The Times and Climes of Homo erectus

The bullnecked and bullet-headed species Homo erectus was physically primitive enough to be a compelling human ancestor. But once the anatomical descriptions of the hominid, authored by Davidson Black and then Franz Weidenreich, were largely completed, paleoanthropologists (and the public in general, to whom "Peking Man" had become a household name) wanted more details. Like the forthcoming sequel to a novel or the next installment of a serialized movie, the latest research findings from China were awaited with eager anticipation. Many questions surrounding Homo erectus related to their exotic context. Just how old were these fossils? Did erectus live through the cold of the Ice Age? Where had they come from? By drawing on fields outside the traditional realms of physical anthropology and archaeology, we have been able to piece together much of when and under what conditions Homo erectus lived.

Questions about Homo erectus behavior have to be placed in an environmental context first. Did these hominids from the Ice Age live amid snow and ice, adapting like modern-day circumpolar peoples such as the Inuit, or were conditions less extreme? Did they stay in one place—for example, near Longgushan—most of the year, or did they move with the seasons? What sort of shelter and clothing would have been necessary? Most of these pressing questions were not answered in the lifetimes of the first investigators (and some are still not answered) because resolution has had to wait for sophisticated dating techniques and the integration of results from many different subfields of science. Only recently has it been possible to construct a firm contextual story for the Longgushan fossil hominids, and the most basic part of the story is the geological age of the site.

The Times and Climes of Homo erectus 109 The Age(s) of Longgushan

By the early 1930s it had become apparent to the excavators that Locality 1 was a single big cave infilling. Sediments and bones had become incorporated in a more or less continuous process lasting tens or hundreds of thousands of years. Yet there were smaller discrete fossil deposits spread over Dragon Bone Hill that were unconnected with Locality 1. These were surveyed and designated as different "localities" (as distinguished from the "loci" within Locality 1 discussed earlier).

The relative ages of these various localities were bracketed by the species of fossil mammals discovered in them. This way of determining the age of fossil deposits is known as biostratigraphy, and it has been used since the dawn of paleontology. Locality 12, for example, located half a kilometer east of Locality 1, had in its inventory of species a more primitive monkey (Procynocephalus) than the species at Locality 1 (Macaca robusta). It was assigned an early Pleistocene age. On the other hand, the Upper Cave site (also known as Locality 26) yielded a fauna essentially identical to that of northern China today. It was assigned a latest Pleistocene age. In all, there are 45 localities at Dragon Bone Hill that span the time from the recent past back through the entire Pleistocene Epoch, and even into the epoch before, the Pliocene. These localities tell the story of the climatic and biotic evolution of China before and during the Ice Ages.

Locality 15 is the oldest known locality at Longgushan. It is unique among the localities in many ways. First of all, its sediments are river-laid sands, silts, and gravels. And the fossils from Locality 15 are virtually entirely those of freshwater fish. Locality 15 records a time when the land surface at Longgushan was lower relative to the Zhoukou or Ba'er River, because water inundated the cave when the river was high and during floods. Fish were swept into the cave and died where they were trapped. As the water evaporated, their skeletons were entombed in the enclosing river mud that eventually turned to stone and fossilized them. Locality 15 is dated to the Pliocene Epoch because the species of fish found there are the same as those found at other Asian Pliocene sites. The site has never been dated by absolute dating methods (techniques that can give an age in years) so its date is termed "relative." We estimate that Locality 15 is between three and five million years old.

Sometime after Locality 15 was deposited, Locality 12 formed. Many years are missing between these two localities because Locality 12 is early Pleistocene, dated by relative dating to less than two million years ago. During this span of time the Zhoukou River cut down into its valley, meandering in S-shaped turns as it did so. The bedrock of Longgushan was slowly uplifted, pushed up by crushing forces in the earth's crust and movement

Rivers Book Dragon Bones

The other localities of Dragon Bone Hill. Above: Geological sketch (not to scale) of Dragon Bone Hill localities and sediments by Teilhard de Chardin. Below: View of Dragon Bone Hill from the north. Dragon Bone Hill is, like the rest of the Western Hills, made up predominantly of limestone originally deposited in ancient seas during Ordovician times (ca. 400 million years ago). The much more recent sediments were deposited in these uplifted, tilted, and faulted limestone rocks. The top of Dragon Bone Hill is composed of the oldest of these recent sediments—remnants of a Miocene and Pliocene cave system now almost entirely removed by erosion (1 = "Yellow Sands" with fish fossils; 2 = gravel; 3a = cave flowstone (stalagmite). Locality 12 (3b) was a fissure infilling of this early cave system in which many monkey fossils were found in the " Cynocephalus Gravels." Locality 13 (4) is an early Pleistocene deposit of red clay with many fish fossils, probably representing a lake deposit. Locality 1 (5a, 5b) represents early-middle Pleistocene deposits, which are the only sediments known to preserve Homo erectus fossils. Terrace deposits near the Zhoukou River (5c) may correspond in age to the Locality 1 sediments. Upper Cave (7) with late Pleistocene exposures can be seen adjacent to Locality 1. Locality 3 (6) is a middle Pleistocene deposit with few fossils.

