- Comparative Anatomy
Multiple early hominin occupational sites dating as far back as 780 thousand years ago (Ka)1 have been identified at the archaeological locality known as Zhoukoudian (formerly Cho K’ou Tien). Zhoukoudian is located approximately 42 km southwest of Beijing, China, in an area containing several stratified caves and an abandoned limestone quarry. Since the early 1900s, vertebrate fossils have been recovered from over 30 Zhoukoudian localities2. Two sites in particular have garnered much attention: Locality 1, where at least 40 Homo erectus individuals3 and numerous stone tools were recovered; and Upper Cave (ZKD UC) where various anatomically modern human fossils have been found. Zhoukoudian is often argued as the earliest evidence for hominin occupation in Eastern Asia, and today continues to receive much scientific attention.
Known locally as Dragon Bone Hill (or Longgu-shan), Zhoukoudian first came to prominence as a fossil site at the turn of the 20th century when a young German naturalist named K.A. Harberer investigated the local custom of ingesting ground bones taken from the Zhoukoudian caves for medicinalpurposes3-5. While collecting samples from a local apothecary, Harberer noticed one of the fossils resembled a human tooth3,4. Harberer returned to the site in 1903 in hopes of finding more remains associated tooth specimen3. Although he failed to find any more hominin material, Harberer’s efforts would prove influential twenty years later3 when Swedish anthropologists Gunnar Andersson began investigations at Zhoukoudian in the early 1920s.
Excavations at Locality 1 conducted between the early 1920s and 1937 by Andersson, Davidson Black, Otto Zdansky, and colleagues produced a large amount of human remains at the site. When Japan invaded China just prior to World War II, work at Zhoukoudian ceased and the fossils were shipped to the United States for safekeeping5. Unfortunately, almost all hominin fossils found prior to the Second Sino-Japanese War (1937-1945) disappeared in December of 1941 and have never been recovered5. Casts made by Franz Weidenreich just before the fossils disappeared remain intact and represent nearly all the information we have today from the early excavations.
Prior to excavations at Locality 1, evidence for hominin occupation outside Africa was restricted to a specimen from Java that dated between 1 Ma and 700 Ka3. In 1926, Black presented arguments for early humans migrations throughout eastern Asia, and by the early 1930s the Zhoukoudian fossils were accepted as early human ancestors by the scientific community10. The H. erectus fossils from Locality 1, known collectively as “Peking Man”, represent early hominin occupation in China nearly contemporaneous with the Java fossil.
Despite the loss of fossil specimens, Locality 1 and Upper Cave remain significant due to their historical preeminence and the world-wide attention that China would later receive in palaeoanthropology. Fossils recovered from Locality 1 were the first H. erectus specimens ever found in China, and they remain one of the largest H. erectus assemblages discovered11,12.
Analyses suggest that Homo erectus occupied Locality 1 sporadically between ~400 Ka and 780 Ka1,6. Another notable Zhoukoudian locality, known as Upper Cave, sits directly above Locality 1 and dates between 12 Ka and 29 Ka5,7-9. Homo sapiens fossils were first discovered in Upper Cave during the 1933 field season, but these specimens were lost at the same time as the H. erectus fossils in 1941. Subsequent excavations from 1949 onwards have yielded many more H. sapiens fossils from Zhoukoudian, and all over China5.
During summer excavations at Locality 1 in 1921 and 1923, Austrian geologist Gunnar Andersson and his assistant Otto Zdansky discovered two hominin teeth dating to the Middle Pleistocene (ca. 781 Ka -126 Ka)5,13,14. A third hominin tooth was discovered in 1927 by Davidson Black, a world renowned anatomist and professor from the nearby Peking Union Medical College who worked closely with Andersson and Zdanksy3. In all, their discoveries consisted of a worn molar, an un-erupted lower adult premolar5described as taurodont (i.e. long and broad)15, and a slightly worn lower left first molar with a wrinkled crown4. Black was convinced more fossils would soon be discovered in the following field seasons, so he assigned the teeth to a contentious new hominin species, Sinanthropus pekinensis (“Peking Chinese man”)3-5. S. pekinensis is known today as Homo erectus.
In December 1929, W.C. Pei , from the Cenozoic Research Laboratory in China, found a nearly complete juvenile skullcap4,5 at Locality 1 that exhibited a low, flat cranial vault, a reclining forehead with a relatively pronounced browridge (i.e., supraorbital torus4,14). Similarities between Pei’s skull cap and the contemporaneous Java H. erectus specimen (discovered in 1891) prompted Chinese scientists to reassign the Zhoukoudian hominins to H. erectus. The presence of H. erectus in both Asia and Southeast Asia localities suggests that the species was widely radiated throughout Asia16.
