroaches onto a straight flat area as opposed to being limited to a defined vastus notch, an infrequent condition among any human species.
The phalanges and metatarsals of the foot are comparable to those of later humans, but the big toe bone is rather robust, which could be related to how H. antecessor was pushing off the ground. The ankle bone is exceptionally long and high as well as the facet where it connects with the leg (the trochlea), which may be related to how H. antecessor transmitted body weight. The long trochlea caused a short neck of the talus. This somewhat converges with the condition exhibited in Neanderthals, which is generally explained as a response to a heavy and robust body, to reduce stress to the articular cartilage in the ankle joint because it would have been subjected to higher stress. This would also have permitted greater flexion.
The Gran Dolina preserved approximately 200 stone tools and 300 animal bones. Stone tools including a stone carved knife were found along with the ancient hominin remains.
The large animal carcasses at Gran Dolina appear to have been carried to the site intact. This indicates that H. antecessor groups dispatched multi-member hunting parties who delayed eating immediately after a successful kill in order to share it with all group members after hauling it back, showing social cooperation, division of labour, and food sharing. A total of 16 species were recorded from Gran Dolina, including the bush-antlered deer, an extinct species of fallow deer, an extinct red deer, an extinct bison, a wild boar, the rhino Stephanorhinus etruscus, the Stenon zebra, a mammoth, the Mosbach wolf, the fox Vulpes praeglacialis, the Gran Dolina bear, the spotted hyena, and a lynx. The most common butchered remains are those of deer. Also, adult and child H. antecessor specimens from Gran Dolina exhibit cut marks, crushing, burning, and other trauma indicative of cannibalism, and are the second-most common remains bearing evidence of butchering. It is unclear if cannibalism was practiced often (ritual cannibalism) or if this was an isolated incident in a dire situation (survival cannibalism).
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