It is no surprise that not all environments are exploited. Of 92 possible modes of life — combinations of feeding style, tiering and motility — no more than a dozen are occupied by the end of the Ediacaran. Just four are represented in the Avalon assemblage. The lack of large-scale predation and vertical burrowing are perhaps the most significant factors limiting the ecological diversity; the emergence of these during the early Cambrian allowed the number of lifestyles occupied to rise to 30.