Geology, published online on 30 July 2013 as doi:10.1130/G34691.1 Affi rming life aquatic for the Ediacara biota in China and Australia

Shuhai Xiao1, Mary Droser 2, James G. Gehling3, Ian V. Hughes4, Bin Wan5, Zhe Chen5, and Xunlai Yuan5 1Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA 2Department of Earth Sciences, University of California–Riverside, Riverside, California 92521, USA 3South Australia Museum, North Terrace, Adelaide, South Australia 5000, Australia 4Riverside STEM Academy, Riverside Unifi ed School District, Riverside, California 92507, USA 5Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China

ABSTRACT a maximum thickness of 300 m in incised val- The Ediacara biota has been long championed as a snapshot of the marine ecosystem on ley sections. There are fi ve sedimentary facies the eve of the Cambrian explosion, providing important insights into the early evolution of within the Ediacara Member; the most abundant animals. Fossiliferous beds in the eponymous Ediacara Member of South Australia have been and diverse fossil assemblages occur in laterally recently reinterpreted as paleosols and Ediacara fossils as lichens or microbial colonies that continuous, lenticular, ripple-topped sandstone lived on terrestrial soils. This reinterpretation, here dubbed the terrestrial Ediacara hypoth- beds of the wave-base sand facies (Gehling and esis, would fundamentally change our views of biological evolution just prior to the Cambrian Droser, 2013). This facies represents deposition explosion. We take a comparative paleobiology approach to test this hypothesis. The Ediacara between fair weather wave base and storm wave Member shares a number of forms with assemblages in Ediacaran marine black shales in base, as evidenced by oscillatory ripple marks South China, shales that show no evidence of pedogenesis. Thus, the shared Ediacara fossils, (Fig. DR2) and hummocky cross-stratifi cation. and by extension other co-occurring fossils, are unlikely to have been terrestrial organisms. Ediacara fossils typically cast on the sole sur- A terrestrial interpretation is also inconsistent with functional morphological evidence; some face of overlying beds. Systematic excavation of the shared forms are not morphologically adapted to address the most critical challenges and reassembly of successive 1–30-cm-thick for terrestrial life (e.g., mechanical support and desiccation). Thus, the terrestrial Ediacara fossiliferous beds revealed a number of new hypothesis can be falsifi ed on comparative paleobiological and functional morphological morphologies, including those discussed here. grounds, and we urge paleopedologists to critically reevaluate evidence for pedogenesis in the The Miaohe Member of the uppermost Dou- Ediacara Member and other Ediacaran successions. shantuo Formation in the Yangtze Gorges area is constrained to be older than 551 Ma and it con- INTRODUCTION and taxonomic counterparts in unambiguously sists of as much as 20 m of siliceous black shales Macrofossils from the Ediacara Member of marine environments, then they are probably or mudstones with large carbonate concretions South Australia present many enigmas for pa- marine rather than terrestrial organisms. (Xiao et al., 2002). The Doushantuo Forma- leobiologists, but they also offer an important tion was deposited on an open marine shelf that paleontological window onto the early evolu- STRATIGRAPHIC AND DEPOSITIONAL evolved into a rimmed shelf with connection to tion of marine animals (Narbonne, 2005; Xiao SETTINGS the open ocean (Jiang et al., 2011). Black shales and Lafl amme, 2009; Lafl amme et al., 2013). It Fossil material described herein came from of the fossiliferous Miaohe Member were depos- has been proposed that the fossiliferous Ediacara three Ediacaran units: the Ediacara Member ited in a marine setting, beneath wave reaches, Member of South Australia was modifi ed by sandstone in the Flinders Ranges of South Aus- and probably in a euxinic environment (Li et Ediacaran pedogenesis and that Ediacara fossils tralia, the Miaohe Member (or Member IV) al., 2010). Abundant macroalgae and putative are lichens or microbial consortia that lived on black shale in the Yangtze Gorges area (China), animals are preserved as carbonaceous compres- paleosols; i.e., the terrestrial Ediacara hypoth- and the lower Lantian Formation (or Member sions on bedding surfaces of Miaohe black shale esis (Retallack, 1994, 2012, 2013). If true, this II) black shale in southern Anhui (South China; in the Yangtze Gorges area and equivalent strata reinterpretation would radically modify our view Fig. DR1 in the GSA Data Repository1). at Wenghui in Guizhou Province (Figs. DR1 and about early animal evolution, biological terres- The Ediacara Member of the Rawnsley DR3) (Xiao et al., 2002; Zhao et al., 2004; Zhu et trialization, chemical weathering, and elemental Quartzite is probably 560–550 Ma based on its al., 2008). Some of the macroalgae have differ- cycling in the Ediacaran Period. However, the paleontological similarity to the dated Ediacaran entiated rhizoidal structures and a dichotomous sedimentological evidence marshaled in sup- succession in the White Sea area (Lafl amme et branching system up to 15 cm in height, but port of a paleosol interpretation for the Ediacara al., 2013). The Rawnsley Quartzite is the young- there is no evidence for vascular structures pro- Member is ambiguous (Callow et al., 2013; Xiao est part of the Ediacaran Wilpena Group, which viding mechanical support and nutrient transport and Knauth, 2013), and many Ediacara forms represents a succession deposited during an in- that would allow a terrestrial lifestyle. Therefore, have characteristic animal features such as bi- terval of postglacial marine transgression (Preiss, they were likely marine benthic organisms that lateral symmetry and self-powered locomotion 1987). The Ediacara Member fi lls an erosional lived in the photic zone. Their superb preserva- (Gehling et al., 2005; Ivantsov, 2009). Here we disconformity cut into the intertidal sandstone tion indicates that they could not have been up- use comparative paleobiological and functional facies of the underlying Chace Quartzite Mem- rooted from terrestrial environments and trans- morphological evidence to further evaluate this ber of the Rawnsley Quartzite and the Bonney ported over long distances, an inference that is hypothesis. The rationale of our approach is Sandstone, and occurs 50–500 m below a basal also consistent with the random orientation of al- simple: terrestrial organisms must show func- Cambrian disconformity (Gehling, 1999). It is gal fossils and the lack of sedimentary evidence tional morphological adaptions to address spe- from 5 to 150 m thick at basin margins, and has for wave or current activities. Instead, the Miao- cifi c challenges in a terrestrial environment. Be- he fossils were either preserved in situ or drifted cause marine and terrestrial environments differ 1GSA Data Repository item 2013304, geological intrabasinally to a localized euxinic environment drastically, organisms adapted to these environ- setting, sedimentary structures, and additional fossils, for preservation (Xiao et al., 2002). is available online at www.geosociety.org/pubs/ft2013 ments are expected to have different functional .htm, or on request from [email protected] or The 35-m-thick Member II black shale of morphology, physiology, and ecology. Conse- Documents Secretary, GSA, P.O. Box 9140, Boulder, the lower Lantian Formation in southern Anhui quently, if Ediacara fossils have morphological CO 80301, USA. overlies basal Ediacaran cap dolostone (Member

