Complex sentence: They belonged to hunter-gatherers and the size of the vessels may have been limited by a need for portability; as later bowls increase in size, this is taken to be a sign of an increasingly settled pattern of living.
Split into simpler sentences: They belonged to hunter-gatherers and the size of the vessels may have been limited by a need for portability. As later bowls increase in size, this is taken to be a sign of an increasingly settled pattern of living.