Synchrotron X-ray tomographic microscopy of fossil embryos

Abstract

Fossilized embryos from the late Neoproterozoic and earliest Phanerozoic have caused much excitement because they preserve the earliest stages of embryology of animals that represent the initial diversification of metazoans. However, the potential of this material has not been fully realized because of reliance on traditional, non-destructive methods that allow analysis of exposed surfaces only, and destructive methods that preserve only a single two-dimensional view of the interior of the specimen. Here, we have applied synchrotron-radiation X-ray tomographic microscopy (SRXTM), obtaining complete three-dimensional recordings at submicrometre resolution. The embryos are preserved by early diagenetic impregnation and encrustation with calcium phosphate, and differences in X-ray attenuation provide information about the distribution of these two diagenetic phases. Three-dimensional visualization of blastomere arrangement and diagenetic cement in cleavage embryos resolves outstanding questions about their nature, including the identity of the columnar blastomeres. The anterior and posterior anatomy of embryos of the bilaterian worm-like Markuelia confirms its position as a scalidophoran, providing new insights into body-plan assembly among constituent phyla. The structure of the developing germ band in another bilaterian, Pseudooides, indicates a unique mode of germ-band development. SRXTM provides a method of non-invasive analysis that rivals the resolution achieved even by destructive methods, probing the very limits of fossilization and providing insight into embryology during the emergence of metazoan phyla.

Embryo fossilization is a biological process mediated by microbial biofilms

“…The frequency of these mineralization modes remains to be determined for embryos. However, all fossil embryos show evidence of decay and, in the vast majority of cases, decay has been so considerable that only gross features such as the fertilization envelope or other outer coverings remain (12,13,29). Thus, embryo fossils are, to a greater or lesser degree, microbial pseudomorphs of the original cells and this fabric can be seen replicated in mineral.…”

Floral Structure of Extant Quintinia (Paracryphiales, Campanulids) Compared with the Late Cretaceous Silvianthemum and Bertilanthus

“…The holotype for Silvianthemum suecicum (S100376), three other specimens of Silvianthemum (S171503, S171556, S171578), as well as three specimens of Q. quatrefagesii (flower bud, anthetic flower, postanthetic flower) were studied using SRXTM at the TOMCAT beamline of the Swiss Light Source at the Paul Scherrer Institute, Switzerland, using objective #10 at 10 keV, following the technique outlined by Donoghue et al (2006). Vertical stacking was applied for several specimens and lateral stacking for the anthetic flower of Q. quatrefagesii.…”

Cutting the first ‘teeth’: a new approach to functional analysis of conodont elements

“…Following the apparatus reconstruction of Sansom et al [16], six element morphotypes of Panderodus acostatus, from a single sample of the Upper Visby beds, basal Wenlock, Gotland, Sweden, were characterized volumetrically using synchrotron radiation X-ray tomographic microscopy (SRXTM) [18]. From this tomographic dataset, three-dimensional renderings of the external morphology of each element were made, and virtual sections derived.…”