The garden of Ediacara: Discovering the first complex life by Mark A. S. McMenamin

N o paleontological subject comes close to stimulating the public's interest like dinosaurs, but the origin of animals is probably a solid second. As is well known, representatives of nearly all of the animal phyla (e.g., arthropods, molluscs, echino-derms) appear at roughly the same moment in geologic time, the beginning of the Cambrian period, about 550 million years ago. Their sudden appearance has been dubbed the " Cambrian Explosion, " and in recent years the apparent abruptness of the event has increased as improved dating has shrunk the duration of the Cambrian. To some, the Cambrian Explosion presents an evolutionary puzzle that is at odds with the neodar-winian paradigm, and to Mark Mc-Menamin, the author of The Garden of Ediacara, the puzzle can only be solved by accepting a progressivist, neovitalist view of evolution. Although not the first to express dissatisfaction with the neodarwinian paradigm, Mc-Menamin does present some unusual arguments and employ some unique strategies in making his point. McMenamin's neovitalist ideas are based on his interpretation of a group of soft-bodied organisms, the Ediacar-ans, that appear in the fossil record of the Precambrian, just before the Cam-brian Explosion, 550–750 million years ago. Although initially discovered in the 1940s at Ediacara, South Australia, the evolutionary importance of these organisms was not widely appreciated until the 1980s. Since then, they have stimulated a lively debate. At the center of this debate is the question of Edi-acaran affinities: Do they represent the ancestors of Cambrian organisms or are they an evolutionary dead end, a " failed experiment " that left no de-scendants? Ediacaran fossils have now been found in Australia, Eurasia, Af-rica, and North America. They are often large, up to one meter long. And they lack any mineralized body parts, normally occurring as impressions in sandstones and siltstones. In the early 1960s, most Ediacarans were placed within modern animal phyla, such as sponges and corals, implying that the diversification of animals had started during the Precambrian and that some of the major animal body plans were already present prior to the Cambrian Explosion. But a less conventional interpretation , that Ediacarans represent an independent branch of " the tree of life, " not directly related to modern animals, has been championed by Adolf Seilacher. In the 1980s, Seilacher suggested that the Ediacarans had an odd air mattress–like construction, and this, together with their unique mode of preservation, led him to …