Anadara Mound Building – a Puzzling Period

Australia: The Land Where Time Began

Anadara Mound Building – a Puzzling Period

The construction of marine shell mounds over a limited period in the Late Holocene is another example of a changing economy. Along more than 3,000 km of the tropical northern coastline, from the Kimberley region to Cape York Peninsula, these mounds have been constructed. These mounds, which are conical piles of steep ridges of shell often also contain sediment, artefacts, animal bones and ash in small amounts. It was proposed (Tim Stone, 1989) that they were built by generations of scrub fowl building nests rather than by humans, but archaeological discussions concentrated on mounds that were built by humans (Baily, 1991, 1994; Mitchell, 1993; Burns, 1994). The volumes of shell mounds range from less than 1 m³ to several hundred cubic metres; the largest are nearly 100 m in length and more than 10 m high. It has been estimated that the big mounds contain more than 10,000 tons of shell, which came from 10 million molluscs (Bailey, 1994, 1999). Often mounds have been found in clusters, which demonstrated that huge amounts of shell had been discarded on a single location. These mounds are referred to as ‘Anadara mounds’.

Anadara mounds were formed at times in the past when environmental conditions differed from those of the present. They are usually found away from the present day coast, the distances inland varying sometimes hundreds of metres to many kilometres. Mounds were often formed on ancient landforms such as cheniers or laterite slopes or benches, the coast having since prograded, which left them inland (Bailey, 1977, 1994, 1999; Woodroffe et al., 1988; Hiscock & Mowat, 1993; Bailey et al., 1994; Burns, 1999; Faulkner & Clarke, 2004; Hiscock & Faulkner, 2006). It is indicated by the results of radiocarbon analysis of shell and charcoal samples from many sites that Anadara mounds were being formed over a period of 2,000 years; beginning between 3,000-2,500 years ago in Arnhem Land and on Cape York, and the earliest being in the Kimberley. Anadara mounds have not been found that date to more recently than 800-600 BP in most locations; the single known exception if a single mound that has been found on Cape York Peninsula (Bailey, 1994). According to Hiscock it has been interpreted as indicating by this information that a period between 3,000-600 BP, during which coastal foragers harvested large numbers of Anadara and piled the shells up into mounds (Hiscock & Faulkner, 2006). In order for large Anadara beds to form open, silty beaches were needed, conditions which are not now present in the regions where Anadara mounds have been found, evidence that people stopped building these mounds because the environment in which that economy was supported changed.

Archaeologists have been trying to understand economic and social systems that built these mounds. It has been suggested by some that the people piled up shells to gain benefits that became apparent when mounds reached a sufficient size. E.g. if the camps were placed on top of high mounds they would be above flood waters and biting insects, and larger mounds provide suitable habitats for fruit-bearing plants which could be harvested when people visited them (Cribb, 1996). These suggested benefits help in understanding why large mounds were valued and used by foragers but Hiscock suggests they are not powerful reasons for building them. Each mound would have taken several hundred years to build, which is a long time to wait before they had a good campsite or food source, and there is also the problem that many mounds didn’t reach the size at which the suggested benefits would be manifested. These suggested benefits were fortuitous results from the building of mounds but not the central reason for piling up shells. Mounds were not constructed in a single visit to the site, rather a series of occupations. The ‘self-selecting’ model was proposed (Bailey, 1999) to explain why the mounds developed, Bailey suggesting that people preferred camping and discarding shells on areas that were slightly raised and already contained shells so they repeatedly came back to the same localities, which would increase the size of the mounds with each visit. It has been suggested by several researchers that the mounds may have had symbolic significance to the people who built them (Morrison, 2003; Bourke, 2005), though the nature of those ideologies has not been established.

The question of the role that was played by harvesting and consumption of molluscs in coastal economies is raised by large numbers of Anadara mounds. The initial hypothesis that was proposed (Bailey, 1975, 1983, 1994, 1999) was that small groups of foragers collecting sea foods in a single season each year gradually built up the mounds until after centuries they had reached their large size. According to Hiscock the image of small groups of foragers collecting molluscs was observed in the 20^th century, though in the modern case the Aboriginal people who were observed didn’t build mounds with their discarded shells, which is evidence that there has been a change in the behaviour of coastal foragers since the end of the mound building phase. Also, often hints are provided by radiocarbon chronologies that the mounds were possibly built up by irregular occupation, possibly as ‘pulses’ of occupation, and not as annual seasonal use at low levels (Morrison, 2003). It is suggested by this evidence that it was by rare or unusual activities that the shells accumulated in mounds, and not by everyday behaviour.

