Possible animal body fossils from the Late Neoproterozoic interglacial successions in the Kimberley...

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GR Letter

Possible animal body fossils from the Late Neoproterozoic interglacial successions inthe Kimberley region, northwestern Australia

Zhong-Wu Lan ⁎, Zhong-Qiang ChenSchool of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia

a b s t r a c ta r t i c l e i n f o

Article history:Received 3 December 2010Received in revised form 22 February 2011Accepted 26 May 2011Available online 6 June 2011

Handling Editor: A.S. Collins

Keywords:EdiacaranPalaeopascichnusXenophyophoreKimberleyNorthwestern Australia

New specimens of the enigmatic Ediacara-type fossil Palaeopascichnus have been identified from the upperpart of the Neoproterozoic Ranford Formation in the Kimberley region, northwest Australia. New material ismorphologically similar to Palaeopascichnus and represents the largest species of this genus. They resemblethe present-day xenophyophore protists in chamber morphology and growth patterns, supporting theinterpretation that Palaeopascichnus is possibly a xenophyophore body fossil rather than a trace fossil.Stratigraphic correlation reveals that the new Palaeopascichnus specimens are preserved in the interglacialsuccessions between the Landrigan/Marinoan and Egan/Ediacaran glaciations. If correlation with the earlyEdiacaran formations of South Australia is accepted, this represents the earliest known identifiablemember ofthe Ediacara biota. New fossil record fills the evolutionary gap between the Cryogenian and Ediacaran animalassemblages and well-known Ediacaran biota. The new Palaeopascichnus specimens represent the first recordof Ediacara-type fossils in Kimberley, and suggest the probability that additional Ediacaran fossils may befound in northwestern Australia.

© 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

1. Introduction

The middle–late Neoproterozoic (750–580 Ma) is a critical periodwhen the Earth was repeatedly glaciated, namely the Sturtian,Marinoan and Gaskiers glaciations and large multicellular animals ofthe Ediacaran biota emerged in association with a series of geologicalevents such as Gondwana assembly, true polar wander and eruptionof flood basalts (McCall, 2006; Maruyama and Santosh, 2008; Meertand Lieberman, 2008;Meert et al., 2011). After the Gaskiers glaciation,the well-known Ediacaran biota flourished around the world (Knolland Walter, 1992; Narbonne and Gehling, 2003; Knoll et al., 2004;Grey, 2005; McCall, 2006; Jiang et al., 2011). Unlike earlier simple lifeforms, many components of the Ediacara biota are multicellular andcharacterized by extraordinary organisms comprising discs, frondsand segmented morphologies (McCall, 2006). In particular, thebilaterians of the Ediacaran assemblages have also set the macroevo-lution tempo and macroecology in Phanerozoic (Marshall, 2006;Peterson et al., 2008). Knowledge of the Ediacaran life however hasbeen obtained mainly from several well-known fossil localities: theFlinders Ranges of South Australia, White Sea of Russia, MistakenPoint of Newfoundland, Canada and Namibia of Africa and sporadicreports from other localities around the world (see McCall, 2006 forreview). Most of them disappeared with the advent of diverse skeletal

bilaterian metazoans during the ‘Cambrian Explosion’, and thus areconfined to a time interval of 575–542 Ma (Narbonne, 2005).

Growing evidence shows that multicellular organisms may haveoccurred earlier in the early Ediacaran and Cryogenian times even inthe Mesoproterzoic (Bengtson, 1998; Li et al., 1998; Seilacher et al.,1998; Xiao et al., 1998; Rasmussen et al., 2002, 2004; Yin et al., 2007).For example, sponge biomarkers from theMarinoan glacial deposits inOman suggest the emergence of animals during the late Cryogenian(Love et al., 2009). Annuli and disc-like Ediacara-type fossils from thepre-Marinoan Twitya Formation, Windermere Supergroup in theMackenzie Mountains, northwest Canada (Hofmann et al., 1990) andproblematic sponge fossils from the pre-Marinoan sediments in SouthAustralia (Maloof et al., 2010) indicate that multicellular animals mayhave occurred in the Cryogenian (Table 1). These Cryogenian and pre-Gaskiers glaciations and Ediacaran organisms are also importantbecause they may have set an agenda for the diversification ofEdiacara-type assemblages in the late Ediacaran times. They remain,however, poorly understood because of insufficientmaterial for study.Thus, additional material of the middle-late Neoproterozoic fauna iscrucial in understanding of origination and macroevolution of theEdiacaran life.

