中国科学院南京地质古生物研究所机构知识库

The terminal Neoproterozoic (Ediacaran) Dengying Formation in southern Shaanxi, China, hosts two types of conical fossils: one is the so-called Conotubus, found in siliciclastic rocks in the lower and middle part of the Gaojiashan Member; the other is the renowned Cloudina in carbonate rocks of the upper Gaojiashan Member and succeeding Beiwan Member. Conotublis are conical and gently curved tubular fossils, with a variable rate of expansion. They are built of multiple thin, steep, eccentrically nested funnels set one within the next. A detailed comparison of the two conical fossils suggests that the organic tubes of Conotubus may be the precursor of the mineralized Cloudina tubes; this inference is consistent with their similarities in both wall structure and life style. Our research thus suggests that the organic skeleton preceded the rise of the mineralized skeleton in Cloudina-like fossils. Sophisticated hypotheses have been advocated, some linking the skeletal genesis to increasing levels of Ca2+ in the seas. others to the enlargement of body sizes of animals. Yet our findings have supported the 'arms race' hypothesis: skeletons evolved primarily through selective predation pressure. Copyright (c) 2007 John Wiley & Sons, Ltd.