Complex sentence: They adapted as the region's environment changed, developing the spear for hunting as smaller animals, like deer, became more prevalent, and by about 1500 BC oysters had become an important food resource in the region.
Split into simpler sentences: They adapted as the region's environment changed, developing the spear for hunting as smaller animals, like deer, became more prevalent. By about 1500 BC oysters had become an important food resource in the region.