In Australia, apart fromSouthAustralia, the completeNeoproterozoicsuccessions are also exposed in central Australia and the Kimberleyregion of northwest Australia (Grey and Corkeron, 1998; Corkeron,2007). In the Kimberley, the Cyrogenian−Ediacaran successions areN1500 m thick and correlate well with their counterparts in SouthAustralia (Table 1). However, no certain Ediacara-type fossils have beenreported from Kimberley, although new discovery of Ediacaran fossils is

Gondwana Research 21 (2012) 293–301

⁎ Corresponding author. Tel.: +61 08 64881204; fax: +61 08 64881037.E-mail address: [email protected] (Z.-W. Lan).

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anticipated in this region (McCall, 2006). Previously, Sprigg (1949)named the possible fossil Protoniobia wadea from theMount John ShaleMember of Kimberley and considered it to be related to the Ediacaranfauna from South Australia. However, the Mount John Shale Member isstratigraphically below the Eliot Range Dolomite whichwas assigned tothe early to middle Neoproterozoic in age by stromatolite biostrati-graphic correlation (Grey and Blake, 1999). The Mount John ShaleMember therefore is not younger than early Neoproterozoic in age.These fossils are also highly questionable. Dunnet (1965) documentedseveral star-shaped and jellyfish-like structures from the RanfordFormation of the Mount Brooking area, East Kimberley and interpretedthe former as inorganic structures and the latter as jellyfish fossils. Theassignment of jellyfish-like structures to jellyfish fossils was rejected byCloud (1968) who considered these Kimberley structures are inorganic.The latter view was followed by Grey (1981a, b) when she reportedadditional materials from the Ranford Formation of the Brooking area.

More recently, several Palaeopascichnus-like structures werefound from the Neoproterozoic Ranford Formation in the Kimberleyregion, northwestern Australia. These Kimberley specimens aremorphologically similar to Palaeopascichnus specimens in all observedaspects, but are preserved in dolomitic siltstone and are much largerthan any known species. New material therefore provides anadditional example of the early-middle Ediacaran biota and providessome insights into affinities and macroevolution of this enigmaticEdiacaran genus, suggesting the probability that additional Ediacara-type fossils may be found in northwestern Australia.

2. Geological and stratigraphic settings of new material

The Kimberley region is located in northwestern Australia (Fig. 1a).Here, the Neoproterozoic successions are unconformably underlain bythe Kimberley Group of Palaeoproterozoic age (McNaughton et al.,1999), and overlain by the Cambrian Antrim Plateau Volcanics (Hanleyand Wingate, 2000). The new material was collected from the upperpart of the Ranford Formation exposed at the Donkey Gap section (GPS:S16°03′38.7″; E128°57′44.2″) of the Mount Brooking area, EastKimberley, near Western Australia-Northern Territory border(Fig. 1b). In East Kimberley, the Neoproterozoic sequences include theDuerdin and Albert Edward Groups. The former comprises the FargooFormation, Frank River Sandstone, Moonlight Valley Formation andRanford Formation, and the latter group consists of the Mount FosterSandstone, Elvire Formation, Boonall Dolomite, Timperley Shale,Nyuless Sandstone, and Flat Rock Formation (Fig. 2a; Table 1). Ofthese, the Fargoo and Moonlight Valley Formations are considered asequivalents of the Elatina glaciation (Corkeron, 2007), whereas theBoonall Dolomite is correlated with the Egan Formation of theneighbouring Mount Ramsay area, West Kimberley and both unitswere referred to as the equivalent of the Gaskiers glaciation ofNewfoundland (Grey and Corkeron, 1998; Table 1).

Overlying the Moonlight Valley Formation, the Ranford Formationcomprises three lithologic members: the alternating mudstone andsiltstone of the Lower Member; massive sandstone of the JarradSandstone Member; shale interbedded with siltstone of the Johnny

Table 1Neoproterozoic stratigraphic correlations between the Kimberley region and South Australia [modified from Grey and Corkeron (1998), Grey and Calver (2007) and Grey (2008)].

