T130 Fossil Preservation, Biological Evolution, and Environmental Change at the Dawn of Animal Radiation: An Examination of Geobiological Events across the Ediacaran–Cambrian Transition II

Monday, 5 November 2012
1:30 PM - 5:30 PM
217D

SYNCHROTRON X-RAY MICRO-CT ANALYSES OF THE EARLY CAMBRIAN MICROFOSSILS

Paper number: T130-2
Program: Technical Sessions
Time: 1:45 PM – 2:00 PM

Authors

Abstract

Cambrian Explosion, the most drastic event in history of life on Earth. Chemopaleontological studies around the event are very important to reveal early evolution of Metazoa. Recent X-ray micro-CT analyses of microfossils yielded new methods to observe the internal structures (e.g. Donoghue et al., 2006). Compared with microscopic and SEM observations of cutting planes of the microfossils, the technique has two advantages of “nondestructive” analyses on “any” cross-sections of internal structures. This work presents observations of three-dimensional structures of about 60 specimens of the Early Cambrian microfossils, interpreted as embryo, larvae, Anthozoa, Hydrozoa, Echinodermata with a Synchrotron X-ray micro-CT at SPring-8, Japan (BL47XU). The fossils occur at Shizhonggou area, Shanxi Province, China, together with Anabarites and Protohertzina (Yao et al., 2011).

Yao et al., (2011) proposed various Olivooides fossils as each stage of Gastrulation based on the external morphology (Epiboly). Our direct observation of the interiors reveals a blastopore, supporting the interpretation. In addition, their other cross-sections display ten-fold radial structures. Cheng and Dong (2008) showed five-fold structures on top of Punctatus. Our observations show the five or ten-fold structures are present even in the Gastrula. Micro-CT observations of internal structures of sea anemone-like microfossils display digestive systems of mouth, gastrovascular cavity and partitions. In addition, the Micro-CT analyses show that microfossils, interpreted as polyps of Cnidaria, have pentaradial symmetry, apparently inconsistent between the external and internal morphology. High-resolution observations of internal structures of microfossils with the Synchrotron X-ray micro-CT possibly help in developing insight into early biological evolution from diploblastic to triploblastic organisms as well as into the classification.