Embryo Fossils From The Early Cambrian Kuanchuanpu Fauna And Their Development Biology

The Cambrian explosion is marked by the apparent sudden appearance of diverse metazoan skeletal fossils and an increase in the complexity of both body and trace fossils. This unique Big Bang of life has been recognized as giving birth to the entire morphological Tree Of Animals (or metazoans), in short the TOA. Among them, fossil eggs and embryos from the Lower Cambrian Kuanchuanpu Member of the Dengying Formation at Ningqiang in southern China provide a unique window to investigate the evolution of specific development processes and by examining the morphological transition process from embryo to adult during the Neoproterozoic to the Cambrian.After maceration of the phosphatic limestone rock samples, thousands of globular fossils were handpicked from the rock residue. Then, several specimens examined under scanning electron microscope (SEM) were mounted on slides using double-sided carbon tape. These fossils include nearly completely developmental stages (cleavage, gastrula, larva and organic stage) of animal embryos. Based on these extraordinarily preserved embryos, we discussed several theories in evolutional development and embryology of early animals as follows.1) Evolution of the embryo cleavage pattern; 2) Origin and evolution of the embryo gastrulation; 3) New data of radial symmetrical metazoans from the Lower Cambrian Kuanchuanpu Fauna; 4) Discussion of several evolutional development theories (i.e., origin of Penta-radial symmetry, Direct-development & Indirect-development, origin of Diploblastica, origin of Homoblastica et al.).