Deciphering the fossil record of early bilaterian embryonic development in light of experimental taphonomy

摘要: Experimental analyses of decay in a tunicate deuterostome and three lophotrochozoans indicate that the controls on preservation embryos, identified previously based echinoids, are more generally applicable. Four stages regardless environment death decay. Embryos rapidly oxic anoxic conditions, although gross morphology embryos is maintained for longer under conditions. Under reducing longest period time, compatible with timescale required bacterially mediated mineralization soft tissues. All four were encountered all environmental matching spectrum preservational qualities fossil embryo assemblages. The potential deuterostomes at odds lack such record. Rather, record as sparse it is, dominated by forms interpreted ecdysozoans, cnidarians, stem-metazoans. dearth lophotrochozoan may be explained fact least, tend to deposit their eggs sediment rather than through broadcast spawning. However, remain very rare main controlling factor fossilization unique conspiracy conditions couple sites. preponderance fossilized direct developers should not used evidence against existence indirect development this time animal evolutionary history.