German anthropologist Franz Weidenreich took over as head of the Zhoukoudian research project in 1935 after Black died of a heart attack while working in the lab3. Prior to World War II, a large amount of cranial and post-cranial material from numerous H. erectus adults and juveniles representing both sexes was recovered from Locality 1, including 5 skull cups, 6 facial fragments, numerous mandibular and dentition remains, and various post-cranial elements4,5. But just after December 7, 1941, nearly hominin material from Zhoukoudian disappeared during shipment to the United States prior to World War II3,4. Fortunately, prior to shipment Weidenreich made meticulous plaster casts and elaborate monographic descriptions of the fossils that have enabled continued analysis today4. The original “Peking Man” casts are currently housed in the American Museum of Natural History in New York.
Post World War II excavation uncovered more H. erectus material between 1949 and 1966: 7 worn teeth, a fragmented female mandible, and humeral and tibial fragments)5,14,17. In fact, analysis confirmed that frontal and occipital fragments discovered in 1966 were from the same individual as a fossilized left temporal fragment first discovered in 1934. These fragments are now designated as Skull V14.
In 1995, an attempt to reconstruct the face of Peking Man was undertaken by Gary Sawyer and Ian Tattersall of the American Museum of Natural History, New York. The newest reconstruction combined bones from several previously unused H. erectus individuals found at Locality 1 to create one, nearly complete cranium12. Unlike the 1930s cast reconstructions by Weidenreich and his assistant Lucille Swan that only used the calotte, mandible and maxilla of female specimens12, Tattersall and Sawyer utilized previously disregarded male specimens to reconstruct a nearly complete skull11,12. Based on the newest reconstruction, the estimated mean endocranial capacity of the Zhoukoudian individuals is 1,043 cc12. The Tattersall/Sawyer reconstruction represents Peking Man as having a large protruding supraorbital torus, slight sagittal keeling, some subnasal prognathism, a sharply angled occipital with a pronounced transverse occipital torus, and flat, thick, rectangular parietals11,12. Interestingly, Peking Man exhibits relatively robust facial morphology (e.g., thick, shelf-like supraorbital torus; relatively wide nasal aperture; relatively large mandible) in an otherwise relatively small face4,5,11. In a pattern similar to modern humans, the Zhoukoudian H. erectus fossils exhibit relatively reduced maxillary first premolars that remain slightly larger than the maxillary second premolars (P2), and the molars decrease in size distally17. The new Peking Man reconstruction features traits more homologous with other H. erectus specimens found at other sites, although Tattersall and Sawyer warn that the new cranium is not intended to server as a reference for H. erectus character states11.
Date estimates of the Zhoukoudian specimens remains problematic. Most analyses suggest that the Zhoukoudian specimens appear relatively late in the Asian H. erectus sequence, with a suggested date of about 780 Ka to 400 Ka1,4. Debates continue, however, as to exactly when hominin occupied Zhoukoudian. Past arguments pointed to altered chemical composition of sediments resulting from geologic compaction16. However, sediments from Layer 3 at Locality 1, the locus of Skull V, was recently analyzed using uranium-series dating, and secured a date of at least 400 Ka16. These results corroborate findings from nearby sites that indicate H. erectus was not present in China after 400 Ka16.
Upper Cave (Locality 4) is located at Zhoukoudian just above the older Locality 1 site, and has produced some of the most important Homo sapiens fossils found in northern China5 Various fragmented remains - cranial, mandibular, post crania, and isolated teeth4 – have been found at the site, including a tarsal bone that has been dated between 10 Ka and 34 Ka4,5. The cranial and postcranial remains from Upper Cave represent at least 8 individuals and include the nearly complete skulls of an adult male known as Skull 101, a young adult female known as Skull 102, and a middle-aged female known as Skull 1035.
The crania from Upper Cave are all indicative of modern human cranial morphology, but many researches have often noted variation between the specimens7,8. Skull 101, the nearly complete adult male cranium and mandible, exhibits a robust mastoid process and external occipital protuberance, and severely worn teeth5. The female Skulls 102 and 103 are relatively smaller and less robust than Skull 1015. The three skulls appear more morphologically similar to one another than to any other coeval H. sapiens specimens from northern China. Among the characters that the Upper Cave skulls have in common are a relatively more robust brow ridge, relatively wide nasal aperture, orbits that sit lower in the face, and a relatively broad interorbital region5.
