Putting the cart before the horse: An example of how the lack of taphonomical approaches can mislead paleobiological inferences for the late Ediacaran
Introduction
Ediacaran strata offer some of the first evidence for many evolutionary innovations, including the appearance of macroscopic complex biotas (Shen et al., 2008), motility (Ivantsov and Malakhovskaya, 2002, Ivantsov, 2013, Liu and McIlroy, 2015) and skeletonized animals (Penny, 2018). Given the complexity of these scenarios, disregarding the influence of taphonomy when creating taxonomic databases could induce erroneous assumptions regarding species (Lucas, 2001). For example, discoidal organisms from the Ediacaran were first described and differentiated into several different species and genera, likely based on the interpretation that they were impressions of medusa-like animals. As other evidence was considered, it was shown that a number of such discoid forms were holdfast impressions of frondose organisms (with preserved pieces of fronds) (Droser et al., 2006) and that their morphology was, in many cases, related to taphonomic biases (Tarhan et al., 2010, Tarhan et al., 2015). Thus, taphonomy will always be imperative to understanding the taxonomic composition of such important biotas (e.g., Gehling et al., 2000, Grey and Willman, 2009, Liu et al., 2011) and improving our comprehension of paleobiological (Laflamme et al., 2007, Flude and Narbonne, 2008, Elliott et al., 2011, Meyer et al., 2012, Narbonne et al., 2014), geobiological (Mapstone and McIlroy, 2006), and sedimentological processes (Warren et al., 2013).
This is the case for the shelly fossil Cloudina, whose taxonomy is still controversial despite being one of the most geographically widespread and abundant fossils in the latest Ediacaran carbonate rocks (Germs, 1972, Grant, 1990, Conway-Morris et al., 1990, Hofmann and Mountjoy, 2001, Hua et al., 2003, Hua et al., 2005, Cortijo et al., 2010, Kerber et al., 2013, Becker-Kerber and Pacheco, 2018, Adorno et al., 2017). With the exception of recent works (Cortijo et al., 2010, Yang et al., 2016, Cai et al., 2017), most of the species attributed to the genus Cloudina have been distinguished by their external diameters: Cloudina hartmanae Germs, 1972 (2.5–6.5 mm); Cloudina riemkeae Germs, 1972 (0.3–1.3 mm); and Cloudina lucianoi (Beurlen and Sommer, 1957) (0.2–3.8 mm in Zaine and Fairchild, 1987). Other than size, these three species were described by the same diagnostic characteristic: a conico-tubular shell constructed by excentrically nested funnel segments, with concentrically placed circular to ellipsoid layers in cross section (Germs, 1972, Zaine and Fairchild, 1987, Grant, 1990, Hua et al., 2005).
Recently, Cai et al. (2017) proposed a new and emended diagnosis for C. hartmanae and described two new species, C. ningqiangensis and C. xuanjiangpingensis, based on other morphological characteristics (e.g., external ornamentations) considered to be more reliable diagnostic features than size classes (Cai et al., 2017). Particularly for C. hartmanae, the differentiating feature was the presence of oblique and/or transverse annulations.
In this study, we discuss new taphonomic data regarding Cloudina deposits from the Tamengo Formation (Corumbá Group, Brazil) and how taphonomy impacts taxonomic interpretations for this fossil. As already stated, the species C. lucianoi from the Tamengo Formation was previously classified by considering its differentiation from other species by size distribution only (Zaine and Fairchild, 1987). This led some authors to propose Cloudina lucianoi as the senior synonym of C. hartmanae (Adorno et al., 2017; but see discussions in Becker-Kerber and Pacheco, 2018, Adorno et al., 2018), considering the priority of the publication date in Beurlen and Sommer (1957).
However, Tamengo Formation carbonates yielding Cloudina tubes were mostly accumulated in relatively shallow marine environments influenced by storms (e.g., indicated by hummocky bedding and packstones and grainstones consisting of Cloudina bioclasts) and intercalated with occasional, relatively deep-water sediments (e.g., fine pelites with Corumbella remains) (Spangenberg et al., 2013, Pacheco et al., 2015). Thus, it is expected that taphonomic factors (e.g. transporting/reworking) could have impacted their original morphology. To investigate this, we hypothesized that Cloudina deposits containing more tubes with few and incomplete segments in cross section, as well as a higher proportion of mud-filled tubes, represent taphocoenoses that suffered a high degree of fragmentation and transportation. We further hypothesized that diagenetic processes, such as dissolution/recrystallization, can also alter the diagnostic features used in Cloudina taxonomy.
Section snippets
Geologic context
The Corumbá Group is a Neoproterozoic succession from the Mato Grosso do Sul State (Southwest of Brazil) that occurs in the southern portion of the Paraguay Belt (Fig. 1). It is a basin that likely evolved under a rift-to-drift scenario (Alvarenga et al., 2000). The Corumbá Group overlies Marinoan glaciogenic diamictites of the Puga Formation (Alvarenga and Trompette, 1992, Boggiani et al., 2010).
