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 unitsexpanded 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 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 ClaimedCambrian 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 primaryshared characteristic of all tan survivors, the picture hardly changes: no such impressions 607

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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 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

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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 current-orientated, probably by felling rather than transport. Later, the impressions became tectonically deformed, roughly in the direction-of the pre-existing slope. Diameter of coin atleft hand margin is 1.7cm.

Fig. 3. Ashfall produced a downslope current, the direction of which is recorded by the felling direction of stalked species, the scour in front of a folded-over leaf-shaped form and cross-bedding in the ash layer. Another current direction is recorded by bent tops of stalked species and folding-over of spindle-shaped forms, which also show that top and bottom surfaces looked alike. The block diagram explains relief inversion in the stem parts, in which spindle-shaped organisms that came to lie under the stem are also involved. All drawings made from oriented silicon casts made at Mistaken Point, Newfoundland.

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Charnia, but it also lacks the sharp contours of rings and leaf preservational events.(4) The mere abundanceof Vendobionta parts and is always preserved with oppositerelief. Presumably, on Vendian sea floors, in addition to low levels of predation the stalk was filled with a more solid, gel-like material-the and scavenging, madetheir episodic preservationlikely in spite best such an organism could do to produce a rigid support of an extremely low fossilization potential. structure. This material would have taken moretime to disinte- grateand consequentlywould have produced the inverted Vendian trace fossils collapse relief, without sharp outlines (Figs 2-3), that charac- terizes the stalk portion in all Newfoundland specimens. In contrast to the Vendobionta, the makers of Vendian trace Becoming erect rather than reclining would be alright in a fossils were true, worm-like animals. In order to plough or photosymbiotic organism, but does not agree with bacterial burrow through the sediment, an organism needs the co-ordi- chemosymbiosis at the sediment-water interface. On the other nated action of appendages or cilia, or the ability to move by hand, perfectlypreserved Vendobionta have been found in undulation or peristalsis, as is typical for metazoans. On the NorthCarolina in avolcano-turbidite facies together with other hand, trace fossils share with the Vendobionta an auto- flysch-typeichnofossils (Gibson 1989), indicatingdepths chthonouspreservation, although they do notprovide true below the photic zone.So the trophic modeof the Vendobionta snapshots, because traces recorded on one bedding plane are remains an open question. Possibly theywere more ambivalent not necessarily contemporaneous. in this respect than multicellular organisms. Stratigraphical changesof trace fossil faunas across the Pre- cambrian-Cambrian boundary in many sections of the world have been described by Crimes (1987, 1989, this volume) and Preservational conditions Fedonkin (19906). These workers found a general upward in- Vendobionta are always preserved as mere impressions withoutcrease in diversity, and listed a considerable number of ich- any organic substanceleft behind. Otherwise they occurin very nogenera that are either restricted to the Vendian or continue differentsedimentological situations: atthe bases of storm into thePhanerozoic, as well asa still largernumber that sands in South Australia, below graded ash layers in New- appear in the early Cambrian. Still, a lot needs to be done in foundland, with turbidites in NorthCarolina, orwith determining synonymies among these taxaand in relating them supposedly estuarine inunditesin Namibia. What thesesettings to particular modesof burrowing and feeding strategies, and to have in common is the role of episodic event sedimentation,by coelomate, acoelomate