THE ASTRORHIZAE OF FOSSIL STROMATOPOROIDS CLOSELY APPROXIMATE AN ENERGETICALLY OPTIMAL FLUID TRANSPORT-SYSTEM

Direct measurements on 375 million year old stromatoporoid sponges sho w that the astrorhizal canals (excurrent flow channels) have a near-op timal architecture; they are configured such that the energetic costs to construct and operate these fluid transport systems averaged only 2 .54% above those of equivalent Murray's Law systems, the theoretical m inimum. The average cost incurred by the fluid transport system in str omatoporoids was a factor of three closer to the Murray's Law optimum than are vessel networks in the circulatory system of mammals.