Faunal samples collected from various areas of Upper Cave have been analyzed using at least 3 different dating methodologies, and have produced at least three different results that all coincide with an Upper Paleolithic (40-10 Ka) timetable. Radiocarbon tests on material from the human occupation layer resulted in a date of 10,175 +/- 360 years BP, and 18,340 +/- 410 years BP for older layers7. Accelerated mass spectrometry tests on faunal material taken from a different location within the cave than the radiocarbon dated material produced a dates of 13,200 +/- 160 years BP to 33,200 +/- 2000 years BP, with a suggested date of 22,000-27,000 years BP7 for the cultural levels.
The best documented association between Homo erectus and lithic industry in China comes from the rich archaeological record from Locality 1 at Zhoukoudian. In addition, unique ornaments and pedants found at Upper Cave suggest a sophisticated change in the lithic industries at Zhoukoudian between ~700 Ka and ~ 30 Ka4.
Austrian geologist Gunnar Andersson first discovered an exotic white quartz material that was not naturally occurring in the area while shifting through quarry debris. He concluded that the quartz must have been imported by the hominins who occupied the site5,13. Further investigations revealed nearly 100,000 stone artifacts associated with the H. erectus material from Locality 1, including an abundance of quartz lithics retrieved from approximately 40 meters (m) of sediments5,19. In addition, more than 100 intact or chipped boulders were found within the cave, and all consisted of foreign materials such as green sandstone, vein quartz, and quartzite13. The green sandstone most likely originated from the nearby Zhoukou River, but the source for the raw quartz was probably much farther away in the granitic massif either to the northeast or south of Locality 113.
The large number of flakes, debitage, and cores discovered at Locality 1 suggests H. erectus engaged in a small flake industry commonly referred to as the Zhoukoudianian chopper-chopper tool industry5,19. Despite its name, the Locality 1 assemblage lacks any of the handaxes or chopping tools that characterize the Acheulean industry from Africa and Europe during the Lower Paleolithic4,5. While some choppers have been recovered from layers 1-11 (420 Ka -680 Ka) at Locality 1, most of the tools are unifacial (i.e. worked only on one side) unlike the bifacial choppers typical of the western industries4. More than 75% of the material recovered from Locality 1 are scrapers, with the remaining content consisting of mostly points. The Locality 1 seriation does include a few awls recovered from the upper layers (1-5)5 at Locality 1. Some believe Zhoukoudian’s small flake industry may represent one of at least two major Paleolithic traditions in China: small, irregular flake tools associated with scrapers present at Locality 1, versus large flakes and choppers found elsewhere in the country19.
Prior to the late 1990s, Zhoukoudian was often cited as the oldest evidence for the controlled use of fire by early humans13,20. Initial reports suggested that the ratio of burned to unburned macrofaunal bones closely matched those of other confirmed fire sites4, and that the presence of discolored bone fragments (e.g. black, green, pale yellow, or grey) with fine cracks and/or fractures5, recovered from Layers 4 (500 Ka)6 and 10 (670 Ka)6 was direct evidence for the use of fire5,20. The clay matrix surrounding the bone fragments appeared in in vivid shades of red and yellow, prompting suggestions that the discoloration resulted from heating and/or baking of the earth13. In addition, chemical analysis performed in 1930 and 1931 on blackened deer antlers also concluded that the color variation resulted from burning5.
A new round of intense analysis in 1998 on deposits from Layers 4 and 10 determined that there was no evidence of a hearth or in situ burning within the cave20. Indeed, the strongest evidence for any use of fire at Zhoukoudian rested on the presence of charred bones closely associated with quartize lithics recovered from Layer 10, and not from the discolored clay sediments as previously suggested. Therefore, the burned deposits of bone and quartzite may indicate that H. erectus used fire when available through natural occurrences, but there is no conclusive evidence that the hominins artificially ignited and manipulated fire20.
The relatively thin depositional sections representing cultural units (identified in Layers 1-3 in the Upper Room and Layers 4-5 in the Lower Room of Upper Cave)8 indicate rather brief periods of occupation. Upper Cave’s primary cultural level, Layer 4, includes an abundance of flint scrapers, chert flakes, a bone needle, broken and polished deer mandibles, and other quartz tools that fit within the East Asian Paleolithic9. Of particular interest is a set of artifacts that includes 7 perforated white stone beads and teeth, all stained by red hematite. This small assemblage has sometimes been interpreted as a necklace, as it was found near one of the crania in Layer 45,9.