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I), and correlation with the Doushantuo Forma- tion in the Yangtze Gorges area suggests a depo- sitional age of 635−580 Ma (Yuan et al., 2011). The fossiliferous black shale is fi nely laminated (Fig. DR4) and pyrite rich, and was probably deposited in largely anoxic, quiet offshore en- vironments (Shen et al., 2008). Macrofossils from this unit include benthic macroalgae and problematic organisms with putative metazoan affi nities (Yuan et al., 2011). Like the Miaohe fossils, exceptional preservation and random fossil alignment demonstrate that the Lantian macrofossils were not transported from a ter- restrial environment; instead, they were either preserved in situ or drifted intrabasinally over short distances (Yuan et al., 2011). There is absolutely no evidence for paleosol development in the Miaohe and Lantian black shales. These black shales were deposited be- low the storm wave base, and there is no sedi- mentological evidence for subaerial exposures (Xiao et al., 2002; Yuan et al., 2011). Further- more, the fi ne lamination and enrichment in or- ganic carbon (to 8% in Miaohe and to 15% in Lantian) and pyrite (>5% in Miaohe) in these black shales are inconsistent with paleosol de- velopment (McFadden et al., 2008), because pedogenic processes would have disrupted the fi ne lamination, and organic carbon and pyrite would have been oxidized, given the oxygen levels in Ediacaran atmospheres (Canfi eld et al., 2007). Thus, comparative paleobiology between the Ediacara Member and the Miaohe and Lan- tian black shales offers an excellent opportunity to test the terrestrial Ediacara hypothesis.

