Sponge grade body fossil with cellular resolution dating 60 Myr before the Cambrian - PubMed (original) (raw)

Sponge grade body fossil with cellular resolution dating 60 Myr before the Cambrian

Zongjun Yin et al. Proc Natl Acad Sci U S A. 2015.

Abstract

An extraordinarily well preserved, 600-million-year (Myr)-old, three-dimensionally phosphatized fossil displaying multiple independent characters of modern adult sponges has been analyzed by SEM and synchrotron X-ray tomography. The fossilized animal (Eocyathispongia qiania gen. et sp. nov.) is slightly more than 1.2 mm wide and 1.1 mm tall, is composed of hundreds of thousands of cells, and has a gross structure consisting of three adjacent hollow tubes sharing a common base. The main tube is crowned with a large open funnel, and the others end in osculum-like openings to the exterior. The external surface is densely covered with flat tile-like cells closely resembling sponge pinacocytes, and this layer is punctuated with smaller pores. A dense patch of external structures that display the form of a lawn of sponge papillae has also survived. Within the main funnel, an area where features of the inner surface are preserved displays a regular pattern of uniform pits. Many of them are surrounded individually by distinct collars, mounted in a supporting reticulum. The possibility cannot be excluded that these pits are the remains of a field of choanocytes. The character set evinced by this specimen, ranging from general anatomy to cell type, uniquely indicates that this specimen is a fossil of probable poriferan affinity. So far, we have only this single specimen, and although its organized and complex cellular structure precludes any reasonable interpretation that its origin is abiogenic, confirmation that it is indeed a fossilized sponge will clearly require discovery of additional specimens.

Keywords: Doushantuo Formation; Precambrian; metazoan phylogeny; sponge fossil; synchrotron X-ray tomography.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Fig. 1.

Overall anatomy of the specimen. (A) Scanning electron micrograph showing the main tubular chamber with a large opening and additional chambers viewed from the exterior. (B) Outflow orifices. (B, 1) Scanning electron micrograph of a top-down view of A with three openings marked by colored frames; opening 1 is the large opening in the upper center of A. (B, 2_–_4) Scanning electron micrograph close-up views of putative outflow openings located by frames in B, 1. Note the dense covering of flattened surface cells in B, 2_–_4. The arrow in B, 3 shows the location of images in Fig. 2 B, 1 and 2; the arrow in B, 4 shows the orifice highlighted in B, 2. (C) Three-dimensional digital PPC-SR-μCT reconstructions with a surface rendering (upper left) showing the location of three openings and the remaining digital sections (left to right, upper to lower) showing increasing depth indicating three separate chambers [chamber 1 (C1), chamber 2 (C2), and chamber 3 (C3)] emerging from a common base that appears white in the image.

Fig. 2.

Fig. 2.

Flattened surface cells and base or holdfast. (A, 1 and 2) Scanning electron micrograph close-up views showing flattened surface cells; the yellow circles indicate the gaps and pores between cells. (B) External edge of the funnel. (B, 1 and 2) Scanning electron micrograph close-up views of the rim of the funnel indicated by the arrow in Fig. 1 B, 3, showing that body wall is three to six cells thick. (C) Base or holdfast of specimen. (C, 1) Digital PPC-SR-μCT section showing regionally distinctive areas (indicated by pink frames) within the basal portion of the specimen. (C, 2) Digital PPC-SR-μCT section close-up of the area indicated in C, 1 showing the boundary between the outer layer of the cells and the inner structural material. (C, 3) Digital PPC-SR-μCT section close-up of the area indicated in C, 1 showing the differentially structured domain within the parenchymal material, which appears in the computational cross-section as a disk containing low-density dark spots that may be cavities or cells.

Fig. 3.

Fig. 3.

Modern sponge anatomy. (A) Schematic cross-section of simple asconoid sponge morphology with a central cavity and base. Pores (ostia) in body wall carry water inflow, and the large orifice (osculum) is used for outflow (arrows indicate direction of water flow). (B) Schematic cross-section showing three layers of the body wall, including external pinacocyte cells, internal choanocyte cells, and mesohyl separating them; incurrent pores in the body wall (ostia); and an excurrent opening (osculum) to the body chamber (spongocoel), as well as additional cell types (porocyte and amebocyte). (C) Surface of the demosponge Polymastia penicillus showing hollow papillae up to 1 cm long. Image courtesy of Bernard Picton (Department of Natural Sciences, National Museums Northern Ireland, Cultra, Holywood, United Kingdom). (D) Schematic of a small portion of the flagellated chamber wall of a hexactinellid sponge, based on light microscopy of several species and EM of Rhabdocalyptus dawsoni. Modified from data from ref. . From the surface, the inner reticulum of the trabecular syncytium provides a matrix-like structure surrounding the collars, from within which extend choanocyte flagellae. b.r, basal reticulum of trabecular syncytium; c, collar; c.b., collar body; i.r., inner or secondary reticulum of trabecular syncytium; n., nucleus of trabecular syncytium; p., prosopyle.

Fig. 4.

Fig. 4.

Specialized surface structures. (A) Scanning electron micrograph of the exterior with the framed area showing the location of a patch of short, hollow tubes. (B and C) Scanning electron micrograph close-up views showing details of these surface-specialized tube structures.

Fig. 5.

Fig. 5.

Interior surface structures. (A) Digital PPC-SR-μCT section slicing vertically through the main funnel opening shown in Fig. 1_A_. (B) Magnification of the marked area in A, showing interior surface pit structures. (C) Scanning electron micrograph of the big opening, showing the same interior surface pit structures as in B. (D and E) Close-up views of these interior surface structures of C, showing details of pits and surrounding features. A reticular structure surrounds the regularly spaced pits, which often display clearly preserved circular collars (red arrowheads).

References

    1. Erwin D, Valentine J. The Cambrian Explosion. Roberts and Company Publishers; Greenwood Village, CO: 2012.
    1. Ryan JF, et al. NISC Comparative Sequencing Program The genome of the ctenophore Mnemiopsis leidyi and its implications for cell type evolution. Science. 2013;342(6164):1242592. -PMC -PubMed
    1. Nosenko T, et al. Deep metazoan phylogeny: When different genes tell different stories. Mol Phylogenet Evol. 2013;67(1):223–233. -PubMed
    1. Riesgo A, Farrar N, Windsor PJ, Giribet G, Leys SP. The analysis of eight transcriptomes from all poriferan classes reveals surprising genetic complexity in sponges. Mol Biol Evol. 2014;31(5):1102–1120. -PubMed
    1. Srivastava M, et al. The Amphimedon queenslandica genome and the evolution of animal complexity. Nature. 2010;466(7307):720–726. -PMC -PubMed

Publication types

MeSH terms

LinkOut - more resources