MOUNT RAMSAY EAST KIMBERLEY AMADEUS BASIN ADELAIDE RIFT COMPLEX

Hawker GroupArumbera 3 & 4Antrim Plateau Volcanics Antrim Plateau Volcanics Ca

mb

ria

n

Rawnsley QuartziteFlat rock FormationLubbock Formation

Tean Formation Nyuless Sandstone b

Ediacaran member

McAlly Shale Chace Quatzite member

Yurabi Formation

Timperley Shale

Arumbera 1 & 2

Po

un

d S

ub

gro

up

Bonney Sandstone

Egan Formation Boonall Dolomite Julie Formation Wonoka Formationa

Bunyeroo FormationElvire Formation

Lo

uis

a D

ow

ns

Gro

up

Alb

ert

Ed

wa

rd G

rou

p

Mt. Forster Sandstone ABC Range Quartzite

Mt. Bertram Sandstone Ranford Formation

Wirara Formation Johnny Cake Shalec

Stein Formation Jarrad Sandstone

Pertatataka Formation

Wil

pe

na

Gro

up

Brachina Formation

Ed

iaca

ran

gla

cia

tio

n

Ed

iaca

ran

Ku

nia

nd

i G

rou

p

Landrigan Formation

Du

erd

in G

rou

p

Moonlight Valley Formation

Frank River Sandstone

Fargoo Formation

Olympic Formation Nuccaleena Formation

Elatina Formation

Aralka Formation Tapley Hill Formation

Ma

rin

oa

n

gla

cia

tio

n

Domical form (Grey and Corkeron, 1998)

Tungussia julia (Grey and Corkeron, 1998) a

Palaeopascichnus (Haines, 2000) b

Palaeopascichnus (Gehling and Droser, 2009) c

Palaeopascichnus (this paper)

Areyonga Formation Um

be

rata

na

Gro

up

Sturtian Tilllite

Stu

rtia

n

gla

cia

tio

n

Cry

og

en

ian

294 Z.-W. Lan, Z.-Q. Chen / Gondwana Research 21 (2012) 293–301


Cake ShaleMember (Dow and Gemuts, 1969; Thorne et al., 1999). TheLower member is only exposed in the Texas Downs area, whereasother members are widespread in the entire East Kimberley region(Thorne et al., 1999). In particular, the extremely thick sandstone,with single beds up to 2.5 m in thickness, of the Jarrad SandstoneMember form a spectacular geological marker in the field, and thusdistinguishes the Ranford Formation from other late Neoproterozoicstratigraphic units in Kimberley. In the Kununurra area, the JarradSandstone Member and the underlying Moonlight Valley Formation

are exposed at the Keep River National park area of NorthernTerritory, whereas the Johnny Cake Shale Member crops out in theDonkey Gap area (Fig. 1b). At the Donkey Gap section, the upperRanford Formation is well exposed and is characterized by alternationof claystone, dolomitic siltstone and fine sandstone. The newmaterials described below are preserved in a 2-m-thick successionof claystone and dolomitic siltstone at the upper Johnny Cake ShaleMember, which was deposited in a lacustrine setting (Dunster et al.,2000; Fig. 2b). Consequently, the new material came from the

Fig. 2. (a) Neoproterozoic sequences in East Kimberley area. (b) The logged upper Ranford Formation exposed at the Donkey Gap section showing the fossil horizon ofPalaeopascichnus and star-shaped forms.

Fig. 1. (a) Location of the Donkey Gap section near Kununurra, East Kimberley, northwestern Australia. (b) Simplified geological map showing the distribution of the lateNeoproterozoic Duerdin and Albert Edward Groups in the East Kimberley region and location of the Donkey Gap section.