SO 0 100 200 300m

© - © Fossiferous Localities A Upper Cave Site

Fifteen localities were originally established on Dragon Bone Hill. Eleven of these localities can be identified on this map. Only Locality 1 (in bold) preserves hominid remains, but the others provide valuable paleoenvironmental data for the conditions before and after Homo erectus frequented the cave at Locality 1. A total of 45 localities have now been established at Dragon Bone Hill. For views of other localities see previous figure.

along cracks or faults in that crust. The net effect of these geological events was to cause a much drier interior in the developing Longgushan cave. The cave began to be populated by terrestrial animals.

Pierre Teilhard de Chardin first noted the steady uplift of the Zhoukoudian region from the Pliocene to the present.1 This uplift accounted for the major change in the fossil fauna from fish to terrestrial. Teilhard synthesized much of the information about the early Longgushan localities and produced a summary chart.

From the standpoint of our interest in human evolution, the uplift of the Longgushan cave and its trapping of terrestrial animal bones was a good thing. But the fact that the cave was now above the river's floodplain meant that river sediments would no longer come into the cave and cover the bones, fossilizing them. Sediments could now only come to enclose bones when deposited by groundwater seeping through the roof and walls of the cave—as in stalactites and stalagmites (flowstone), by rainwater runoff pouring in through the external openings of the cave, or by sediments blowing in from the outside. The deposits in Longgushan Cave preserve some flowstone, but the predominant type of sediment that fills the cave is breccia (Italian for "broken"), composed of fallen boulders and slabs of bedrock from the roof, cemented by washed-in silt, sand, and loess from the soil surface above.

Teilhard de Chardin, in a remarkable feat of reasoning—considering the data available to him—deduced that the times of deposition at Longgushan would have had to correlate to periods of increased rainfall (and decreased ice), which would have been during periods of relative warmth. The gaps in time between the various localities at Longgushan then were explicable in terms of cycles of sedimentation—sediments and fossils were deposited only during wet and warm periods of the Pleistocene. During periods when water was locked up in glaciers, and rainfall was scarce, there was no sediment washed into the cave. Teilhard correlated the periods of increased sedimentation (and fossil deposition) at Longgushan with the cycle of Pleistocene "interglacials"—the periods in between the glacial periods long known in European and North American geology.

Despite the prescience of Teilhard's inspired geological deductions, the history of sedimentation and therefore the ages of the fossils in the cave remained unproven until methods of absolute dating were applied to the cave. But this sounds much easier than it proved to be in practice. Too old for carbon-14 dating and lacking potassium-rich volcanic rocks that could be dated by the potassium-argon method, the sediments at Longgushan had to await the development and refinement of various absolute-dating methods that have only recently begun to yield consistent results.

Teilhard de Chardin's concept of past climate in northern China. Sedimentation increased during warm periods ("interglacials"), with increased rainfall and melting glaciers, numbered I through IV. Glacial periods were times of decreased sedimentation, lettered A through G. Teilhard placed Zhoukoudian Locality 1 ("C.k.t.") in Interglacial Period III (his Cycle III), a warm and wet period. Superimposed on this cyclic climatic change was geological uplift of the sediments as well as a general trend toward colder conditions over time. Modern research has modified and refined this framework but much of Teilhard's model is still valid.

Teilhard de Chardin's concept of past climate in northern China. Sedimentation increased during warm periods ("interglacials"), with increased rainfall and melting glaciers, numbered I through IV. Glacial periods were times of decreased sedimentation, lettered A through G. Teilhard placed Zhoukoudian Locality 1 ("C.k.t.") in Interglacial Period III (his Cycle III), a warm and wet period. Superimposed on this cyclic climatic change was geological uplift of the sediments as well as a general trend toward colder conditions over time. Modern research has modified and refined this framework but much of Teilhard's model is still valid.

Was this article helpful?

0 0
The Power Of Charisma

The Power Of Charisma

You knowthere's something about you I like. I can't put my finger on it and it's not just the fact that you will download this ebook but there's something about you that makes you attractive.

Get My Free Ebook


Post a comment