COMPARATIVE PALEOBIOLOGY AND FUNCTIONAL MORPHOLOGY Zhu et al. (2008) reported Eoandromeda oc- tobrachiata, a benthic diploblastic grade animal, from the sheet-fl ow sand facies of the Ediacara Member, Miaohe black shale in the Yangtze Gorges area, and uppermost Doushantuo black shale at Wenghui. E. octobrachiata is an easily Figure 1. A: Eoandromeda octobrachiata from uppermost Doushantuo black shale at recognizable form characterized by eight spiral Wenghui (China). B: E. octobrachiata from Ediacara Member sandstone (South Aus- arms that have transverse markings (Figs. 1A and tralia). C–F: Flabelophyton lantianensis from black shale of lower Lantian Formation 1B). The common occurrence of this species in (South China). G, H: Similar forms from Ediacara Member sandstone. Arrowheads point to globose holdfasts, and arrows point to organic mass at base. Black scale the three Ediacaran successions, including two bars = 5 mm, white scale bars = 1 cm. units of black shale without any evidence for Ediacaran pedogenesis, provides evidence that suggests that all three are marine successions. 0.05–0.2 mm (Yuan et al., 2011). The Ediacara However, the functional and morphological dif- Our recent investigation shows that addi- specimens (Figs. 1G–1H; to 250 mm in height, ferentiation into a holdfast, a globose structure, tional forms are shared between the Ediacara 50 mm in maximum width, and 0.5–1 mm in a stipe, and a bundle of fi laments indicates that Member in South Australia and Ediacaran black fi lament thickness) are larger and have a thin- Flabelophyton is likely an erect benthic eukary- shales in South China, including Flabelophyton, ner stipe than the Lantian specimens, but they ote with pseudoparenchymatous thalli. This Gesinella, Liulingjitaenia, Longifuniculum, and share the basic morphological differentiation degree of functional and morphological differ- Beltanelliformis. Flabelophyton from the lower into a globose holdfast, a stipe, and a bundle of entiation is comparable to the macroalga Baculi- Lantian Formation (Figs. 1C–1F) is character- fi laments. Anchored specimens are sometimes phyca taeniata from the Miaohe biota, although ized by a globose holdfast (sometimes with oriented by currents, consistent with deposi- B. taeniata is characterized by truly parenchy- additional organic mass at base), a stipe, and a tion in a subaqueous environment. Aggregated matous stipe and blade (Xiao et al., 2002). The bundle of fi laments, with an overall height of fi laments are common features among modern functional morphology of Flabelophyton-like 10–50 mm, maximum width of 4–20 mm, diver- cyanobacteria and Miaohe fossils interpreted as forms from the Ediacara Member is consistent gence angle of 5°–50°, and fi lament thickness of cyanobacteria (Steiner, 1994; Xiao et al., 2002). with a subaqueous life mode but inconsistent

2 www.gsapubs.org | October 2013 | GEOLOGY Geology, published online on 30 July 2013 as doi:10.1130/G34691.1 with a terrestrial one, because its thin stipe con- terrestrial lifestyle, and its fl exible tube walls 1994). It is characterized by bundled fi laments sisting of fi ne fi laments and lacking vascular and the lack of any mechanical reinforcement that form structures centimeter to decimeter in structures does not provide suffi cient mechanic are inconsistent with a terrestrial life mode. length (Fig. 2D). Unlike Flabelophyton, Lon- support for an organism as much as 250 mm in Liulingjitaenia and Longifuniculum provide gifuniculum lacks specialized holdfast or stipe, height to stand erect in a terrestrial environment. additional examples of shared taxa between the and its extremely thin fi laments (0.05 mm) are The Ediacara Member also contains forms Ediacara and Miaohe Members. Liulingjitaenia very fl exible and tend to fl are toward one or both that are similar to Gesinella. This genus was from the Miaohe biota was reconstructed as a ends of the bundle (Xiao et al., 2002). Longifunic- originally described from organic-rich mud- long tubular organism characterized by helical ulum-like forms from the Ediacara Member can stone of the late Ediacaran Liuchapo Formation plicate folds or thickenings (Xiao et al., 2002), also be decimeter in size, and consist of fi laments in northern Hunan, South China (Steiner, 1994), although as more specimens become available that fl are at both ends (Figs. 2E and 2F). From but later found in the uppermost Doushantuo it now seems more likely that it consists of a functional morphology point of view, Longifu- black shale at Wenghui (Fig. 2A; Zhao et al., helically twisted fi laments, which can be un- niculum was unable to survive in a terrestrial en- 2004). It is reconstructed as a siphonous alga, twisted, straightened, and loosened (Fig. 2G). vironment, because its fl ared, unprotected, and with a tubular to spindle-shaped thallus that This genus has also been reported from the up- extremely thin fi laments have large surface area reaches to 90 mm in height and 30 mm in maxi- permost Doushantuo black shale at Wenghui to volume ratios and pose fundamental physi- mum width. The best preserved specimens have (Zhao et al., 2004) and the late Ediacaran bitu- ological problems for terrestrial life (Boyce, a holdfast, indicating an erect benthic lifestyle minous limestone of the Khatyspyt Formation 2008). These problems are related to desicca- (Steiner, 1994). The Ediacara specimens are of in Siberia (Grazhdankin et al., 2008). Similar tion, mechanical support, nutrient transport, comparable size and morphology (Figs. 2B and forms from the Ediacara Member clearly show and photosynthesis. They become even more 2C). Even though they are preserved as casts the fi lamentous nature, as well as twisted fi la- acute if fossiliferous Ediacara beds are inter- and molds in much coarser sediments than the ments at one end and loosened fi laments at the preted as dry soils in an arid environment (Re- Liuchapo and Doushantuo Formations, their other (Fig. 2H). tallack, 2013). However, a large surface area to tubular nature is evident from the deformed Longifuniculum has been previously known volume ratio would be a natural adaptation for tube walls with plicate folds (Fig. 2C). Gesi- from black shales of the Miaohe Member (Xiao nutrient absorption in an aquatic environment nella shows no morphological adaptations to et al., 2002) and Liuchapo Formation (Steiner, (Lafl amme et al., 2009).