and pseudocoelomate body construc- which the biota became accidentally buried. It hasbeen argued tions. that the absence or low level of bioturbation on Precambrian While increasing diversity meets the expectation, the etho- sea bottoms favoured the preservationof these delicate impres- logical character of Precambrian trace fossils does not. If the sions. I would argue that the mere abundance of Vendobionta radial burrow systems that have been variously described as lying around on the sea floorwas an equally important factor. medusae (Cloud & Glaessner 1982; Fedonkin 1990a, pl. 6, fig. In the Mistaken Point Formation of Newfoundland, the 5) are added to the guided meanders, thereis a surprising com- fossils (about 9 species of Vendobionta plus large ‘medusoid’ plexity of behaviour patterns, reminiscentof those that charac- blobs of problematic origin) occur only on bedding planes thatterize deep sea ichnocoenoses in the Phanerozoic. Such trends had originally been covered by graded layers of volcanic ash may in fact have begun muchearlier. Large radial impressions (Fig. 2). Cross-bedding, discovered by F. Pfluger in the coarser in the early Proterozoic Notenius Formationof northern Aus- bottom parts of these layers, suggests that the ashfalls pro- tralia (Robertson 1960) have been discarded as sand volcanoes duced downslope currents, with a southward directionof flow (Walter 1972). Asconfirmed by S. Dzulynski (pers. comm. that agrees well with the alignment of the stalked ‘sea pens’. 1991), however, the published pictures look much too regular Oncethe tectonic strain has been eliminated, other Vend- for an inorganic origin andresemble radial feeding burrows.So obionta (including the common spindle-shaped formand leaf- the question remains, whether low levels of competition or shaped forms without a basal disk) show random orientations. similartrophic conditions (bacterial mats)made sediment Except for incipient scouring along the upcurrent ofedges some feeders in Precambrian shallow seas behave similarlyto those Vendobionta, there areno erosion marks. Nordid we observe on deep-sea bottoms at later times. any current-swept accumulations of fossils. Thus it is safe to But are all occurrences of Vendobionta shallow marine? assume that the current was weak and did not transport the Greaterdepth has been suggested for theMistaken Point carpets before burial. Formation of Newfoundland(Conway Morris 1989~).The Sudden obrution appears to apply also to the fossil hori- chief argument is the absence of wave-induced features (oscil- zons in Namibia. Blocks in thecollection of H. D. Pflug lation ripples; hummocky cross stratification) and grading in (Giessen) show closely packed bag-like organisms in 3-dimen- the ash layers, which could occurat any depth. Since there are sional preservation (Pflug1973). They are never collapsed, and no trace fossils in this part of the section, the exact palaeo- always maintaintheir original upright life positions, indicating bathymetry remains ambiguous. that they were partly sand-filled during life. Similar bag-like Considering this background, the localities in the Slate Belt forms have also been found in USSR (Fedonkin 1990a, pl. 5, of NorthCarolina gain importance. So far, onlya few figs. 1,4, 5,6;PI. 8, fig. 5; PI. 10, figs 2-3; pl. 12, figs 3, 5; pl. 16, specimens of Pteridinium have been found which undoubtedly figs I, 3, 6). belong to the Vendobionta; but associated are delicate trace Four conclusions can be drawn (l) Vendobionta were im- fossils (Gibson 1989). Among these is a very distinctive form mobile epibenthic organisms. (2) They are likely to occur as that has been attributed to Syringomorpha, but which is better ‘fossil snapshots’, in which population and age density, popu- assigned to Oldhamia. The same species hasbeen found in the lation structure and standing biomassat the dayof the eventare PuncaviscanaFormation of Argentina(Aceiiolaza 1979), registered without the usual taphonomic distortion. (3) These where it is associated with Oldhamia radiata and Nereites, and values can be extrapolated to intervening time slices, in which also with trilobite tracks, in a more typical flysch facies. these organisms failed to leave a record due to the absence of The North Carolinaconnection thus re-opens the argument

