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BOAG ET AL.
be argued for the absence of many White Sea taxa in older, deep-water Avalonian strata. Overall, these paleoenvironmental attributes are in opposition to the core requirements of index fossils, potentially lessening the strength for either of the Avalonian or White Sea assemblages to be used as discrete faunal stages to demarcate Ediacaran biostratigraphy. The Nama Assemblage (549–541 Ma), mean-
while, appears to be a unique faunal stage in the terminal Ediacaran, defined by a global loss of diversity, coincident with the survival of bathymetrically unrestricted, long-ranging Ediacara-type taxa. In an extinction scenario, ecological theory predicts surviving faunal communities should be composed of generalist taxa with broad niche tolerances (Darroch et al. 2015); this appears to be directly reflected by database results. These remaining biota are coeval with the globally occurring, mineralized taxon Cloudina. Easily recognizable and distributed in carbonate stratigraphy world- wide, it appears to be an excellent index fossil candidate for a terminal Ediacaran stage–level subdivision, indicative of a globally correlative biozone ca. 549–541 Ma. The final establish- ment of a robust Ediacaran biostratigraphy is one step that will ultimately allow for temporal integration of fossil, biological, and environ- mental records to assess macroevolutionary patterns on the eve of the Cambrian radiation.
Acknowledgments We thank P.Wagner and E. Sperling for their
helpful discussion and comments. T.H.B. was supported by the University of Toronto,MaryH. Beatty Fellowship, and National Sciences and EngineeringResearchCouncil ofCanada–Canada Graduate Scholarship-Master’s; S.A.F.D. thanks the Smithsonian National Museum of Natural History for financial support; and M.L. thanks the Connaught Foundation, National Sciences and Engineering Research Council of Canada, and National Geographic Society for generous funding.
Literature Cited
Amthor, J. E., J. P. Grotzinger, S. Schröder, S. A. Bowring, J. Ramezani, M. W. Martin, and A. Matter. 2003. Extinction of Cloudina and Namacalathus at the Precambrian–Cambrian boundary in Oman. Geology 31(5):431–434.
Babcock, L. E., A. M. Grunow, G. R. Sadowski, and S. A. Leslie. 2005. Corumbella, an Ediacaran-grade organism from the Late Neoproterozoic of Brazil. Palaeogeography, Palaeoclimatology, Palaeoecology 220:7–18.
Baselga, A. 2010. Partitioning the turnover and nestedness com- ponents of beta diversity. Global Ecology and Biogeography 19:134–143.
Baselga, A., andD.L.Orme. 2012. Betapart: anRpackage for the study of beta diversity. Methods in Ecology and Evolution 3:808–812. Bengston, S. M., and Y. Zhao. 1992. Predatorial borings in late Precambrian mineralized exoskeletons. Science 257:367–369.
Benus, A. P. 1988. Sedimentological context of a deep-water Ediacaran fauna (Mistaken Point, Avalon Zone, eastern Newfoundland). In E. Landing, G. M. Narbonne, and P. M. Myrow eds. Trace fossils, small shelly fossils and the Precambrian–Cambrian
boundary.NewYork State Museum and Geophysical Survey Bulletin 463:8–9. Billings, E. 1872. Fossils in Huronian rocks. Canadian Naturalist and Quarterly Journal of Science 6:478.
Bosak, T., D. J. G. Lahr, S. B. Pruss, F.
A.Macdonald, A. J. Gooday, L. Dalton, and
E.D.Matys. 2012. Possible early Foraminiferans in post-Sturtian (716–635 Ma) cap carbonates. Geology 40(1):67–70.
Bouougri, E. H., and H. Porada. 2007. Siliciclastic biolaminites indicative of widespread microbial mats in the Neoproterozoic Nama Group of Namibia. Journal of African Earth Sciences 48:38–48.
Bouougri, E. H., H. Porada, K. Weber, and J. Reitner. 2011. Sedi- mentology and palaeoecology of Ernietta-bearing Ediacaran deposits in southern Namibia: implications for infaunal vendo- biont communities. Advances in Stromatolite Geobiology: Lecture Notes in Earth Sciences 313:473–506.
Bowring, S. A., J. P. Grotzinger, C. E. Isachsen, A. H. Knoll, S. Pelechaty, and P. Kolosov. 1993. Calibrating rates of early Cambrian evolution. Science 261:1293–1298.
Boynton,H. E., and T. D. Ford. 1979. Pseudovendia charnwoodensis— a new Precambrian arthropod from Charnwood Forest, Leicestershire. Mercian Geologist 7:175–177.
——. 1995. Ediacaran fossils from the Precambrian (Charnian Supergroup) of Charnwood Forest, Leicestershire, England. Mercian Geologist 13:165–182.
——. 1996. Ediacaran fossils from the Precambrian (Charnian Supergroup) of Charnwood Forest, Leicestershire, England— revision of
nomenclature.Mercian Geologist 14:3.
Brasier, M. D.,G. Shields, V. N. Kuleshov, and E.A. Zhegallo. 1996. Integrated chemo- and biostratigraphic calibration of early animal evolution: Neoproterozoic–early Cambrian of southwest Mongolia. Geological Magazine 133(4):445–485.
Brasier, M. D., J. B. Antcliffe, andR.H.
T.Callow. 2010. Evolutionary trends in remarkable fossil preservation across the Ediacaran– Cambrian transition and the impact of metazoan mixing. In P. A. Allison and D. J. Bottjer, eds. Taphonomy: process and bias through time. Aims and Scope Topics in Geobiology 32:519–567.
Brasier, M. D., J. B. Antcliffe, andA.G. Liu. 2012. The architecture of Ediacaran fronds. Palaeontology 55:1105–1124.
Briggs, D. E. G. 2003. The role of decay and mineralization in the preservation of soft bodied fossils. Annual Review of Earth and Planetary Sciences 31:275–301.
Budd, G. E., and S. Jensen. 2015. The origin of the animals and a “Savannah” hypothesis for early bilaterian evolution. Biological Reviews. doi: 10.1111/brv.12239.
Burzynski, G., and G. M. Narbonne. 2015. The discs of Avalon: relating discoid fossils to frondose organisms in the Ediacaran of Newfoundland, Canada. Palaeogeography, Palaeoclimatology, Palaeoecology 434:34–45.
Cai, Y., J. D. Schiffbauer, H. Hua, and S. Xiao. 2012. Preservational modes in the Ediacaran Gaojiashan Lagerstätte: pyritization,
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