The Corumbá Group has a thickness of approximately 600 m (Gaucher et al., 2003). From the base to
Materials and methods
We examined thin sections (n = 87) already housed (see Supplementary Table 1) at the Paleontological Scientific Collection of the Institute of Geosciences at the University of São Paulo (IGc-USP). Most of this material was collected during earlier studies from outcrops in the cities of Corumbá and Ladário (Zaine and Fairchild, 1985, Zaine and Fairchild, 1987, Zaine, 1991, Meira, 2011): specifically, Porto Sobramil (Saladeiro), the Laginha and Corcal quarries, and the Marina Gattass park
Results
We found that the Corcal and Porto Sobramil assemblages showed significantly higher occurrences of tubes with few segments (1, 2) in cross section compared to the Laginha and MG assemblages (Table 1), while the Laginha and MG samples presented significantly higher occurrences of tubes with more segments (4, 5) than the Corcal and Porto Sobramil samples (Table 1). This pattern appeared to be maintained when we analyzed the ratio of complete/incomplete segments (Fig. 5). For example, the Laginha
Discussion
Our taphonomic parameters suggest that alterations in the original morphology (mainly fragmentation) are higher in the Corcal and Porto Sobramil material than in other localities. This is supported by the predominance of individuals with few segments in cross-section and the additional rarity of specimens with four or more segments in cross-section (Table 1). Furthermore, the higher proportion of tubes with incomplete segments in cross-section (“crescentic fragments” in Grant, 1990) strongly
Conclusions
After identifying several taphonomic and diagenetic processes that have influenced the original morphological information of Cloudina from the Tamengo Formation, we reiterate the need for caution when using specific traits for defining or synonymizing species within the Cloudina genus. Variation in size could mean a number of things: ontogeny, intraspecific differences, depositional bias, etc. Hence, other important characteristics need to be considered when proposing taxonomic definitions for
Acknowledgments
This work was conducted during a master scholarship supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Funding Agency at the University of São Paulo. This work also had assistance from the FAPESP Funding Agency, under the Proc. 2013/17835-8. The authors would like to thank the Brazilian Nanotechnology National Laboratory (LNNano) for providing the facilities used for the SEM investigations (project SEM – 16826 and SEM - 23684), and the helpful assistance of
References (72)
- et al.
Cloudina lucianoi (Beurlen and Sommer, 1957), Tamengo Formation, Ediacaran, Brazil: taxonomy, analysis of stratigraphic distribution and biostratigraphy
Precambr. Res.
(2017) - et al.
Reply to Comment on Adorno et al. (2017) “Cloudina lucianoi (Beurlen & Sommer, 1957), Tamengo Formation, Ediacaran, Brazil: Taxonomy, Analysis of Stratigraphic Distribution and Biostratigraphy
Precambr. Res.
(2018) - et al.
Comment on Adorno, et al. Cloudina lucianoi (Beurlen & Sommer, 1957), Tamengo Formation, Ediacaran, Brazil: taxonomy, analysis of stratigraphic distribution and biostratigraphy
Precambr. Res.
(2018) - et al.
Chemostratigraphy of the Tamengo Formation (Corumbá Group, Brazil): a contribution to the calibration of the Ediacaran carbon-isotope curve
Precambr. Res.
(2010) - et al.
Taxonomy of the late Ediacaran index fossil Cloudina and a new similar taxon from South China
Precambr. Res.
(2017) - et al.
A new species of Cloudina from the terminal Ediacaran of Spain
Precambr. Res.
(2010) - et al.
Assemblage palaeoecology of the Ediacara biota: the unabridged edition?
Palaeogeogr., Palaeoclimatol., Palaeoecol.
(2006) - et al.
Integrated correlation of the Vendian to Cambrian Arroyo del Soldado and Corumbá Groups (Uruguay and Brazil): palaeogeographic, paleoclimatic and palaeobiologic implications
Precambr. Res.
(2003) - et al.
Quasi-static axial compression of thin-walled circular aluminium tubes
Int. J. Mech. Sci.
(2001) - et al.
A section of Vendian in the east of West Siberian Plate (based on data from the Borehole Vostok 3)
Russ. Geol. Geophys.
(2008)
On the inextensional axial collapse of thin PVC conical shells
Int. J. Mech. Sci.
Ediacaran fossil preservation: taphonomy and diagenesis of a discoid biota from the Amadeus Basin, central Australia
Precambr. Res.
Size-frequency distributions and taphonomy of brachiopods: a recent model
Palaeogeogr., Palaeoclimatol., Palaeoecol.
