Abstract

Unlike the celebrated Ediacara fossils, those from the roughly coeval localities of the Kuibis Quarzite of Namibia are preserved not as imprints on the sandstone bedding plane, but three-dimensionally, within the rock matrix. The pattern of deformation and the presence of sand in lower parts of the bodies of Ernietta, the most common and typical of those organisms, indicate that their three-dimensional preservation is a result of a density-controlled sinking of sand-filled organic skeletons within hydrated mud layers. Specimens of Ernietta have preserved various stages of migration across the mud beds. Their wall material, as documented by the mode of deformation, was not only flexible, but also elastic, which makes it unlike chitin. The walls thus seem to be proteinaceous, built probably of a collagenous fabric. The Ernietta skeleton was built of series of parallel chambers, which excludes the possibility that these were external body covers. The chambers apparently represent walls of hydraulic skeleton units, resembling the basement membrane of chaetognaths or the notochord sheath of primitive chordates. Such chambers are widespread among the earliest fossil animals represented by fossils preserved in sandstone. The rise and fall of the Ediacaran faunas thus seem to be partially preservational artifacts. The range of its occurrence is a result of two successive evolutionary events: the origin of an internal hydraulic skeleton enclosed by a strong basement membrane, and the appearance of decomposers with abilities to disintegrate such collagenous sheaths.

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