from a model centered on the Central Plain to a model of distinctive regional cultures whose development was stimulated by interaction between regions, a situation he called the "Chinese interaction sphere". Also in the 1980s, Yan Wenming proposed the term "Longshan era" to encompass cultures of the late Neolithic (3rd millennium BC) across the area, though he assigned the Central Plain a leading role. Agriculture The most important crop was foxtail millet, but traces of broomcorn millet, rice and wheat have also been found. Rice grains have been found in Shandong and southern Henan, and a small rice field has been found on the Liaodong peninsula. Specialized tools for digging, harvesting and grinding grain have been recovered. The most common source of meat was the pig. Sheep and goats were apparently domesticated in the Loess Plateau area in the 4th millennium BC, found in western Henan by 2800 BC, and then spread across the middle and lower Yellow River area. Dogs were also eaten, particularly in Shandong, though cattle were less important. Small-scale production of silk by raising and domesticating the silkworm in early sericulture was also known. Ritual Remains have been found in Shaanxi and southern Henan of scapulae of cattle, pigs, sheep and deer that were heated as a form of divination. Evidence of human sacrifice becomes more common in Shaanxi and the Central Plain in the late Longshan period. Early period Excavations in the 1950s in Shanxian, western Henan, identified a Miaodigou II phase (3000 to 2600 BC) transitional between the preceding Yangshao culture and the later Henan Longshan. A minority of archaeologists have suggested that this phase, which is contemporaneous with the late Dawenkou culture in Shandong, should instead be assigned to the Yangshao culture, but most describe it as the early phase of the Henan Longshan. Some scholars argue that the late Dawenkou culture should be considered the early phase of the Shandong Longshan culture. Miaodigou II sites are found in central and western Henan, southern Shanxi and the Wei River valley in Shaanxi. The tools and pottery found at these sites were significantly improved from those of the preceding Yangshao culture. Agriculture was intensified, and the consumption of domesticated animals (pigs, dogs, sheep and cattle) greatly increased. Similarities in ceramic styles of central Henan Miaodigou II with the late Dawenkou culture to the east and the late Qujialing culture to the south suggest trade