FOSSIL ANEMONES FROM THE LOWER CAMBRIAN CHENGJIANG BIOTA

Anemone and anemone-like forms of polypoidal, soft-bodied animals have virtually no fossil record, aside from a few trace fossils. The origin of living and fossil corals is problematic. The evolution of all major groups of corals is postulated to have taken place by the development of calcification in several different anemone and anemone-like groups which acquired the ability to produce skeletons of calcite and/or aragonite.

Here we report from the famous Lower Cambrian Chengjiang lagerstatten of China, 358 virtually complete fossil specimens of soft-bodied anemones. Preserved as a life assemblage compressed on a single bedding plane, they provide a vivid snapshot of life on the Early Cambrian sea floor. Some specimens contain possible mouths and most contain evidence of mesenteries, pedal discs, columns and oral discs. Some oral discs are surrounded by a single row of simple, unbranched tentacles. The morphology of these ancient fossil anemone shows many similarities with living actiniarian anemones. The hexameral symmetry displayed by the tentacles and longitudinal ridges of the column suggest alliances with Paleozoic scleractiniamorphs, and scleractinian corals but not Rugosa, Tabulata or other orders of Paleozoic corals.

The fossil anemones from the Chengjiang biota may be direct or collateral ancestors of calcified corals, and their discovery provides the first clear evidence that soon after the explosive burst of metazoan radiation in the Early Cambrian seas, anemones had evolved. These soft-bodied fossils may have been ancestors to some Paleozoic and Mesozoic corals as well as to some extant actiniarian anemones.