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, 104 (15), 6289-92

Raman Spectra of a Lower Cambrian Ctenophore Embryo From Southwestern Shaanxi, China

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Raman Spectra of a Lower Cambrian Ctenophore Embryo From Southwestern Shaanxi, China

Jun-Yuan Chen et al. Proc Natl Acad Sci U S A.

Abstract

The Early Cambrian (approximately 540 million years old) Meishucun fossil assemblage of Ningqiang County (Shaanxi Province), China, contains the oldest complex skeletonized organisms known in the geological record. We here report the finding in this assemblage of an exquisitely preserved late-stage embryo of a ctenophore ("comb jelly"), its fine structure documented by confocal laser scanning microscopy and shown by Raman spectroscopy to be composed of carbonaceous kerogen permineralized in apatite. In its spheroidal morphology, the presence of eight comb rows and the absence of tentacles, this embryo resembles an adult ctenophore (Maotianoascus octonarius) known from the immediately younger Chengjiang fauna of Yunnan, China. The oldest ctenophore and the only embryonic comb jelly known from the fossil record, this exceptionally well preserved specimen provides important clues about the early evolution of the phylum Ctenophora and of metazoans in general.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Optical and Raman images of a thin section-embedded ctenophore embryo from the Lower Cambrian Kuanchuanpu Formation of Ningqiang, Shaanxi Province, China. [Scale bars, 25 μm (A); 10 μm (B–D)]. The Raman images, obtained by recently documented techniques (11), are maps acquired in spectral windows centered on the major Raman bands of the materials analyzed in which varying intensities correspond to the relative concentrations of the molecular structures detected. The blue images (A2, B2, C2, and D2), acquired in a spectral window centered at ≈1,604 cm−1, show the spatial distribution of carbonaceous kerogen; green images (B3, C3, and D3), centered at ≈1,087 cm−1, show the distribution of calcite; and red images (B4, C4, and D4), centered at ≈965 cm−1, show the distribution of apatite. Optical image (A1) and Raman image (A2) of the complete embryo are shown in its kerogenous composition. AC, aboral canal; AO, apical (aboral) organ; EM, egg membrane; MC, meridional canal. Optical image (B1) and Raman images (B2–B4) of the upper left of the specimen (A1) show that it is composed of kerogen (B2) pervaded by fine-grained apatite (B4), the interstices between the structures thus preserved having been infilled by calcite (B3). Optical image (C1) and Raman images (C2–C4) of the middle-right of the specimen (A1) show that the comb plates (ctenes, denoted by CT) are composed of kerogen (C2) augmented by apatite (C4), spaces between them having been infilled by calcite (C3). Optical image (D1) and Raman images (D2–D4) are of the aboral pole of the embryo. AC, aboral canal.
Fig. 2.
Fig. 2.
Overlapping Raman spectra showing the major bands of the apatite, calcite, and kerogen that comprise the embryo described here (baseline subtracted).
Fig. 3.
Fig. 3.
CLSM images of the thin section-embedded embryo, obtained by recently documented techniques (12). [Scale bars, 25 μm (A and D); 10 μm (B, C, and E)]. Because such CLSM images record the laser-excited fluorescence emitted by the kerogen that comprises such fossils, they provide a proxy for direct chemical analyses that show the carbonaceous composition of a specimen analyzed. (A) CLSM image of the complete embryo (see Fig. 1A). The aboral region (B) and middle-right region (C) (see Fig. 1C) of the specimen show the fine-scale morphological information provided by CLSM images. (D) Rotated CLSM image showing comb rows, numbered 1–8, that overlie meridional canals. (E) Higher-magnification image of the aboral region showing the numbered comb rows. AO, apical (aboral) organ; EM, egg membrane; CT, ctenes; AC, aboral canal; MC, meridional canal.

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