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Vendobionta and Psammocorallia: Lost Constructions of Precambrian Evolution Journal ofthe Geological Society, London, Vol. 149, 1992, pp. 607-613, 6 figs. Printed in Northern Ireland Vendobionta and Psammocorallia: lost constructions of Precambrian evolution A. SEILACHER Geologisches Institut der Universitat Tiibingen, Sigwartstr. 10, 7400 Tiibingen, Germany and Kline Geology Laboratory, Yale University, POB 6666, New Haven, CT 06511, USA Abstract: The non-availability of biomineralized skeletons and lowlevels of predation led Vendian evolu- tion along strange avenues. The Ediacara-type Vendobionta appear to represent a inkingdom, which foliate shapes, large sizes and the necessary compartmentalization were achievedby quilting of the skin rather than by multicellularity. Psammocorallia, in contrast, are interpreted as coelenterates that constructed an internal sand skeleton. Both were immobile soft-bottom dwellers that had high population densities, and both became preserved by obrutional accidents; thus they render ‘fossil snap shots’, in which the original distributional patterns, age structures and standing biomasses of populations are accurately recorded. With the exception ofstromatolites, a small cone-shaped Vendobionta. As the organisms grew, either new quilts were calcareous fossil of problematic affiliation (Cloudinu) and a inserted marginally or existing units expanded and became number of small organic-walled fossils, known Precambrian subdivided fractally. Both modes have the result that quilts do organisms were largely soft-bodied. How the general lack of not exceed acertain diameter. This construction limits the biomineralization was related to the chemistry of the Precam- available morphospace in three ways. (1) Quilts never bundle, brian ocean is a matter of discussion, but means that the bio- but are added in one plane to make foliate bodies that may logical sink for carbonatewas in any case rather different from reach almost one metre in size but are only a few millimetres that in Phanerozoic oceans. On the other hand, preservational thick. (2) The quilt pattern and relief was the same on either ‘snapshots’ of communities suggest that the standing biomass side of the carpet, as can be verified in specimens that became was not significantly lower than in equivalent modern environ- partly folded-over before being cast (Fig. 3). (3) Individual ments, at least with regard to the epibenthic realm. quilts never protrude beyond the common margin to form On the basis of constructional and preservational features, branches, tentacles or appendages. threekinds of Vendian macro-fossils can be distinguished: Vendobionta, trace fossils and sand corals (Psammocorallia). Function of quilting The quilted hydrostatic constructionallowed the Vendobionta Vendobionta to maintain a foliate morphology that deviated considerably from a simple balloon shape. Such bodies could, like carpets, As pointed out earlier (Seilacher 1988), the interpretation of rest firmly on the sea floor. At the same time they facilitated Ediacara-type organisms as soft-bodied ancestors of modern direct metabolic exchange with the environment by their metazoan phyla (Glaessner 1984) meets with difficulties. maximized surface-to-volume ratio. If Vendobionta were not Rather, they are considered to be a unique, quilted type of multicellular, the size limits set by Runnegar (1982) would not biological construction that has no counterpartin the modern, apply, since diffusion could be assisted by flow processes. or even the Phanerozoic, biosphere. A joint TiibingenNale At the same time quilting may have served an internal func- expedition to Newfoundland in the summer of 1990 (Mark tion. Plants and animals developed multicellularity to over- Brandon, chief investigator) has yielded additional evidence in come the size limits set for unicellular organisms. In other support of this unorthodox view. In order to emphasize the words: they use the originally reproductive process of cell basic difference, the informal name Vendozoa is here changed division for growth purposes. Subdividing a syncytial proto- to Vendobionta with the following definition. plasm by quilting appears to be a valid alternative, which has Kingdom Vendobionta. Immobile foliate organisms of diverse geo- its analogues in the skeletal chamberlets and canal systems of metries that were only a few millimetres thick, but reached several giant foraminifera, or the quiltedumbrella of Acetubuluriu. So, decimetres in size. A shared characteristic is the serial or fractal quilt- primitive organisms could growto large sizes by integumental ing of the flexible body wall, which stabilized shape, maximized exter- compartmentalization without necessarily becoming multicel- nal surface and compartmentalized the living