Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China)

Han, Jian; Morris, Simon Conway; Ou, Qiang; Shu, Degan; Huang, Hai

doi:10.1038/nature21072

Cited by 64 publications

(57 citation statements)

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“…The absolute age of this bed is estimated to be about 535 Ma [46,50]. Phosphatic fossils were obtained by digesting rock samples in 8-10% acetic acid [51] followed by picking under a binocular microscope. The most common elements are globular spherical microfossils, specifically olivooids [46,52], metazoan embryos [47], cnidarians [53,54], bacteria [55], possible deuterostomes [51] and problematic fossils [56].…”

Section: Methodsmentioning

confidence: 99%

Origin of ecdysis: fossil evidence from 535-million-year-old scalidophoran worms

et al. 2019

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With millions of extant species, ecdysozoans (Scalidophora, Nematoida and Panarthropoda) constitute a major portion of present-day biodiversity. All ecdysozoans secrete an exoskeletal cuticle which must be moulted periodically and replaced by a larger one. Although moulting (ecdysis) has been recognized in early Palaeozoic panarthropods such as trilobites and basal groups such as anomalocaridids and lobopodians, the fossil record lacks clear evidence of ecdysis in early scalidophorans, largely because of difficulties in recognizing true exuviae. Here, we describe two types of exuviae in microscopic scalidophoran worms from the lowermost Cambrian Kuanchuanpu Formation ( ca 535 Ma) of China and reconstruct their moulting process. These basal scalidophorans moulted in a manner similar to that of extant priapulid worms, extricating themselves smoothly from their old tubular cuticle or turning their exuviae inside out like the finger of a glove. This is the oldest record of moulting in ecdysozoans. We also discuss the origin of ecdysis in the light of recent molecular analyses and the significance of moulting in the early evolution of animals.

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Section: Methodsmentioning

confidence: 99%

Origin of ecdysis: fossil evidence from 535-million-year-old scalidophoran worms

et al. 2019

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“…) and also possible meiobenthic deuterostomes (Han et al . ). These exceptional fossils provide key information on the early stages of animal evolution near the Ediacaran–Cambrian boundary and before the Cambrian Explosion sensu stricto .…”

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Anatomy and affinities of a new 535‐million‐year‐old medusozoan from the Kuanchuanpu Formation, South China

et al. 2017

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We describe here Sinaster petalon gen. et sp. nov., a new embryonic form from the c. 535 million-yearold Kuanchuanpu Formation of South China (Ningqiang, Shaanxi Province). The excellent three-dimensional, phosphatic preservation of these microfossils allowed us to use x-ray microtomographic techniques to make accurate reconstructions of their internal structures and to compare their anatomy point-by-point with that of extant cnidarians and other animal groups. Sinaster petalon has anatomical features typical of extant Medusozoa (Cnidaria), such as coronal muscles, perradial and adradial frenula, interradial septa, accessory septa, gonad-lamellae, tentacle buds and perradial pockets. Although Sinaster cannot be straightforwardly assigned to any crown-group within Medusozoa, the presence of marginal lappets and endodermal lamellae suggests that it is closer to Cubozoa and Scyphozoa than to any other group of modern cnidarians. The tentative placement of Sinaster within the stem-group Cubozoa is justified by the presence of a velarium supported by a frenulum. The cubozoan affinities of Sinaster are also supported by cladistic analysis.

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“…Although meiofaunal burrows (sometimes described as burrow mottling or cryptobioturbation) have occasionally been reported from Cambrian to Recent sediments 26 , they are rarely subjected to detailed study. Body fossil discoveries also reveal organisms inhabiting meiofaunal niches within Early Cambrian communities, highlighting the potential for their preservation within particular taphonomic windows 28,29 .…”

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Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil

et al. 2017

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The evolutionary events during the Ediacaran-Cambrian transition (~541 Myr ago) are unparalleled in Earth history. The fossil record suggests that most extant animal phyla appeared in a geologically brief interval, with the oldest unequivocal bilaterian body fossils found in the Early Cambrian. Molecular clocks and biomarkers provide independent estimates for the timing of animal origins, and both suggest a cryptic Neoproterozoic history for Metazoa that extends considerably beyond the Cambrian fossil record. We report an assemblage of ichnofossils from Ediacaran-Cambrian siltstones in Brazil, alongside U-Pb radioisotopic dates that constrain the age of the oldest specimens to 555-542 Myr. X-ray microtomography reveals three-dimensionally preserved traces ranging from 50 to 600 μ m in diameter, indicative of small-bodied, meiofaunal tracemakers. Burrow morphologies suggest they were created by a nematoid-like organism that used undulating locomotion to move through the sediment. This assemblage demonstrates animal-sediment interactions in the latest Ediacaran period, and provides the oldest known fossil evidence for meiofaunal bilaterians. Our discovery highlights meiofaunal ichnofossils as a hitherto unexplored window for tracking animal evolution in deep time, and reveals that both meiofaunal and macrofaunal bilaterians began to explore infaunal niches during the late Ediacaran. NATuRE ECoLoGy & EvoLuTIoN Articles Nature ecology & evolutioNsupport for these suggestions is limited to purported body fossils of sponges 19 and demosponge biomarkers 20 . A considerable gap therefore remains between the fossil record of the late Ediacaran and molecular clock estimates for deep splits in the animal tree, for example the origin of Metazoa and Eumetazoa 3 . Assuming that contemporary molecular clock analyses yield accurate, if imprecise 18 , node ages for animal divergences, a small body size and concomitant limited fossilization potential 21 could reconcile these discordant records of animal evolution (but see ref. 22 ).The small body size of the ancestral bilaterian is supported by recent phylogenomic analyses of deep animal relationships, with acoel flatworms and xenoturbellids (Xenacoelomorpha) being a sister group to all remaining bilaterians (Nephrozoa) 23 , and smallbodied spiralian taxa (the 'Platyzoa') recognized as a paraphyletic grade with respect to macroscopic trochozoans 24 . This suggests that early bilaterians and spiralians were small bodied, possibly meiofaunal, and moved using ciliary gliding.Meiofauna comprises all organisms between 32 and 1,000 μ m in size that inhabit pore-water-rich sediments in freshwater to deepmarine environments 25 . Modern meiofaunal communities include animals, foraminifera and some ciliates, and contribute significantly to sediment bioturbation and bioirrigation 26,27 . The meiofauna can be divided into permanent members (that is, animals with organisms of a small size adapted and restricted to the meiofaunal, interstitial realm) and temporary meiofauna (for example, the ...

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Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China)

Cited by 64 publications

References 30 publications

Origin of ecdysis: fossil evidence from 535-million-year-old scalidophoran worms

Origin of ecdysis: fossil evidence from 535-million-year-old scalidophoran worms

Anatomy and affinities of a new 535‐million‐year‐old medusozoan from the Kuanchuanpu Formation, South China

Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil

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