|
Jose Antonio Gamez Vintaned, Universidad de Zaragoza (Spain)
Andrey Yu. Zhuravlev, Universidad de Zaragoza (Spain)
Eladio Linan, Universidad de Zaragoza (Spain)
Aleksandr B. Fedorov, Siberian Scientific-Researching Institute of Geology, Geophysics and Mineral Resources (Russian Federation)
|
|
Several paradigms replaced each other during the second half of the last century, from a complete refutation of any metazoan occurrence in the terminal Neoproterozoic through an acceptance of soft-bodied multicellular animals (vendobionts) to recognition of even skeletal metazoans. However, the current paradigm accepts the presence in the terminal Neoproterozoic (Ediacaran) of weakly biomineralised animals only, hardly above a low metazoan grade of organization, and a later, Early Cambrian, burst of well-skeletonised animals. Indeed, among four genera, which were recognized previously in the Ediacaran strata, namely, Cloudina, Sinotubulites, Namacalathus, and Namapoikia, only the latter is described as a fossil possessing thick skeleton but of a cnidarian or poriferan grade of organization. Here we report new and relatively high diversity assemblages of shelly fossils from the Upper Ediacaran (553-542 Myr ago) carbonates in Spain and Russia (Siberian Platform). In total, 17 skeletal metazoan genera, a third of which are new ones, are recorded. This number is comparable with that known for the basal Lower Cambrian. Despite of problematic affinities, these fossils display well-shaped skeletons with a highly advanced microstructure, well above a cnidarian grade of organization. Also, they built shells of different calcium carbonate minerals and not of a single one as has been recently suggested. Our data thus reveal the terminal Neoproterozoic skeletal bloom that was a real precursor of the Cambrian radiation. Moreover, a co-occurrence of the latest Ediacaran genera with the earliest Cambrian ones in some regions is indicative of a step-by-step replacement of the Ediacaran biota by the Early Cambrian biota rather than of a severe mass extinction of Ediacaran faunas, as another current paradigm states. If soft-bodied vendobionts were probably restricted to the Ediacaran period, much less noticeable earliest skeletal animals could be the real ancestors of Cambrian species.
|
