Neues Jahrbuch für Geologie und Paläontologie, Monatshefte 2002
Internal anatomy of a new Precambrian dickinsoniid dipleurozoan from northern Russia

Jerzy Dzik & Andrey Yu. Ivantsov
Instytut Paleobiologii PAN, Twarda 51/55, 00-818 Warszawa, Poland. e-mail:

Abstract. Current controversy over the nature of biotic changes at the Precambrian-Cambrian boundary centres on whether the Ediacarian organisms were metazoans or not. A new dickinsoniid of the Dickinsonia tenuis group from a recently discovered fossiliferous horizon at the White Sea shore, Russia, exquisitely preserved in fine sediment, offers the needed anatomical evidence. In several specimens which show the originally high convexity of the body, the dorsal segmented unit (normally being the only preserved structure in the dickinsoniids) was specifically deformed under the sudden sediment load. In result, dense internal organs are reproduced as furrows on the lower bedding surface, whereas those which easily collapsed as oval elevations. This pattern corresponds to the distribution of probable intestinal caeca in Dickinsonia costata and probable gonads in the related dipleurozoan Yorgia. A pharyngeal structure is represented by a circular imprint and the intestine by a wide axial furrow. Apparently, the new dickinsoniid together with Spriggina and several other Ediacarian genera represents a single clade, characterised by dorsally located metameric hydraulic skeleton, serially arranged gonads, and metameric intestinal caeca.