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Fig. 4. The internal and organically cemented sand skeleton of Psammocorallia served mainly as an anchor that currents and waves automatically implanted into the sandy substrate. In Protolyella, growth laminae were added mainly on the smooth bottom surface covered by ectoderm. On the flat top (specimens in the collection of Jan Johansson), the digesting endodermal surface was increased, not by radial septa, but by a reticulate sculpture. In tempestitic slabs (Riksmuseet, Stockholm), animals were washed together in life-orientations along the troughs between spill-over ripples, where the muddy part of storm sedimentation has cast not only the skeletons, but also marks of the rocking implantation process. Mickwitzia Sandstone, Sweden. Scale bar is 1 cm.

as to whether Oldhamia is also Vendian in other occurrences The traditional view, that these are scyphozoan medusae (Alaska, New York, Argentina, Ireland, Belgium), or whether whose gastral cavity became sand-filled after death, is unten- it spans the Precambrian-Cambrian boundary. Secondly, the able. Not only would it imply that the medusae were all palaeobathymetry of these deposits becomes relevant for the embedded in upside-down positions, but theradial mesenteries biology (photosymbiotic or not) of the Vendobionta. should appear as recesses, rather than ridges, in a cast. Mor- phology and internal structureare inconsistent with them Psammocorallia being trace fossils (Jensen 1991), though the somewhat similar Erooksella fromthe middle Cambrian of Alabama (Harr- Placing the Vendian medusoids of earlier workers in either the ington & Moore 1956) is actually a radial burrow system. Vendobionta or trace fossils, we are faced with another diffi- In the new interpretation, these fossils are regarded as inter- culty. While bilaterian ancestors are recorded by trace fossils, nal sand skeletons of coelenterates comparable to actinians. where are the rootsof the equally basic group of coelenterates? They were built of sand grains that entered the gastral cavity In addition, DNA sequencing (D. Bridge, Yale, pers. comm.) and then became phagocytized and deposited in place of a suggests that Anthozoa, rather thanScyphozoa, were the most mesogloea between ecto- and endoderm. Originally, this endo- primitive coelenterates. skeleton was rigid, since closely-packed fossils never indent The claim now is that corals are in fact represented in the each other. Nevertheless, soonafter burial worms could Vendian biota, although in an unfamiliar guise (Seilacher burrow right throughthem and compactioncould deform 1990). Some of the putative medusoids are distinguished from them. Thus the cement of these sand skeletons was probably others because of a different kind of preservation. They are organic and after death became readily digested by microbial perfectly circular in outline and either protrude fromsole faces activity. as hemispherical bodies with an unusually high relief (e.g. Functionally, such construction resembles that of solitary Nemiana; Fedonkin 1990a, pl. 5, fig. 3) or they occur on top soft-bottom corals. The massive skeleton provided the im- surfaces as sharply delineated positive epireliefs with irregu- mobile animal with an anchor, notonly by weight but also by larly spaced concentric rings (e.g. Tirasiana). its shape. As conceived in the ‘rock-in-the-sock’ model (Fig. 4), The interpretationof these fossils is not derived from Vend- such an organism would become automatically implanted into ian material, but frombetter known representatives in the a sandy bottom by current or wave scour. In addition, the Mickwitzia Sandstone (lower Cambrian, Sweden; Figs &6) skeleton could be used to increase the area of the digesting andthe Conularia Sandstone (upperOrdovician, Jordan; endodermalsurface by developing reticulate, concentric or Seilacher 1983). Here, they are found in tempestite beds and radial rugosities. always in the same top-and-bottomorientation. Asmooth On the other hand, there are inherent differences between hemispherical base, sometimes with a central dimple, resem- these and the external calcareous skeletons of later corals. As bles assumed actinian burrows (Eergaueria). In the Swedish an internal structure, the sand skeleton did not grow into a material, the upper surfaceof the bodies has a reticulate sculp- cone-shaped theca, into which the soft parts could withdraw, ture made of somewhat finer sand (Protolyella;Fig. 4), or it is nor could it be cemented to hard substrates, Thus there is no finely pitted and bears a variable number(3-5) of strong radial attachment scar even in the smallest individuals. Also the ridges (Spatangopis; Fig. 5). The Jordanian specimens have septa are broad and blunt, in contrast to calcareous septa, narrower and more numerous radial ridges as well as heavy whose sharp edges are dictated by sphaerolithic biomineraliz- concentric rings that continue in cross section into hemi- ation in small blisters indenting the large body pneu. spherical growth laminae (Seilacher 1983). The strange construction of sand corals also had important

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Fig. 5. In Spatangopsis, the bottom surface still has the smooth and rounded bag shape, sometimes with a central dimple. On the endodermal top, however, the surface is not only pitted, but also bears 4-5 heavy and blunt radial septa that variously deform the round outline. In the extreme case (top right) the whole skeleton becomes propeller-shaped, with the ectodermal surface being reduced to a small pad (specimens from Jan Johansson collection). In the slab (Riksmuseet, Stockholm), impressions of tentacles are also preserved. Mickwitzia Sandstone, Sweden. Scale bars are 1 cm.