content. lular; but this development had consequences. As Gould Since no organs can be recognized, this content is thought to have (1989) haspointed out, quiltedcreatures could never have been a Plasmodial fluid rather than multicellular tissue. Included are reached the degree of tissue differentiation required for higher the Petalonamae (Pflug 1972) and a variety of forms previously inter- levels of organization. In addition, they were much more vul- preted as soft-bodied ancestors of metazoan phyla. Range: Vendian. nerable than multicellular organisms. A predator could not Claimed Cambrian survivors seem to showdifferent preservational only swallow the whole organism, but even small bites would properties. probably have led to fatal leakage from the living bags. Thus the disappearance of the Vendobionta at, orbefore, the evolu- tionary radiation of metazoans with hard jaws and claws is not Nature of the quilted construction surprising. Even if the seapen-like fossils fromthe Burgess While overall geometries and symmetries vary agreat deal Shale (Conway Morris 19896, fig. sa) were indeed vendobion- (Fig. l), quilting is the primary shared characteristic of all tan survivors, the picture hardly changes: no such impressions 607 Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/4/607/4892348/gsjgs.149.4.0607.pdf by guest on 25 September 2021 608 A. SEILACHER LIFE STYLES OF BILATERALVENDOBIONTA dh Ernietta Pferidinium Dickinronia Phyllozoon spriggins Fig. 1. As immobile organisms, the Vendobionta depended on sedimentation rates. In areas of low sedimentation they could recline as flat carpets or stand erect, provided that the basal disc or ring sufficed as an anchor in the soft sediment. In areas of increased background sedimentation, the margins grew up to form bag-like sediment stickers. Note that serial and fractal modes of quilting are represented in all three modes of life. Forms from Mistaken Point, Newfoundland (lower right) are not yet formally described. have ever been found in lower Cambrian sandstones that are A special problem are pennate forms with an ‘attachment taphonomically and environmentally more equivalent to the disk’ at their base. In soft sediment, such a disk would be a Ediacara deposits. much poorer anchorthan root-like extensions. One could argue that vendobiontan construction did not allow for the fabrication of such extensions. Alternatively, one might con- styles Life sider these structures to be floats rather than anchors. The latter Whether they lived photo- or chemosymbiotically or simply idea would appear particularly suitable in the case of unde- absorbed dissolved organicsubstances, there is little doubt scribed Churniu-like forms from Newfoundland (Fig. 3), that Vendobionta were immobile. Even though they were pri- whose bases resemble a life-belt or a doughnut rather than marysoft-bottom dwellers, they shared adaptationalprob- being concentrically quilted. Still, biostratinomic evidence lems, and strategies to solve them, with the secondary soft- falsifies this model. While associated species maintain their bottom dwellers derived from sessile animal stocks of later original random orientations, the stalked species are always times (corals, oysters, brachiopods, cirripeds). The vast major- current-aligned with the disks pointing upcurrent. So the rings ity of Vendobionta, including leaf-shaped forms, lived as did function as anchors, although the exact mechanism is not carpet-like recliners in areas where rates of background sedi- yet clear. From their mode of preservation, it appears that the mentation were low enough not to cover them. In Namibia, rings were fluid-filled, like the quilted leaf part. On the other however, the margins of variously quilted carpets grew up- hand, the ring tube far exceeds the diameter allowed for in- wards with sand sedimentation and thustransformed into bag- dividual quiltings in the foliate parts, suggesting different like sediment stickers, the way they have been preserved in the physiological constraints. Is it possible that such a structure sediment (Fig. 1). They may also have become passively re- could also effect scour-implantation, even though its content implanted after scouring,if the ‘rock-in-the-sock’ model of the was not much denser than the water around? Psammocorallia (Fig. 4) is modified into one filled with loose Another problem is the stalk of the Newfoundland ‘sea- sand. pens’. Not only isit much morepronounced than in true Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/4/607/4892348/gsjgs.149.4.0607.pdf by guest on 25 September 2021 VENDOBIONTA AND PSAMMOCORALLIA 609 Fig. 2. Impressions of various Vendobionta buried under an ash layer (chiselled edge in lower part of picture) at Mistaken Point, Newfoundland. Note that only stalked forms are
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