The application of size-frequency distribution and energy flow in paleoecologic analysis: an example using parautochthonous death assemblages from a variable salinity bay
Paleogeogr., Palaeoclimatol., Palaeoecol.
Can shallow- and deep-water chemoautotrophic and heterotrophic communities be discriminated in the fossil record?
Paleogeogr., Palaeoclimatol., Palaeoecol.
Taphonomy and morphology of the Ediacara form genus Aspidella
Precambr. Res.
Transitional Ediacaran-Cambrian small skeletal fossil assemblages from South China and Kazakhstan: implications for chronostratigraphy and metazoan evolution
Precambr. Res.
Província Tocantins, setor Sudoeste
Paraguay and Araguaia belts
Glacially influenced sedimentation in the later Proterozoic of the Paraguay Belt (Mato Grosso, Brazil)
Palaeogeogr., Palaeoclimatol., Palaeoecol.
Extinction of Cloudina and Namacalathus at the Precambrian-Cambrian boundary in Oman
Geology
Ecological interactions in Cloudina from the Ediacaran of Brazil: implications for the rise of animal biomineralization
Sci. Rep.
Observações Estratigráficas E Paleontológicas Sobre OCalcário Corumbá
Boletim da Divisão de Geologia e Mineralogia
Análise estratigráfica da Bacia Corumbá (Neoproterozoico)- Mato Grosso do Sul [in Portuguese, with English abstract]
The role of experiments in investigating the taphonomy of exceptional preservation
Palaeontology
Size-selective transport of shells by birds and its palaeoecological implications
Palaeontology
The early skeletal organism Cloudina: new occurrences from Oman and possibly, China
J. Sci.
The size frequency distribution in palaeoecology: effects of taphonomic processes during formation of molluscan death assemblages in Texas bays
Palaeontology
New evidence on the taphonomic context of the Ediacaran Pteridinium
Acta Palaeontol. Polonica
Taphonomy and ontogeny of a multibranched Ediacaran fossil: Bradgatia from the Avalon Peninsula of Newfoundland
Can. J. Earth Sci.
Litoestratigrafía, bioestratigrafía y correlaciones de las sucesiones sedimentarias del Neoproterozoico-Cámbrico del Cratóndel Rio de la Plata (Uruguay y Argentina) [in Spanish, with English abstract]
Latin Am. J. Sedimentol. Basin Anal.
The first named Ediacaran body fossil, Aspidella terranovica
Palaeontology
New shelly fossils from Nama Group, South West Africa
Am. J. Sci.
Shell structure and distribution of Cloudina, a potential index fossil for the terminal Proterozoic
Am. J. Sci.
Taphonomy of Ediacaran acritarchs from Australia: significance for taxonomy and biostratigraphy
Palaios
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Assessing the correlation between Ediacaran-Cambrian units of SW Gondwana: The Tagatiya Guazú (Itapucumi Group, Paraguay) and Tamengo (Corumbá Group, Brazil) formations
2023, Journal of South American Earth SciencesEdiacaran ramp depositional model of the Tamengo Formation, Brazil
2019, Journal of South American Earth SciencesCitation Excerpt :According to the authors, this glacial event would be younger than the Gaskiers glaciation, and would correlate in part with the Shuram-Wonoka isotopic anomaly. There exists a prolific debate regarding taxonomic affinities of the Cloudina genus in the four decades of its study (Germs, 1972; Zaine and Fairchild, 1987; Grant, 1990; Conway Morris et al., 1990; Conway-Morris, 1993; Hua et al., 2003, 2005; Adorno et al., 2017), including morphology (Grant, 1990; Seilacher, 1999; Adorno et al., 2017; Mehra and Maloof, 2018), mineralogy (Grant, 1990; Brain, 2001; Hua et al., 2005; Becker-Kerber et al., 2017), paleoecology (Germs, 1972; Grant, 1990; Seilacher, 1999; Hua et al., 2005; Cortijo et al., 2010; Becker-Kerber et al., 2017; Mehra and Maloof, 2018) taphonomy (Cortijo et al., 2010; Meira, 2011; Warren et al., 2012; Becker-Kerber et al., 2017, 2019; Mehra and Maloof, 2018) and extinction (Brain, 2001; Hua et al., 2003; Becker-Kerber et al., 2017). In contrast, information about the sedimentary environment in which these fossils inhabited are restricted to the Nama Group in Namibia (Germs, 1972; Seilacher, 1999; Grotzinger et al., 2000) and the central region of the Iberian Peninsula (Vidal et al., 1994).
Taxonomic revision of Ediacaran tubular fossils: Cloudina, Sinotubulites and Conotubus
2022, Journal of PaleontologyDiscovery of bilaterian-type through-guts in cloudinomorphs from the terminal Ediacaran Period
2020, Nature Communications