Phylogenetic analysis of the metazoan evolutionary tree as a whole, and of trees of component major clades, indicates that marine herbivores, defined here as macrophagous consumers of living multicellular attached marine plants, always occupy terminal positions at several scales of analysis. Nearly all living benthic marine herbivores are derived from microphages, detritivores, or predators, and most have post-Paleozoic origins. The derived nature of herbivory in the sea parallels the evolutionary situation among land animals. Pre-Mesozoic marine benthic ecosystems, characterized by relatively low rates of flow of energy and nutrients, may have relied even more heavily on decomposers for the transfer of carbon from primary producers to animals than do living marine ecosystems in the photic zone.

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