What important event in animal evolution marks the beginning of the cambrian period?
the ability to swim

the ability to fly

the appearance of hard parts

the appearance of fossils

The appearance of fossils would the the answer.

Although there has been some scientific debate about what fossil strata should mark the beginning of this period, the "International Geological Congress" determined that the Cambrian period was approximately 543 million years ago of which the first appearance in the fossil record of worms that made horizontal burrows was discovered.

the aswer is letter c

answer; i believe the correct answer is (replication is not conservative);