Figure 2. A: Gesinella hunanensis from uppermost Doushantuo black shale at Wenghui (China; courtesy of Y. Zhao). B, C: Similar tubular forms from Ediacara Member (South Australia) sandstone. D: Longifuniculum dissolutum from Miaohe Member black shale in Yangtze Gorges (China) area (courtesy of M. Steiner). E, F: Similar forms from Ediacara Member sandstone. G: Liulingjitaenia alloplecta from Miaohe Member black shale in Yangtze Gorges area. H: Similar form from Ediacara Member sandstone. Arrowheads (in D–H) point to twisted and tightened fi laments, and arrows point to loosened and fl aring fi laments. I: Beltanelliformis from Miaohe Member. J, K: Beltanelliformis from Ediacara Member. Arrowheads point to Helminthoidichnites traces cutting Beltanelliformis fossils preserved on sole bedding surface. Black scale bars = 5 mm (unless otherwise noted) and white scale bars = 1 cm.

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Beltanelliformis provides another example of the Ediacara Member and other marine succes- or Cheshire Cat?: Gondwana Research, v. 23, shared taxa between the Miaohe and Ediacara sions implies that the Ediacara biota is of ma- p. 558–573, doi:10.1016/j.gr.2012.11.004. Members (Figs. 2I−2K). It consists of aggregat- rine origin; and (4) some of the Ediacara fossils Li, C., Love, G.D., Lyons, T.W., Fike, D.A., Ses- sions, A.L., and Chu, X., 2010, A stratifi ed re- ed discoidal structures millimeters to centime- discussed here are not morphologically adapted dox model for the Ediacaran ocean: Science, ters in diameter, and could represent collapsed to address critical challenges for a terrestrial life v. 328, p. 80–83, doi:10.1126/science.1182369. spherical organisms that are preserved as car- mode. Thus, published sedimentological evi- McFadden, K.A., Huang, J., Chu, X., Jiang, G., bonaceous compressions in Miaohe black shale dence for pedogenesis in the Ediacara Member Kaufman, A.J., Zhou, C., Yuan, X., and Xiao, S., 2008, Pulsed oxygenation and biological evolu- (Xiao et al., 2002) or as three-dimensional casts needs to be reevaluated critically. tion in the Ediacaran Doushantuo Formation: Na- and molds in Ediacaran sandstones of South tional Academy of Sciences Proceedings, v. 105, Australia and elsewhere (Narbonne and Hof- ACKNOWLEDGMENTS p. 3197–3202, doi:10.1073/pnas.0708336105. This work was supported by the U.S. National Sci- Narbonne, G.M., 2005, The Ediacara Biota: Neopro- mann, 1987). It is important that Ediacara Belta- ence Foundation, the Chinese Academy of Sciences, nelliformis specimens preserved in sole bedding terozoic origin of animals and their ecosystems: the Australian Research Council Discovery Grant Annual Review of Earth and Planetary Sci- surfaces are cut by Helminthoidichnites traces Program, the National Natural Science Foundation of ences, v. 33, p. 421–442, doi:10.1146/annurev likely produced by undermat burrowing ani- China, the Chinese Ministry of Science and Technol- .earth.33.092203.122519. mals. Retallack (2013) interpreted such traces ogy, and the NASA Exobiology and Evolutionary Biol- Narbonne, G.M., and Hofmann, H.J., 1987, Ediacaran ogy Program. D. Erwin, M. Lafl amme, and two anony- as slime mold trails. 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