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mega-biases (Narbonne 2005), or a superposi- tion of both time and ecology (Narbonne et al. 2014). It is important to note that despite the hypothesized impact of these variables on Ediacaran taxonomic diversity, they have so far been demonstrated to share little correlation with overallpatterns inmorphospaceamong the Ediacara-type biota (Shen et al. 2008). Here, we present findings from a new,
global-scale meta-analysis of the Ediacaran macrofossil record. Using an updated paleonto- logical database that serves as a platform for robust statistical evaluation, we test: (1) the validity of contemporary Ediacaran biotic assemblages as discrete taxonomic groupings; and, (2) the statistical significance of temporal, paleoenvironmental, and lithological factors that may control the observed distribution of taxa in the Ediacaran fossil record at a global scale. Testing the extent to which the Avalon, White Sea, and Nama assemblages represent successive stages in Ediacaran evolution, or instead environmental or taphonomic hetero- geneities, is crucial for the development of a robust biostratigraphy for the Neoproterozoic era. Furthermore, a revised biostratigraphy is critical to permit temporally accurate correlative testing of causal drivers for early metazoan diversification—including ecological (Laflamme et al. 2013; Darroch et al. 2015), developmental (Erwin et al. 2011), and environ- mental (Sperling et al. 2013; Lyons et al. 2014) changes under way in the latest Ediacaran stratigraphy worldwide.
Methods
Paleontological Database Parameters An Ediacaran paleontological database was
constructed as a data matrix with localities being defined on the basis of geographic location (i.e., unique latitude and longitude coordinates). When multiple fossil horizons co- occurred in a single continuous stratigraphic package, additional localities were subdivided based on stratigraphic distribution. Localities were coded for the following “characters” using published primary literature: modern locality coordinates, geological unit of occur- rence, geochronological age constraint(s),
depositional environment and approximate water depth, fossil-preserving lithology, bedding-plane sedimentary structures, dia- genetic minerals and processes associated with preservation, taxonomy (and abundance when present—to generic and/or species level when available), associated bioturbation index and ichnotaxa, and finally, historical literature published on the locality of interest. From this parent database, we restricted
the study to localities with more than one taxonomic occurrence, resulting in a subsidiary binary data matrix of 86 Ediacaran localities containing macrofossils (denoted by locality codes in [brackets] hereafter—see Table 1). Importantly, we follow the interpretation that “holdfasts” or “disks” represent the anchoring structure of a frondose organism. As these cannot yet be correlated with any one specific taxon (Burzynski and Narbonne 2015; Tarhan et al. 2015), we did not include Aspidella Billings, 1872, and its associated junior synonyms (see Gehling et al. 2000; Supplemen- tary Table S.1). In addition, we did not include the taxonomically invalid ivesheadiomorphs Pseudovendia Boynton and Ford, 1979, Black- brookia and Shepshedia Boynton and Ford, 1995, and Ivesheadia Boynton and Ford, 1996, as they represent either microbially induced sedimen- tary structures (MISS) (Laflamme et al. 2011b) or taphomorphs of frondose organisms in various states of decomposition prior to preservation (Liu et al. 2011). Each locality was then coded for the presence or absence of 124 remaining Ediacara-type biota, macro- algae, and tubular and mineralizing genera. This diversity catalogue was then investigated with the following treatments taken from the database to be tested against this taxonomic distribution to evaluate their validity: (1) temporal binning into the three informally assigned Ediacaran biostratigraphic stages (Avalon, 579–559 Ma; White Sea, 558–550Ma; and Nama, 549–541Ma; Narbonne et al. 2012), (2) paleoenvironmental setting and water depth, and (3) preserving facies (lithology), to visualize trends observed in previous studies at a global scale (Supplementary Tables S.2, S.6, and database references therein; Waggoner 2003; Grazhdankin 2004, 2014; Narbonne 2005; Gehling and Droser 2013).
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