295Z.-W. Lan, Z.-Q. Chen / Gondwana Research 21 (2012) 293–301


interglacial succession between the Moonlight Valley Formation andEgan Formation/Boonall Dolomite. These two glacial successions arecorrelated with the Landrigan/Marinoan and Egan/Ediacaran glacia-tions, respectively (Grey and Corkeron, 1998; Corkeron, 2007; Table 1).Reliable chronostratigraphic correlation is currently unavailable amongthe interbasinal correlations in Australia. Tillite lithostratigraphiccorrelation and carbon isotopic profiles incorporatingwith stromatoliteand acritarch biostratigraphic correlations suggest that the MoonlightValley Formation and its cap carbonate is contemporaneous with theElatina and Nuccaleena Formations of Adelaide Rift Complex, SouthAustralia, respectively (Grey and Corkeron, 1998; Corkeron, 2007; Greyand Calver, 2007; Grey, 2008). As a result, the upper Ranford Formationis correlative with the Brachina Formation in South Australia (Grey andCorkeron, 1998; Corkeron, 2007; Table 1).

In addition, the previously reported star-shaped structures(Dunnet, 1965; Cloud, 1968; Grey, 1981a, b) are also present in theupper Johnny Cake Shale Member. They occur in the dolomiticsiltstone succession, but do not share the same bedding plane surfacewith Palaeopascichnus-like structures described below (Fig. 2).

3. Systematic palaeontology

Family and above classification units are uncertain.

Genus PALAEOPASCICHNUS Palij, 1976, emended, Shen et al., 2007Type species. Palaeopascichnus delicatus Palij, 1976.Palaeopascichnus sp. nov.

3.1. Diagnosis

A series of large, subcircular crescents that possess the length up to51 mm and the width up to 9 mm. Series aligned straight, curved orbranching. The thin spacing/gap separating crescents varies from0.5 mm to 3 mm in width.

3.2. Description

All specimens are flattened, preserved parallel to bedding surface,and contain no carbonaceous materials. They are characterized by aseries of large, subcircular crescents separated by a thinner spacing(Fig. 3). Crescents are curved to the same direction. Each crescent isnearly consistent in width and they are parallel to each other. Eachcrescent has a sub-rounded end and lacks internal ornamentation.Crescents are bounded by a narrow spacing, but never coalesce laterallyto form meandering loops of trace fossils. Individual crescents areclustered and aligned into straight (Fig. 3f), curved (Fig. 3b), orbranching (Fig. 3d) series, but never merged or overgrown on eachother. Specimens UWAKE002 and UWAKE003 are preserved on thesamebeddingplane,whereas specimenUWAKE001onanotherbeddingplane. However, both of the Palaeopasichnus-bearing rocks arecomposed of laminated siltstone, and all these three Palaeopasichnusspecimens are covered with sandstone veneers. Each crescent has thesame mineral compositions as the host rock. Sizes of individualcrescents vary from 20 to 51 mm in length and 2 to 9 mm in width(Fig. 4). The spaces between crescents are 0.5–3 mm wide, but have alength of 18–50mm.

3.3. Material

Three specimens (UWAKE001, UWAKE002 and UWAKE003) areused in this study.

3.4. Occurrence

Johnny Cake Shale Member, Ranford Formation at the Donkey Gapsection of the East Kimberley Region, northwestern Australia.

3.5. Discussion

When compared with the type species Palaeopascichnus delicatusPalij, 1976, the Kimberley specimens have similar crescents andgrowth patterns. Their crescents are bounded by a narrow spacing,but never coalesce laterally to form meandering loops of trace fossils.Individual crescents are clustered and aligned into straight, curved orbranching series, but never merged or overgrown on each other.These characteristics suggest that both the Kimberleymaterial and thetype species are cogeneric. P. delicatus cannot, however, accommodatethe new material because the latter possesses much larger andsubcircular crescents. In fact, all of the known Palaeopascichnusspecies and Palaeopascichnus-like fossils have crescent width varyingfrom 0.1 to 3 mm and length ranging from 0.3 to 10 mm (Fig. 4), andthus are easily distinguished from the Kimberley material, althoughthey share similar crescent growth patterns. As a result, the Kimberleyspecimens may represent a new species of Palaeopascichnus. Thispotential new species cannot be fully defined herein due toinsufficient material.