preservational consequences. In their sandy habitats, fossiliz- preted as gastric casts of medusae (Harrington & Moore 1956). ationpotential was normally minimal because the skeleton However, they are preserved as ironstone concretions and are disintegrated into loose sand before it could leave a lasting actually radial spreite burrowscomparable to Teichichnus impression. Only if instantaneously embedded in fine mud stellutus. Thus, identification of the Palaeozoic Psammocoral- could the shapes of these skeletons be preserved. This is why lia with similar Vendian fossils still needs to be verified. they are foundonly in sandy tempestites, either with the round In any case, the Psammocorallia add another radiation to bottoms sticking out from thesole face, or as complete bodies the history of anthozoans, predating that of the calcitic Tabu- on rippled top surfaces, where they became blanketed by the lata and Rugosa and the much laterone of the aragonitic muddy tail of ,storm sedimentation.Thus, as in the Vend- Scleractinia. The following definition is proposed. obionta, event-induced obrution provides us with fossil Psarnrnocorallia. Radially symmetrical sand bodies, with a smooth, snapshots, in which originalpopulations are portrayed hemisperical lower surface, commonly with a central dimple. Upper directly. surface flat or with a variable number of prominent radial septa and/or The ubiquity of Psammocorallia on sandy bottoms of the concentric growth rings, as well as more delicate ornamentation (reti- lower Cambrian of the Baltic Province is also suggested by culate or tuberculate). In vertical section, surficial growth rings may be another phenomenon. Early stratigraphers coined the name seen to continue intohemispherical sand layers parallel to the bottom Eophyton Sandstone. Today, everybody agrees that Eophyton surface. has nothing to do with algae, but represents tool marks made These fossilshave traditionally beendescribed ascasts of scy- by objectsdragging over themud. Tool marks are regular phozoan stomachs. They are here interpreted as internal sand skeletons features on the sole faces of sandy tempestites deposited in later that stabilized anthozoan polyps living on sandy bottoms. Since these times; but they usually have the shapes of impact casts made by skeletons lost their organic cement soon after death, they could be bouncing shells and shell fragments. The continuous bands of preserved only when smothered by mudfall after a storm, almost in- Eophyton are unique and can be used as time markers in spite of variably in life position. Range: Vendian to Ordovician. Typicalgenus: being pseudofossils. Therefore it is here suggested that sand Protolyella.Other genera: Spatangopsis and variousVendian skeletons, skipped over the ground by storm waves, were in- ‘Medusoids’. volved in the production of Eophyton. In theMickwitzia Sandstone, sandskeletons occur in a vari- ety of shapes that are asyet only partly appreciated. In addition Conclusions to Spatungopsis and Protolyellu, there are ear- and fan-like (1) Megascopic Vendian organisms are difficult to place in forms, some of which bear delicate, bryozoan-like reticulation modern phyla, classes and orders. Rather, they appear to rep- patterns (Fig. 6). Others look like colonies of Fuvosites. resent independent radiations that ultimately could not com- Associated small cones of Volborthellu represent still another pete in metazoan evolution. class of sand skeletons. Possibly there was aplethora of (2) All known groups were benthic, with a shallow, in- unrelated animal groups, including , that all used sand fauna1 tier of worm-like bilaterian sediment feeders (trace instead of biomineralization to make rigid skeletons. But they fossil record) and immobile primary soft-bottom dwellers at also fell under the same preservational constraints. the sediment surface (Vendobionta; Psammocorallia). Thus, Thus it is surprising that nothing similar has as yet been the Cambrian revolution implied probably not only the radia- described from elsewhere in the lower Cambrian. The many tion of biomineralizing metazoan phyla, but also a general specimens of Brooksellu fromthe middle Cambrian of mobilization and an expansion of the zone inhabited by mega- Tennessee resemble Spatungopsis and have likewise been inter- scopic organisms deeper into the sediment and into the open

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Fig. 6. Other fossils with the same preservational charactistics, but of different shapes, are associated with typical Psammocorallia in the Mickwitzia Sandstone (lower Cambrian, Sweden). It is as yet impossible to decide whether they are also sand corals or members of other phyla (e.g. sponges) that used a similar mode of making skeletons. Two fan-shaped bodies in the bottom centre are from the Riksmuseet, Stockholm; the other specimens are in the Johansson collection in Skollersta (Sweden). Scale bars are 1 cm.

