The details of how animal life began are a bit murky. Most of the groups familiar today are present in the Cambrian, a period when they rapidly diversified, with familiar features evolving alongside bizarre creatures with no obvious modern equivalents. There are hints that some forms of present animal life predated the Cambrian. But most of the organisms we've found in Ediacaran deposits have no obvious relationship to anything we're familiar with. The complete absence of these creatures in later strata suggests they might have vanished in a mass-extinction event that cleared the way for the explosion of Cambrian species. But a new series of fossils found at a site in China includes examples of groups that flourished in the Cambrian living side by side with a few Ediacaran species. The deposits suggest that there might have been a gradual shift into the Cambrian.…