New Early Cambrian bilaterian embryos and larvae from China

Steiner, Michael; Zhu, Maoyan; Li, Guoxiang; Qian, Yi; Erdtmann, Bernd-Dietrich

doi:10.1130/g20567.1

Cited by 101 publications

(65 citation statements)

References 14 publications

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“…On hatching, the aperture expanded, transforming the spheroid into a conical structure, the 'Punctatus' stage (figure 1h-k), which increased in height through development, with growth at the aperture that appears to have been capable of opening and closure. The evidence of association between the later developmental stages rests with the presence of a characteristic stellate and ribbed integument as well as pentaradial symmetry in both the putative embryonic and the post-embryonic stages; the attribution of associated cleavage stages to Olivooides is currently based solely on co-association [5,12]. SRXTM of numerous specimens has shown that, cleavage embryos aside, internal preservation of Olivooides embryos is exceedingly rare [13].…”

Section: Resultsmentioning

confidence: 99%

Embryos, polyps and medusae of the Early Cambrian scyphozoan Olivooides

et al. 2013

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The Early Cambrian organism Olivooides is known from both embryonic and post-embryonic stages and, consequently, it has the potential to yield vital insights into developmental evolution at the time that animal body plans were established. However, this potential can only be realized if the phylogenetic relationships of Olivooides can be constrained. The affinities of Olivooides have proved controversial because of the lack of knowledge of the internal anatomy and the limited range of developmental stages known. Here, we describe rare embryonic specimens in which internal anatomical features are preserved. We also present a fuller sequence of fossilized developmental stages of Olivooides, including associated specimens that we interpret as budding ephyrae ( juvenile medusae), all of which display a clear pentaradial symmetry. Within the framework of a cnidarian interpretation, the new data serve to pinpoint the phylogenetic position of Olivooides to the scyphozoan stem group. Hypotheses about scalidophoran or echinoderm affinities of Olivooides can be rejected.

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Section: Resultsmentioning

confidence: 99%

Embryos, polyps and medusae of the Early Cambrian scyphozoan Olivooides

et al. 2013

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“…Non-biomineralized ecdysozoans, however, existed before, as evidenced by: (1) fossilized embryos of Markuelia secunda Val'kov from the basal Tommotian Stage in Siberia, having already a sclerotized cuticle and representing the Scalidophora, a sub-group of the Cycloneuralia (Bengtson & Yue, 1997;Dong et al 2004Dong et al , 2005Dong et al , 2010; embryos and possibly related larvae of Pseudooides prima from the lower Meishucunian Stage of South China, considered as possible stem-group arthropods (Steiner et al 2004b) and (2) the arthropod-type trace fossils in pre-trilobitic strata (Crimes, 1987;Weber & Zhu, 2003;Weber, Steiner & Zhu, 2007).…”

Section: Discussionmentioning

confidence: 99%

Chronology of early Cambrian biomineralization

et al. 2011

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-Data on the first appearances of major animal groups with mineralized skeletons on the Siberian Platform and worldwide are revised and summarized herein with references to an improved carbon isotope stratigraphy and radiometric dating in order to reconstruct the Cambrian radiation (popularly known as the 'Cambrian explosion') with a higher precision and provide a basis for the definition of Cambrian Stages 2 to 4. The Lophotrochozoa and, probably, Chaetognatha were first among protostomians to achieve biomineralization during the Terreneuvian Epoch, mainly the Fortunian Age. Fast evolutionary radiation within the Lophotrochozoa was followed by radiation of the sclerotized and biomineralized Ecdysozoa during Stage 3. The first mineralized skeletons of the Deuterostomia, represented by echinoderms, appeared in the middle of Cambrian Stage 3. The fossil record of sponges and cnidarians suggests that they acquired biomineralized skeletons in the late Neoproterozoic, but diversification of both definite sponges and cnidarians was in parallel to that of bilaterians. The distribution of calcium carbonate skeletal mineralogies from the upper Ediacaran to lower Cambrian reflects fluctuations in the global ocean chemistry and shows that the Cambrian radiation occurred mainly during a time of aragonite and high-magnesium calcite seas.

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“…The early fossil embryos so far described are large, ranging from 350 to 1100 mm (Xiao & Knoll 2000) for Late Precambrian embryos to 350-750 mm for Early-Mid-Cambrian embryos (Steiner et al 2004;Donoghue et al 2006). There are biases in the record, notably low taxonomic diversity .…”

Section: Hunting the Larval Revolution In The Fossil Recordmentioning

confidence: 99%

Origins of the other metazoan body plans: the evolution of larval forms

Raff

2008

Phil. Trans. R. Soc. B

137

101

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Bilaterian animal body plan origins are not solely about adult forms. Most animals have larvae with body plans, ontogenies and ecologies distinct from adults. There are two primary hypotheses for larval origins. The first hypothesis suggests that the first animals were small pelagic forms similar to modern larvae, with adult bilaterian body plans evolved subsequently. The second hypothesis suggests that adult bilaterian body plans evolved first and that larval body plans arose by interpolation of features into direct-developing ontogenies. The two hypotheses have different consequences for understanding parsimony in evolution of larvae and of developmental genetic mechanisms. If primitive metazoans were like modern larvae and distinct adult forms evolved independently, there should be little commonality of patterning genes among adult body plans. However, sharing of patterning genes is observed. If larvae arose by co-option of adult bilaterian-expressed genes into independently evolved larval forms, larvae may show morphological convergence, but with distinct patterning genes, and this is observed. Thus, comparative studies of gene expression support independent origins of larval features. Precambrian and Cambrian embryonic fossils are also consistent with direct development of the adult as being primitive, with planktonic larvae arising during the Cambrian. Larvae have continued to co-opt genes and evolve new features, allowing study of developmental evolution.

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New Early Cambrian bilaterian embryos and larvae from China

Cited by 101 publications

References 14 publications

Embryos, polyps and medusae of the Early Cambrian scyphozoan Olivooides

Embryos, polyps and medusae of the Early Cambrian scyphozoan Olivooides

Chronology of early Cambrian biomineralization

Origins of the other metazoan body plans: the evolution of larval forms

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