According to a different hypothesis the building of mounds resulted from exceptional events in which they accumulated by irregular foraging events of high intensity that were carried out by large groups of people when they took advantage of locally abundant shell beds to support ‘social gatherings’. This was proposed for mounds near Weipa on Cape York Peninsula (Morrison, 2003), then was adopted by researchers working in other parts of the northern coast (Bourke, 2005). The intermittent accumulation of some mounds can be explained by this hypothesis, as well as variation in size and locations of sites, though it also draws on lifestyles that have been recorded in the early 20^th century, which implies that there was no economic or social change when the building of mounds ceased.

Economic activities on the northern coast 1,000 years ago differed from those that have been observed historically. As a result of Morrison’s model of mounds being on accumulated at times of rare ceremonial gatherings drawing on details of historic land use, archaeologists were encouraged to think that throughout the Late Holocene the economy and social life of Aboriginal people was the same as during historic times. According to Hiscock this idea is not supported by archaeological data.

According to a 3^rd hypothesis coastal foragers who built mounds of Anadara shells had economic patters that differed from those observed in the 20^th century, with groups of medium size exploiting shell beds regularly and intensively. The shells excavated from mounds are not consistent with interpretations that shells were collected at low levels continuously or harvested at rare events at high intensity. The evidence indicates that the harvesting of Anadara beds was more constant and intensive and that groups were more sedentary than those observed in the recent past.

A study of the harvesting of molluscs during the mound building phase (Faulkner, 2006) was presented by Patrick Faulkner, the excavator of Anadara mounds at Grindall Bay, eastern Arnhem Land, which had accumulated between 3,000 and 600 BP. No mounds are known of dating to later than 1,000 BP until 600 BP, and it is possible the area may have been abandoned for several hundred years, then there was a brief, final period of mound building 600 BP. A consistent size reduction of Anadara shells was observed over a prolonged period ending at 1,000 BP. As molluscs age they grow larger and the shell length decline indicates that coastal foragers were collecting younger animals over time.

Faulkner argued that if foragers were collecting the biggest molluscs available this trend showed that over time there was a change in the age-structure of the Anadara population; it was rare to find older individuals of Anadara in the shell beds by 1,500 BP. He hypothesised that in the later middens large numbers of juvenile, as well as the reduced age of adults, indicated that exploitation of the Anadara beds was so intensive that it often matched or exceeded the reproductive capacity of the Anadara in Grindall Bay. So many adults and older juveniles were removed by harvesting that very few individuals grew to be old and large. To have this effect on mollusc population suggests that large numbers of people probably harvested shell every year.

Intensive human harvesting may have contributed to local collapse of mollusc beds once removal of excessive numbers of adults prevented maintenance of the population, though there may have been other factors contributing to the temporary consumption of Anadara about 1,000 BP. A partial recovery of the source following a period of minimum human exploitation is reflected in the short-lived phase of Anadara mound building at about 600 BP. The foraging for molluscs was focused, at a level that was more intense and structurally different than it was in the historic period, according to Faulkner’s interpretation of the building of shell mounds in the Grindall Bay area. It was suggested by Faulkner that the pattern seen in the Grindall Bay was widespread, though it is not clear whether economic systems that involved mound building were identical in all regions. An adjustment of coastal foragers to changing conditions during the Holocene is illustrated by economies the of Anadara mound builders.

Another reconstruction of the economies of coastal foragers on the Australian north coast occurred following the cessation of the Anadara mound building. Bruce Veitch discussed this (Veitch, 1999), suggesting exploitation of Anadara granosa provided coastal foragers with large amounts of food, and reduced variations in the food supply, which allowed them to have higher densities. Diversification of diet and alterations in the dispersion and mobility of foragers occupying coastal territories followed the end of the large-scale, intensive Anadara harvesting period 600 years ago.

The environmental conditions that allowed a large biomass of Anadara that were easily harvested lasted for a limited time. Anadara disappeared completely from much of the northern coastline in the last 1,000 years, and at present is found at very low densities and only in rare beds. Between 800 and 600 years ago there were many regions where evolution of the landscape changed from shallow embayments and open beaches with large expanses of mud flats that contained massive beds of Anadara to coasts rich in mangroves and mud flats where there were no abundant Anadara. As a result reorganisation of economy and land use resulted: economies that had focused on molluscan resources switched to ones that exploited diverse sets of terrestrial and aquatic resources that were available in the wetland areas, as well as seashores. Associated with these economic shifts were social and ideological shifts, and in response to differences in the rate at which Anadara diminished and the availability of alternative opportunities for foraging.

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