water. To test this assumption, one should determine whether FEWNKIN,M. A. 1990~.Systematic description of Vendian Metazoa. In: or not Vendian black shales actually contain remains of nek- SOKOLOV,B. S. & IWANOWSKI,A.B. (eds) The Vendian Sysrem, 1. Springer Verlag, 71-120. tonic organisms. - 19906. Paleoichnologyof Vendian Metazoa. In: SOKOLOV,B. S. & (3) Within the epibenthic zone, standing biomass was sur- IWANOWSKI,A. B. (eds) The Vendian Sysrem, 1. SpringerVerlag, prisingly high; but due toa very low fossilization potential, the 132-137. record of this biota is limited to rare obrution Iagerstatten, in GIBSON,G. G. 1989. Trace fossils from late Precambrian Carolina Slate Belt, which snapshots of Vendian communities are depicted with an south-central North Carolina. Journal of Paleonrology, 63, 1-10. GLAESSNER,M. F. 1984. The dawn of animal life.A biohistoric study. Cam- unusual fidelity. bridge University Press. GOULD,S. G. 1989. Wonderful life. Norton & Co. Field work in Newfoundland (summer 1990) was supported by a NSF HARRINGTON,H. J. & MOORE,R. C. 1956. Protomedusae. In: MOORE,R. C. grant (M. Brandon, chief investigator), with F. Pfliiger studying the (ed.) Treatise on InvertebratePaleonrolog);, Parr F. Coelenterara. Kansas University Press, F. 20-23. sedimentology and H. Luginsland doing extensive silicon casting. The JENSEN,S. 1991. The LowerCambrian problematicum Sparangopsis cosfata discovery of Psammocorallia would have been impossible without J. Torell 1870. Meering Proceedings,Geologiska Forenmgens i Srockholm Johansson, who showed me around in the field and gave access to his Fbrhandlingar, 113, 8C87. large private collection. Additional material has been studied in the PFLUG,H. D. 1972. Systematik derjung-prakarnbrischen Petalonamae Pflug Riksmuseet, Stockholm, with the kind permission of J. Bergstrom. 1970. Palaonrologische Zeitschrift, 46, 56-67. - 1973. Zur Faunader Nama-Schichtenin Siidwest-Afrika IV: Mik- roskopischeAnatomie der Petalo-Organismen. Palaeontographica, Abt. References A, 144, 166-202. ROBERTSON,W. A. 1960. Umbrella-shapedfossils (?) from the LowerPro- ACE~OLAZA,F. G. 1979. El Paleoroico inferior de Argentina segun sus trazas terozoic of the NorthernTerritory of Australia. Bureauof Mineral Re- fosiles. Ameghiniana, 15, 15-64. sources, Records 1960 (1 12). CLOUD, &P. GLAESSNER,M. F. 1982. The Ediacarian Period and System: Metazoa RUNNEGAR,B. 1982. Oxygenrequirements, biology and phylogenetic signifi- inherit the earth. Science, 217, 783-792. cance of the Late Precambrian worm , andthe evolution of CONWAYMORRIS, S. 1989~.South-eastern Newfoundland and adjacent areas the burrowing habit. Alcheringa, 6, 223-239. (Avalon Zone). In: COWIE,J. W. & BRASIER, M.D. (eds) The Precambrian- SEILACHER,A. 1983. PaleoroicSandstones in Southern Jordan: Trace fossils: Cambrian boundary. Oxford Monographs on Geology and Geophysics, 12, Depositional Environments and Biogeography.In: ABED, A. M.& KHALED, 7-39. H. M. (eds) GeologJ, of Jordan, Proceedings oftheFirst Jordanran Geological - 19896. Burgess Shale faunas and the Cambrlan Explosion. Science, 246, Conference. Jordanian Geologists Association, 209-222. 339-346. - 1988. Vendozoa:organismic construction in the Proterozoic biosphere. CRIMES, P. 1987. Trace fossils and the Precambrian-Cambrian boundary. Geo- Lerhaia, 22, 229-239. logical Magazine, 124, 97-1 19. - 1990. Precambrianevolutionary experiments: Vendozoa and Psam- - 1989. Trace fossils. In: COWIE,J. W. & BRASIER, M. D. (eds)The Precam- mocorallia. In: ALBERCH,P. & DOVER,G. A. (eds).The reference points brian-Cambrianboundary. OxfordMonographs on Geologyand Geo- in evolution. Fundarion Juan March, serie Universitaria. 225, 48-53. physics, 12, 166-185. WALTER,M. R. 1972. Tectonicallydeformed sand volcanoes in a Precam- CRIMES,T. P. 1992. Changes in the trace fossil biota across the Proterozoic-Phan- briangreywacke, Northern Territory of Australia. Journal of the Geo- erozoic boundary. Journal of the Geological Society, London, 149, 637-646. logical Societ), of Ausrralia, 18, 395-39.

Received II April 1991; revised typescript accepted 15 December 1991

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