Perforated marine shells identified as Arca were also found in situ at the same locus as the ornaments, beads, and teeth5. Interestingly, the nearest origin for the Arca shell is approximately 200 km from the cave5, although it is unknown if this area was part of the Upper Cave hominins home range5. Whether the adornments were purposefully deposited with the H. erectus remains is uncertain. However, small hematite particles were reportedly found stuck to three Homo sapiens crania (found in Layer 4), that some have interpreted as evidence for deliberate burial practices5,8.
All of Zhoukoudian’s faunal material excavated prior to World War II was lost at the same time as the Homo erectus fossils in 1941. Since then, observations from Zhoukoudian’s prehistoric fauna derive from early detailed monographs and analyses of faunal remains recovered since the 1960’s.
As home to the Homo erectus, the faunal remains at Locality 1 hold particular interest for researchers. This material may help answer questions about the diet and/or hunting behaviors of H. erectus. In all, over 97 Middle Pleistocene mammalian species and 62 avian species have been identified from Locality 15. Two primate species, H. erectus and Macaques has been found in nearly all depositional layers, suggesting that they were not habitat specialists. The mammalian species preserved exhibit a range of environmental preferences, which reinforces the geologic data that indicates warm and cold climatic oscillations during Locality 1’s depositional history (~780 Ka - ~420 Ka21). Overall, Locality 1’s faunal remains demonstrate a general trend toward warm climates adapted species. For example, cold forest dwelling species, such as bears (e.g. Ursus cf. spelaeus), beavers, extinct species of rhinos and a giant horse, hyena, and 1 species of elephant22 are predominate in some of the oldest material (Layer 11 - 8, ~680 Ka and ~640 Ka respectively21), while the number of grassland species (i.e. horse, gerbils, mice, pig, hamster, and voles) decreases in Layers 9 and 85. Though the faunal assemblage derived from Layer 7 (~590 Ka21) shows a continued reduction in cold climate species, the biological material may result from flooding. Fossils skulls within the sandy deposits of Layer 7 are relatively complete and show signs of water abrasion5. By Layer 6 (~570 Ka21), warm species typical of temperate zones are again predominate. These deposits include beavers, badgers, predatory cats including the panther and saber-toothed cat, deer, gazelles, rhinos, hamsters, sheep, mice and wolves5. However, cooler climate species return in Layer 5, which is also dominated by carnivores such as bears, predatory cats, fox, hyenas, voles, weasels and wolves5. This trend reverses in Layer 4, where cold climate species are again rare and a large number of warm grassland species are present, including rats (Rattus rattus), sheep, 2 species of shrews, 2 species of voles, rhinos, and horses5. Bats are also present, which indicates a rich vegetation capable of supporting either the insect or fruit resources bat’s prefer. Combined with the geologic and floral evidence, the faunal deposits support inferences that ~500 Ka appears to have been one of the warmest periods at Locality 15,21,22. Layers 1 – 3 appear similar to Layer 6, with predominately warm habitat species typical of temperate zones: badgers, bats, deer, hamsters, hedgehogs, horses, hyenas, and rhinos. Predatory cats, such as the saber-toothed cat is also present, but disappears from toward the youngest layers5.
The remains of the extinct rhino (Dicerorhinus choukoutienensis), an extinct horse Equus sanmeniensis, and many forms of large deer are frequently found throughout Locality 1’s layers5. In fact, most of the herbivores remains consists of these large deer, including over 2000 individuals of the species Megaloceros pachyosteus, an extinct deer with long, curved antlers, and 200 individuals of the species Pseudaxis grayi, and 30 individuals of the deer Moschus moschiferus pekinensis5. Bovids are also present, such as the buffalo-like Bubalus teihardi that is represented by more than 80 individuals5.
Whether or not these animals were part of the diet for the Locality 1 hominins remains ambiguous. With the exception of Layer 7, most faunal material was found broken into smaller pieces, as expected of material consumed by predators. Indeed, coprolites found at the site offer evidence that carnivores were a frequent occurrence at Locality 15. Early reports5 suggested that carnivore material rapidly decreases when H. erectus remains are present5,13, which might indicate carnivores, such as hyenas, were not prey for H. erectus but rather competed with the hominins for food and shelter5. However, there is no consensus as to how much of the faunal deposits were accrued by hominins. In addition, some scientists argue that there is no definitive association between faunal remains, stone tools, and H. erectus found at Locality 122. Some of the same arguments propose that the faunal remains show no sign of tool use, but rather exhibit marking consistent with carnivore activity18,22. Based on these arguments, it may be possible that H. erectus was not an active hunter22.