The straight to slightly curved uniserially alignment of crescents(Fig. 3f) is reminiscent of P. minimus Shen et al. (2007, Figs. 8.1-8.5)and P. sp. figured by Gehling and Droser (2009, Fig. 7B). However,both P. minimus and P. sp. differ from the new material in havingmuch smaller isomorphic crescents and the series alignment ofcrescents that is consistent in width throughout their seriesextending direction (Shen et al., 2007; Gehling and Droser, 2009).In contrast, the Kimberley specimens possess large isomorphiccrescents, N20 mm long and N2 mm wide (Fig. 3f) and the alignmentof crescents varies in width throughout their series extendingdirection (Fig. 3f).

The curved uniserially alignment of crescents (Fig. 3b) recalls P. sp.figured by Cope (1983, pl. 2, Fig. 2) and P.meniscatus Shen et al. (2007,Figs. 8.6-8.7). However, the series of crescents of the latter two arestrongly curved and nearly U- or V-shape in outline at turning points.Their crescents contact closely one another and are consistent inlength along series extending directions. In contrast, the crescents ofthe new material curve at a relatively low angle when approachingends, and are not consistent in crescent length along the seriesextending direction (Fig. 3b). Accordingly, these two species aredistinguished from the Kimberley specimens. The curved uniseriallyalignment of crescents of the new material (Fig. 3b) also resemblesP. sinuosus illustrated by Fedonkin (1985, 1990). However, P. sinuousis characterized by several (more than two) sinuous turnings alongthe series extending direction, whereas only one turning is seen in theKimberley specimen (Fig. 3b).

The new material also superficially resemble P. jiumenensis Donget al. (2008, Fig. 7) in uniserially straight to curved alignment ofcrescents (Fig. 3b, f). The latter, however, clearly differs from the newmaterial in having crescents that are nearly spherical in outline andsurrounded by halos of microcrystalline quartz grains. Moreover, thecrescents of P. jiumenensis are connected by an organic filament alongseries extending direction, which are absent in the new specimens(Fig. 3b, f).

The new material may be confused with the well-illustratedP. delicatus specimens (Palij, 1976, pl. XXIV; Palij et al., 1983, pl. L,Figs. 4–7, pl. LXI, Figs. 2–3; Paczesna, 1986, pl. I, Fig. 2; Narbonne et al.,1987, Fig. 6B; Gehling et al., 2000, pl. 1, Fig. 3) as they both have theuniserially straight to curved crescent alignment. However, thecrescent series in P. delicatus remain constant in width along theseries extending direction and individual crescents show straight,rod-like, circular or ring morphology. P. delicates therefore is readilydifferentiated from the Kimberley specimens.

Branching alignment of crescents of the Kimberley specimens(Fig. 3d) is comparable with that of the South Australian materialnamed P. sp. by Glaessner (1969, Figs. 5C, D), Haines (2000, Figs. 6, 7)and Gehling and Droser (2009, Fig. 7C). However, the South Australian



specimens can be differentiated from the new material by their well-defined, multiple branching crescent series, which may have thethird-order branches. Some branches are also merged or overlapped

each other (Haines, 2000, Figs. 6, 7). By comparison, the Kimberleyspecimens (Fig. 3d) only branch once and the branches are neithermerged nor overlapped each other.

Fig. 3. Large Palaeopascichnus preserved as negative epirelief on bedding plane. (a) Slab photo showing the presence of specimen UWAKE002 and UWAKE003 in the same beddingsurface. (b) An enlargement of the curved specimen (UWAKE002) comprising 11 crescent segments, each of which is separated by a thinner spacing. (c) Line drawing of (b). (d) Anenlargement of the branching form specimen (UWAKE003) composed of 26 crescents on the primary branch and 2 crescents on the second branch. (e) Line drawing of (d).(f) Specimen UWAKE001 comprising 13 crescent segments, each of which is separated by a very thin gap and not laterally connected. (g) Line drawing of (f). All specimens arehoused at the School of Earth and Environment, The University of Western Australia, Perth.



