Complex embryos displaying bilaterian characters from Precambrian Doushantuo phosphate deposits, Weng'an, Guizhou, China

Chen, Jun-Yuan; Bottjer, David J.; Li, Gang; Hadfield, Michael G.; Gao, Feng; Cameron, R. Andrew; Zhang, Chenyu; Xian, Dingchang; Tafforeau, Paul; Liao, Xin; Yin, Zongjun

doi:10.1073/pnas.0904805106

Cited by 63 publications

(37 citation statements)

References 21 publications

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“…Despite our differences, Xiao and colleagues are in close agreement with our general conclusions. This contrasts with common interpretations of the Doushantuo fossils as advanced metazoans [e.g., (16,(22)(23)(24)]. …”

contrasting

confidence: 81%

Response to Comment on “Fossilized Nuclei and Germination Structures Identify Ediacaran ‘Animal Embryos’ as Encysting Protists”

Huldtgren

Cunningham

Yin

et al. 2012

Science

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The objections of Xiao et al. to our reinterpretation are based on incorrect assumptions. The lack of nanocrystals lining the nuclear membrane is consistent with membrane fossilization, and nucleus volume through development is correlated to cytoplasm volume and fully consistent with sizes of eukaryote nuclei. Identical envelope structure unites the developmental stages of the fossils, and 2 n cleavage and Y-shaped junctions are holozoan symplesiomorphies.X iao et al.(1) claim that our reassessment (2) of previously interpreted "animal embryos" (3) rests on two flawed interpretations: The structures we identify as nuclei are not nuclei, and the proposed life cycle conflates two distinct organisms. Both claims are flawed.We identified the nuclei based on a number of morphological features involving recurrence, position within cells, shape, volumetric relationship between nuclei and cells, and evidence of mitotic division. In all these features, the structures conform to typical cell nuclei. We interpreted the taphonomic history to involve shrinkage of nucleoplasm, leaving a major part of the original nucleus volume molded by diagenetic voidfilling apatite and the nucleoplasm forming a smaller globular body. Xiao et al. do not question our observations or our taphonomic analysis. A recent study (4) by two of the co-authors of Xiao et al.

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contrasting

confidence: 81%

Response to Comment on “Fossilized Nuclei and Germination Structures Identify Ediacaran ‘Animal Embryos’ as Encysting Protists”

Huldtgren

Cunningham

Yin

et al. 2012

Science

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“…These include specimens purported to preserve endodermal cords (J. Chen et al 2009b), polar lobes (J. Chen et al 2006Chen et al , 2009aYin et al 2013), embryonic polarity (J.…”

Section: Bilaterians or Eumetazoans?mentioning

confidence: 99%

The Weng'an Biota (Doushantuo Formation): an Ediacaran window on soft-bodied and multicellular microorganisms

Cunningham

Vargas

Yin

et al. 2017

JGS

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The Weng'an Biota is a fossil Konservat-Lagerstätte in South China that is c. 570 – 609 myr old and provides an unparalleled snapshot of marine life during the interval in which molecular clocks estimate that animal clades were diversifying. It yields fossils that are three-dimensionally preserved in calcium phosphate with cellular and sometimes subcellular fidelity. The biota includes candidates for the oldest animals in the fossil record, including embryonic, larval and adult forms. We argue that, although the Weng'an Biota includes forms that could be animals, none can currently be assigned to this group with confidence. Nonetheless, the biota offers a rare and valuable window on the evolution of multicellular and soft-bodied organisms in the prelude to the Cambrian radiation.

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“…The earliest reported fossils of possible metazoan embryos and adults are in the Ediacaran Doushantuo Formation (∼570 Mya) in southern China (3)(4)(5). Small globular fossils, ∼200 μm in diameter, show remarkable cellular details and have been interpreted as cnidarian gastrulae and planulae as well as bilaterian gastrulae comparable with living molluscans and echinoderms (4).…”

Section: Fossil Recordmentioning

confidence: 99%

Evolution of centralized nervous systems: Two schools of evolutionary thought

2012

Proc. Natl. Acad. Sci. U.S.A.

110

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Understanding the evolution of centralized nervous systems requires an understanding of metazoan phylogenetic interrelationships, their fossil record, the variation in their cephalic neural characters, and the development of these characters. Each of these topics involves comparative approaches, and both cladistic and phenetic methodologies have been applied. Our understanding of metazoan phylogeny has increased greatly with the cladistic analysis of molecular data, and relaxed molecular clocks generally date the origin of bilaterians at 600-700 Mya (during the Ediacaran). Although the taxonomic affinities of the Ediacaran biota remain uncertain, a conservative interpretation suggests that a number of these taxa form clades that are closely related, if not stem clades of bilaterian crown clades. Analysis of brain-body complexity among extant bilaterians indicates that diffuse nerve nets and possibly, ganglionated cephalic neural systems existed in Ediacaran organisms. An outgroup analysis of cephalic neural characters among extant metazoans also indicates that the last common bilaterian ancestor possessed a diffuse nerve plexus and that brains evolved independently at least four times. In contrast, the hypothesis of a tripartite brain, based primarily on phenetic analysis of developmental genetic data, indicates that the brain arose in the last common bilaterian ancestor. Hopefully, this debate will be resolved by cladistic analysis of the genomes of additional taxa and an increased understanding of character identity genetic networks.The fact that some of these building stones are universal does not, of course, mean that the organs to which they contribute are as old as these molecules or their precursors.von Salvini-Plawen and Mayr (1) A ny consideration of the evolution of centralized nervous systems is inextricably linked to an understanding of the phylogeny of living metazoans, their fossil history, the vast range of complexity in their nervous systems, and the development of these nervous systems. For this reason, any attempt to reconstruct the phylogeny of metazoan CNSs must be based on all lines of evidence available. The molecular phylogenetic studies of the last 20 y are particularly important in understanding metazoan interrelationships as well as the time frame in which these animals arose and radiated, and we now have increased insights into the genetics underlying the development of CNSs.First, I will review the fossil history of the earliest putative metazoans, and then, I will discuss different comparative approaches to analyzing both molecular and morphological data: the molecular clock hypothesis, which has yielded a range of possible dates for the origin and divergence of metazoans; developmental genetics and its contribution to our understanding of the patterning of metazoan bodies, particularly patterning of the CNS; and conclusions based on the first outgroup analysis of metazoan central neural characters. Finally, I will review two hypotheses concerning the morphological complexity of the ...

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Complex embryos displaying bilaterian characters from Precambrian Doushantuo phosphate deposits, Weng'an, Guizhou, China

Cited by 63 publications

References 21 publications

Response to Comment on “Fossilized Nuclei and Germination Structures Identify Ediacaran ‘Animal Embryos’ as Encysting Protists”

Response to Comment on “Fossilized Nuclei and Germination Structures Identify Ediacaran ‘Animal Embryos’ as Encysting Protists”

The Weng'an Biota (Doushantuo Formation): an Ediacaran window on soft-bodied and multicellular microorganisms

Evolution of centralized nervous systems: Two schools of evolutionary thought

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