title: 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.
authors.affiliation: Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK. phil.donoghue@bristol.ac.uk
authors.forename: Philip C J
authors.initials: PC
authors.lastname: Donoghue
authors.forename: Stefan
authors.initials: S
authors.lastname: Bengtson
authors.forename: Xi-ping
authors.initials: XP
authors.lastname: Dong
authors.forename: Neil J
authors.initials: NJ
authors.lastname: Gostling
authors.forename: Therese
authors.initials: T
authors.lastname: Huldtgren
authors.forename: John A
authors.initials: JA
authors.lastname: Cunningham
authors.forename: Chongyu
authors.initials: C
authors.lastname: Yin
authors.forename: Zhao
authors.initials: Z
authors.lastname: Yue
authors.forename: Fan
authors.initials: F
authors.lastname: Peng
authors.forename: Marco
authors.initials: M
authors.lastname: Stampanoni
mesh_terms: D000818:Animals; D001757:Blastomeres / Q000166:cytology / Q000648:ultrastructure; D002681:China; D003063:Cnidaria / Q000033:anatomy & histology / Q000166:cytology / Q000196:embryology* / Q000648:ultrastructure; D004625:Embryo, Nonmammalian / Q000033:anatomy & histology / Q000166:cytology / Q000648:ultrastructure; D005580:Fossils; D049690:History, Ancient; D007814:Larva / Q000648:ultrastructure; D008853:Microscopy / Q000379:methods*; D012800:Siberia; D017356:Synchrotrons; D013997:Time Factors; D014056:Tomography, X-Ray / Q000379:methods*; D014965:X-Rays