4. Taphonomy

The known Palaeopascichnus species have been preserved asmoulds or casts (Dong et al., 2008). New material is preserved innegative epirelief on the upper surface of bedding plane. It should benoted that many fossil-like structures from the Precambrian succes-sions may be produced due to strong weathering (Seilacher, 2007).However, several biological structures such as chamber-like crescentsand lozenge-shaped elements at crescent margins are distinct in theKimberley specimens. These structures couldn't be generated byweathering, which may produce irregular, uncertain structures. Therelatively densely arranged, fresh minerals in petrographic imagesalso show no sign of weathering on the Palaeopascichnus-bearingdolomitic siltstone. In addition, laminae are abundant and associatedwith Palaeopascichnus-like structures (Fig. 5d). When laminae areexposed along an oblique surface to bedding plane due to physicalweathering, a series of laminae and the gaps between laminae may beconfused with the spacing between two crescents and crescents,respectively. However, laminae are usually straight and extendlaterally. They do not terminate unless the laminae are buried byother sediments or broken. In contrast, the spacing between crescentsare curved and terminated by crescent margins (Fig. 3a, c, e, g).Accordingly, natural weathering did not affect fossil preservation inthe Kimberley collection.

Of particular interest is the branching pattern of crescents, which isanalogous to the Palaeopascichnus-like structures from the WonokaFormation of South Australia (Haines, 2000). The pronouncedcrescents bear remarkable resemblance with the sausage-shapedchambers of modern xenophyophore protists (Seilacher et al., 2003;Seilacher et al., 2005). Thus, the crescents and their thin spacings andmargins were interpreted as the fossilized multi-nucleate protoplasmand outer walls enveloping the protoplasm of xenophyophore,respectively (Seilacher, 2007). They were both replaced with andreinforced by agglutinated siliciclastic sediments upon diagenesis(Seilacher, 2007). It should be noted that some of the present-dayinfaunal xenophyophore such as Occultammina profunda have beenproved to be associated with foraminifera functioning as trappingorganicmatter (Rona et al., 2009). Although the pronounced crescentsand their growth pattern somewhat are similar to some meanderingtrace fossils, the Palaeopascichnus specimens are excluded from tracefossils due to lack of ‘turn-around’ connection at crescent margins. Atrace fossil without meandering origin together with an algal originhas also been proposed to accommodate Palaeopascichnus, but allthese interpretations are not well grounded (Shen et al., 2007; Donget al., 2008 and references therein).

Sand veneer remnants occur occasionally on the bedding planesurface of the Palaeopascichnus-bearing siltstone (Fig. 3a). Sandveneer comprises fine quartz grains and clay minerals (Fig. 5a), likethe host rock (Fig. 5b). Crescents are composed of silt-sized quartzgrains and clay minerals, identical to those of the host rocks (Fig. 5c).A layer of thin dark lamina is present near the bedding upper surfaceand dominated by fine crystalline dolomite and argillaceous/siltymaterial (Fig. 5a). This thin lamina (Fig. 5a), together withmica grainsorientated parallel to bedding plane at the top (Fig. 5a), probablyindicates the existence of wrinkle structures/microbial mats (Mataand Bottjer, 2009), which are also commonly present in associationwith Palaeopascichnus in the field (Fig. 5d). Microbial mats were laterdegraded in the anoxic zone with the possible involvement of decayinducing bacteria (e.g. sulphate reducing bacteria) which wasaccompanied by the simultaneous formation of fine carbonate grain

Fig. 4. Crescent size ranges of Palaeopascichnus specimens (f) (UWAKE001),(b) (UWAKE002) and (d) (UWAKE003). Other taxa are after Shen et al. (2007) andDong et al. (2008).

Fig. 5. Transverse thin-section photomicrographs of Palaeopascichnus, host rock andsand veneers. All sections were cut from Specimen (UWAKE001) and perpendicular tobedding surface. (a) Sand veneer composed of clay mineral and fine quartz grains. Notea thin, dark lamina is prominent near the bedding surface and mica grains (marked bywhite arrows) are oriented parallel to bedding plane, which are characteristics ofwrinkle structures preserved in siliciclastic rocks (Mata and Bottjer, 2009). Scale barapplicable to b and c. (b) Host rock comprising clay mineral and fine quartz grains.(c) Palaeopascichnus crescents having the same mineral composition as the host rock.(d) Microbial mat from the same horizon as Palaeopascichnus of the upper RanfordFormation at the Donkey Gap section.



and pore-filling argillaceous material of probably volcanic origin(Schieber, 1998; Seilacher, 1999; Kühl et al., 2003). Microbes sealedthe animal bodies and generated microbial coatings soon afteranimal's death. The microbial envelopes generated a local near anoxicenvironment and thus prevented decay of soft bodies, devouring byscavengers, and disarticulation of complete bodies due to disturbanceby currents or waves. The external moulds of Palaeopascichnus-likeorganisms functioned as early diagenetic sole veneers. The microbialmats resulted from bacterial precipitation smothered decayingPalaeopascichnus bodies, like the ‘death mask’ model interpreted byGehling (1999) for the perseveration of most of soft-bodied Ediacarananimals.

