EXPLOSIVE SALTATIONS. “One group of coral-like sea organisms in particular, called bryozoan, shows this kind of pattern. The well-preserved fossil record of bryozoans shows that one species first appeared about 140 million years ago and remained unchanged for its first 40 million years. Then there was an explosion of diversification, followed by another period of stability for vast amounts of time.”
http://www.pbs.org/wgbh/evolution/library/03/5/l_035_01.html