Although the some activities of H. erectus at Locality 1 are disputed, the occupation of Locliaty 1 by H. erectus is not. There is, however, building consensus that the H. erectus assemblage may result from carnivorous activity. Recent analyses found that the condition and distribution of the H. erectus fossils appears very similar to material typical of a hyena den18. Hominin remains were found in close association to hyena coprolites, around the edges of the cave, or even in areas of the cave that would not receive natural sunlight22. In addition, the rarity of faciomaxillary and basicanial material is also a hallmark of carnivore consumption18,22. A study conducted in 2000 also identified gnaw and bite marks on almost all known H. erectus fossils18. On at least 3 femurs from the Localiy 1 H. erectus assemblage, puncture marks have been interpreted as bite marks and striations have been interpreted as etchings resulting from stomach acid. According to this analysis, the bones were chewed, ingested, and regurgitated by hyenas18. In addition, the scattered condition of the fragmentary remains was done prior to deposition, which indicates that carnivores processed the bones before sedimentation. One hyaenid specimens found at the site, Pachycrocuta brevirostris, is reportedly one of the largest and strongest carnivore species to inhabit the cave and was probably powerful enough to hunt and/or scavenge hominin remains18. Thus, debates continue regarding the hominins fossils taphonomy.
At Upper Cave, the association between Homo sapiens and the faunal deposits is far less problematic than at Locality 1. The presence of modified bone material, namely perforated non-hominin teeth and modified non-hominin bone material including a bone needle, indicates that Homo sapiens was an active participant in the faunal accumulation of Upper cave.
Of the 49 different mammalian species found throughout Upper Cave despotitional layers9,23, including H. sapiens, nearly every species represents a tropical environment5. Small rodents, including squirrels, voles, hamsters, rats, gerbils, zokors, weasels, and porcupines were among the assemblage5,9. Rabbits and hares are also present, as well as 3 bat species and insectivores such as the hedgehog and mole. Among the large mammals are badgers, sheep, cattle, horse, rhinos, elephants, and several genera of the even-toes ungulages, such as the Sika deer (Cervus Nippon), and a species of the chinese water deer (Hydropotes). Bear material was also found in Upper Cave deposits, including Ursus arctos and the extinct cave bear, Ursus spelaeus. Numerous predatory cats and dogs were also identified, such as fox species, a grey wold (Canis lupus), the raccoon dog known as Nyctereutus procyonoids, and hyenas. Among the large cats were lynx, panthers, and the cheetah.
The uplifted mountains of Zhoukoudian are along the western edge the border zone between the northern coniferous belt and the tree barren grassland plains of the temperate steppe. At the beginning of the Middle Pleistocene, Zhoukoudian was covered in a mix of grasslands and woodlands21. The surrounding hills were covered with rich vegetation (i.e. spruce and pine trees) and animals (i.e. deer and birds) typical of a temperate climates5.
However, in its northeastern position on the continent, Zhoukoudian is highly susceptible to climatic fluctuations caused by the Asian winter monsoons. Likewise, the sedimentary records at Zhoukoudian suggest oscillating warm and cold depositional conditions6 over the extended period of Homo erectus occupation (i.e., between ~780 Ka and 400 Ka). For example, the faunal records indicates a gradual warming period between 670 Ka and 640 Ka, when the ratio of species adapted for warm climates gradually increases over that of species endemic of cooler habitats. This was followed by a cold stage, as indicated by the decrease in abundance of temperate adapted species such as the horse, the Sika deer, and warm season grasses5,6,21. By 500 Ka, the climate had reversed once more and Zhoukoudian experienced one of its warmest periods, though it appears to have ended by 470 Ka.
The Zhoukoudian fossils represent the youngest known Chineses H. erectus specimens21, therefore the climatic conditions at 400 Ka are of particular interest. The depositional record at Zhoukoudian also notes a cold stage at 400 Ka, in which the sediments were deposited under frost conditions6. Carbon and oxygen isotopic analysis supports these findings, and suggests an intensification of the winter monsoon between 520 Ka and 410 Ka that resulted in a shorted growing season and the loss of large game animals21. In fact, the strength of the monsoon appears to correlate with global interglacial and glacial periods, in which the monsoon strengthens during glacial periods21. As the strong monsoon at 400 Ka coincides with the last known H. erectus appearance at Zhoukoudian, it may be that the occupation and migration patterns of the hominins were influenced by the increasingly cold and less productive environment.
By the Late Pleistocene, prey animals and carnivores endemic to temperate or tropical environments had to returned to Zhoukoudian. Within Upper Cave, the processed remains of deer, including those of the tropical adapted sika deer, are found within the sedimentary record. Between 12 Ka and 30 Ka, the Homo sapiens that occupied Zhoukoudian were enjoying a warm, productive climate5,7-9.
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