A new Burgess Shale-type deposit from the Ediacaran of western Mongolia.

Stephen Q Dornbos,Akihiro Kanayama,Sersmaa Gonchigdorj,Tatsuo Oji

doi:10.1038/srep23438

Abstract

Preservation of soft-bodied organisms is exceedingly rare in the fossil record. One way that such fossils are preserved is as carbonaceous compressions in fined-grained marine sedimentary rocks. These deposits of exceptional preservation are known as Burgess Shale-type (BST) deposits. During the Cambrian Period, BST deposits are more common and provide a crucial view of early animal evolution. The earliest definitive fossil evidence for macroscopic animal-grade organisms is found in the preceding Ediacaran Period. BST deposits from the Ediacaran are rarer and lack conclusive evidence for animals. Here we report the discovery of a new Ediacaran BST deposit with exceptional preservation of non-mineralizing macro-organisms in thinly bedded black shale from Zavkhan Province, western Mongolia. This fossil assemblage, here named the Zuun-Arts biota, currently consists of two new species of probable macroscopic multicellular benthic algae. One species, Chinggiskhaania bifurcata n. gen., n. sp., dominates the biota. The other species, Zuunartsphyton delicatum n. gen., n. sp., is known from three specimens. SEM-EDS analysis shows that the fossils are composed of aluminosilicate clay minerals and some carbon, a composition comparable to fossils from the Cambrian Burgess Shale biota. This discovery opens a new window through which to view late Precambrian life.

Highlights

Ediacaran Burgess Shale-type (BST) deposits are known from several localities around the globe, including Siberia[1], India[2], Paraguay[3], the western United States[4], the Yangtze Platform of South China[5,6], and various upper Ediacaran deposits containing the multicellular benthic alga Vendotaenia[7,8]
The fossils are preserved in a thinly bedded black shale facies that is slightly less than 7 m thick (Fig. 1)
The fossiliferous zone is in strata from 40 cm to 80 cm within the black shale (Fig. 1)

Summary

Introduction

Ediacaran BST deposits are known from several localities around the globe, including Siberia[1], India[2], Paraguay[3], the western United States[4], the Yangtze Platform of South China[5,6], and various upper Ediacaran deposits containing the multicellular benthic alga Vendotaenia[7,8]. The most diverse of these assemblages are the two from the Yangtze Platform of South China, the Lantian and Miaohe biotas[5,6] They both contain mostly benthic multicellular eukaryotic algae fossils preserved as carbonaceous compressions in fine-grained marine shales[5,6,9,10]. The regional Ediacaran–Cambrian boundary is placed near the top of the Zuun-Arts Formation based on a large negative carbon isotope excursion[14] and the first appearance of the penetrative trace fossil Treptichnus pedum in the overlying Bayan Gol Formation[14,15]

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Conclusion