5. Significance of new material

Palaeopascichnus is morphologically distinct from other Ediacara-type fossils or ichnofossils and widely recognized in the Neoproter-ozoic fossil records (Table 2). It is also among the most characteristictaxa of Ediacara biota. This genus was originally established toaccommodate the specimens described from the Ediacaran claystoneof the White Sea, Russia (Palij et al., 1983). The type speciesP. delicatus Palij was interpreted as a burrow-like ichnospecies (Palijet al., 1983). Later, these Palaeopascichnus-like structures have beenremoved from the Ediacaran ichnoassemblage (Haines, 1990, 2000,Gehling et al., 2000; Jensen, 2003; Seilacher et al., 2003, 2005; Jensenet al., 2006; Seilacher, 2007; Shen et al., 2007; Dong et al., 2008). Thesimilar structures preserved in carbonates have been interpreted asalgae (Haines, 1990, 2000) or stratiform stromatolites (Runnegar,1995). Gehling et al. (2000) considered that these structures asbacterial colony, algae, egg masses or even serially arranged buddingspecimens of large Aspidella. Seilacher et al. (2003) interpreted themas body fossils of xenophyophore protists. Its analogues have alsobeen seen in modern deep seas (Seilacher et al., 2003, 2005; Seilacher,2007). Dong et al. (2008) considered that their Palaeopascichnusspecimens may represent the fossilized agglutinated foraminifera.However, the exact morphology and affinities of these organisms stillremain enigmatic (Jensen et al., 2006).

Crescents of the new material are consistent in width and length,and thus, can be distinguished from synaeresis cracks, which vary in

width. Moreover, the latter are characterized by discontinuous orspindle-shaped morphology (Plummer and Gostin, 1981), which areabsent in ourmaterial. The crescent features of the Kimberleymaterialagree well with Palaeopascichnus.

To date, Palaeopascichnus and similar structures have been reportedfrom a variety of facies settings from tuff, carbonates, cherts, claystone,siltstone to sandstone from the Ediacaran successions (Table 2). Newmaterial is preserved in dolomitic siltstone as it is in the WonokaFormation of the Adelaide Geosyncline (Haines 2000). As outlined inTable 2, the known Palaeopascichnus species occurred in the strataequivalent to, or younger than, the Julia and Wonoka Formations ofcentral and South Australia. In contrast, the Ranford Formationrepresents the interglacial sequence between the Landrigan/Marinoanand Egan/Ediacaran glaciations (Table 1). If the previous stratigraphiccorrelations (Grey and Corkeron, 1998; Corkeron, 2007; Grey andCalver, 2007; Grey, 2008) are followed, the Ranford Formation is clearlyolder than the Julia and Wonoka Formations. The Ranford Formationmaterial therefore represents the oldest specimens of Palaeopascichnus.As mentioned above, the possible animal fossils have been detectedfrom the Marinoan glacial successions and pre-Marinoan sediments(Hofmann et al., 1990; Love et al., 2009; Maloof et al., 2010). The newspecimens fill the animal evolutionary gap between the Marinoan/orpre-Marinoan assemblages and the well-known Ediacaran biota.Moreover, the oldest Palaeopascichnus species has the largest bodysizes, whereas the younger species usually have smaller body size(Fig. 4; Table 2). We speculate a decline in body size along theevolutionary lineage is consistent with increasing competitive pressurein the late Ediacaran oceans.

In addition, although Palaeopascichnus is one of the most commonEdiacaran fossils and has been reported worldwide, its presence at theRanford Formation represents the first record of Ediacara-type fossilsin Kimberley, shedding new light on further discovery of Ediacara-type fossils in this vast region.

