New observations of the ornamented Doushantuo embryo fossils from the Ediacaran Weng’an Biota, South China

Abstract

Phosphatized Weng'an embryo fossils from the Ediacaran Doushantuo Formation in Guizhou, South China are dominated by various ornamented spheroidal fossils, with one internal body or several blastomeres enclosed within a single or multiple layered envelope, which have been interpreted as the resting eggs or diapause embryos of metazoans. Based on the microstructure of the envelope, we separated these ornamented spheroidal fossils into two groups: 1) group one, represented by typical Megasphaera ornata and characterized by an envelope consisting of at least two thick capsules with various surface ornaments and a single internal body, which can be interpreted as resting eggs; 2) another group, exhibiting an envelope consisting of a thin capsule with cell-like surface structure and internal blastomeres (amount is equal to 2 n , n = 0, 1, 2, 3…), which are probably not diapause embryos but developing blastulae at various holoblastic cleavage stages.•

Experimental precipitation of apatite pseudofossils resembling fossil embryos

“…However, some of our precipitates are comparable in size to some large Doushantuo microfossils (e.g., Figure ). Additionally, the sizes of globular Doushantuo microfossils themselves range from <100 μm in diameter to over 1,000 μm in diameter (Chi, ; figures 5 & 6; Muscente, Hawkins, & Xiao, ; figure b,h,i), and the size of the textures associated with them exhibit a broad size range that overlaps on the small end with the range of abiotic precipitates observed in our experiments (Yin & Zhu, ; compare Figure a–e and Figure c–g). Whether or not slower precipitation, or alternative chemical environments in natural systems, would produce features as large as the largest precipitates interpreted as embryos and embryo‐ornamentation in the fossil record remains an open question.…”

“…However, some of our precipitates are comparable in size to some large Doushantuo microfossils (e.g., Figure 3). Additionally, the sizes of globular Doushantuo microfossils themselves range from <100 μm in diameter to over 1,000 μm in diameter (Chi, 2009;figures 5 & 6;Muscente, Hawkins, & Xiao, 2015;figure 5b,h,i), and the size of the textures associated with them exhibit a broad size range that overlaps on the small end with the range of abiotic precipitates observed in our experiments (Yin & Zhu, 2012; compare The chemical environment that resulted in these precipitates is a plausible simulant of modern microenvironments that host active phosphogenesis. Although marine waters are generally not supersaturated with respect to apatite, certain conditions lead to a dispersed "background" precipitation of apatite extending across continental margins generally (Ruttenberg & Berner, 1993).…”

“…Microfossil features not observed in our pseudofossils: (a) Ornamented envelope, separate from, but encasing, apparent discontinuous blastomeres (Yin & Zhu, ); (b) internal filaments interpreted as organic (Xiao & Knoll, ); (c) matryoshkas (arrows) (Chen et al., ); (d) acanthomorphic acritarch (Yin et al., ); and (e) early Cambrian lobed embryo (Steiner, Qian, Li, Hagadorn, & Zhu, ); scale bars: 100 μm…”

“…(a) Experimentally produced bowl-shaped precipitates, similar to collapsed cells, a′ (Westall & Folk, 2003); (b) multisphere precipitate similar to ornamented sphere b′ (Sugitani et al, 2015). Scale bars: a, b′: 10 μm; a′: 1 μm; b: 100 μm F I G U R E 5 Microfossil features not observed in our pseudofossils: (a) Ornamented envelope, separate from, but encasing, apparent discontinuous blastomeres (Yin & Zhu, 2012); (b) internal filaments interpreted as organic (Xiao & Knoll, 1999); (c) matryoshkas (arrows) (Chen et al, 2014); (d) acanthomorphic acritarch (Yin et al, 2007); and (e) early Cambrian lobed embryo (Steiner, Qian, Li, Hagadorn, & Zhu, 2014); scale bars: 100 μm…”

The Precambrian-Cambrian biosphere (r)evolution: Insights from the Chinese Yangtze Platform

“…Xiao et al 1998, Yin et al 2012but see Huldtgren et al 2011), diverse acritarch assemblages (Liu et al 2012b), and the unique macro-fossils from the latest Ediacaran siliciclastic shelf deposits of Gaojiashan, southern Shaanxi Province (e.g. Hua et al 2009).…”