6. Conclusions

Newspecimens of the enigmatic Ediacara-type fossil Palaeopascichnushave been identified from the upper Ranford Formation in the Kimberleyof northwestern Australia. If correlation with the early Ediacaran

Table 2Geographic and stratigraphic distribution of Palaeopascichnus.

Species References Stratigraphical unit Lithology Age Locality

P. jiumenensis sp. nov. Dong et al. (2008) Liuchapo Formation Chert 551–542 Ma (Post-Gaskiersglaciation)

Eastern Guizhou, South China

P. minimus sp. nov. Shen et al. (2007) Zhengmuguan Formation Claystone Post-Gaskiers glaciation Helanshan, northern ChinaP. meniscatus sp. nov. Shen et al. (2007) Zhengmuguan Formation Claystone Post-Gaskiers glaciation Helanshan, northern ChinaP. sp. Haines (2000) Wonoka Formation Carbonate Post-Gaskiers glaciation South AustraliaP. sp. Gehling and Droser

(2009)Ediacara Member, PoundSubgroup

Sandstone Post-Gaskiers glaciation South Australia

P. sp. Cope (1983) Coomb Volcanic Formation Tuff 560±1 Ma to 566±2 Ma(Post-Gaskiers glaciation)

Carmarthen area, Dyfed, Wales

P. delicatus Palij Gehling et al. (2000) Fermeuse Formation Sandstone Post-Gaskiers glaciation Avalon Peninsula, eastern NewfoundlandP. delicatus Palij Narbonne et al.

(1987)Chapel Island Formation Siltstone Post-Gaskiers glaciation Fortune Head, Burin Peninsula, southeastern

NewfoundlandP. delicatus Palij Palij et al. (1983) Kanilov Formation Sandstone Post-Gaskiers glaciation Dniester Basin of Podolia, the White Sea, RussiaP. delicatus Palij Fedonkin (1990) Mogilev Formation Sandstone 541±4 Ma (Post-Gaskiers

glaciation)Dniester Basin of Podolia, the White Sea, Russia

P. delicatus Palij Paczesna (1986) Khmelnitski Formation Sandstone Post-Gaskiers glaciation Dniester Basin of Podolia, the White Sea, RussiaP. delicatus Palij Fedonkin (1981,

1990)Ust Pinega Formation Sandstone 555.3±0.3 Ma (Post-Gaskiers

glaciation)Zimny Coast of the White Sea, Russia

P. sinuosus Fedonkin Fedonkin (1990) Ust Pinega Formation Sandstone 555.3±0.3 Ma (Post-Gaskiersglaciation)

Letny Coast of the White Sea, Russia

P. sp. Grazhdankin (2004) Ust Pinegia Formation Sandstone 555.3±0.3 Ma (Post-Gaskiersglaciation)

The White Sea, Russia

P. delicatus Palij Palij et al. (1983) Unnamed clayey beds Claystone Post-Gaskiers glaciation River Syuzma, Onega PeninsulaP. delicatus Palij Paczesna (1986) Lublin Formation Sandstone Post-Gaskiers glaciation Lublin region, southeastern Poland



formations of South Australia is accepted, this represents the earliestknown identifiable member of the Ediacara biota. New materialresembles the modern xenophyophore protists in chamber morphologyand growth patterns. This supports the interpretation that Palaeopascich-nus is a xenophyophore body fossil rather than a trace fossil. The newfossils came from the interglacial succession between the Marinoan andGaskiers glaciations of late Neoproterozoic, and thus, predated the well-known Ediacaran biota and represent the oldest known species ofPalaeopascichnus. The new species also represents the first record ofEdiacara-type fossils in the Ediacaran sequence of Kimberley, northwest-ern Australia.

Acknowledgements

Ms Cynthja Bolton is thanked for photographing the samples. Weare also grateful to Adolf Seilacher, James Gehling and Peter Haines fortheir constructive suggestions and advice for this study. Criticalcomments and constructive suggestions from two anonymous re-viewers and the handling editor Alan Collins have greatly improvedthe quality of this paper. ZWL's Ph.D. study is supported by a jointscholarship from China Scholarship Council and The University ofWestern Australia. This study was also supported by an AustralianResearch Council discovery grant (DP0770398 to ZQC).

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