… The 500 million subsequent years have produced no new phyla …
Continuing through Wonderful Life: The Burgess Shale and the Nature of History by Stephen Jay Gould (1989):
… Why did life remain at stage 1 [prokaryotic cells and nothing else] for two-thirds of its history if complexity offers such benefits? Why did the origin of multicellular life proceed as a short pulse through three radically different faunas, rather than as a slow and continuous rise of complexity?
[ … ]
… most animals have no hard parts. In 1978, Schopf analyzed the potential for fossilization of an average modern marine fauna of the intertidal zone. He concluded that only 40 percent of genera could appear in the fossil record. Moreover, potential representation is strongly biased by habitat. About two-thirds of the sessile (immobile) creatures living on the sea floor might be preserved, as contrasted with only a quarter of the burrowing detritus feeders and mobile carnivores.
[line break added] Second, while the hard parts of some creatures — vertebrates and arthropods, for example — are rich in information and permit a good reconstruction of the basic function and anatomy of the entire animal, the simple roofs and coverings of other creatures tell us nearly nothing about their underlying organization. A worm tube or a snail shell implies very little about the organism inside, and in the absence of soft parts, biologists often confuse one for the other.
… Paleontologists have therefore sought and treasured soft-bodies faunas since the dawn of the profession. No pearl has greater price in the fossil record. Acknowledging the pioneering work of our German colleagues, we designate these faunas of extraordinary completeness and richness as Lagerstätten (literally “lode places,” or “mother loads” in freer translation). Lagerstätten are rare, but their contribution to our knowledge of life’s history is disproportionate to their frequency by orders of magnitude.
… Clearly, the Burgess pattern of stunning disparity in anatomical design is not characteristic of well-preserved fossil faunas in general. Rather, good preservation has permitted us to identify a particular and immensely puzzling aspect of the Cambrian explosion and its immediate aftermath. In a geological moment near the beginning of the Cambrian, nearly all modern phyla made their first appearance, along with an even greater array of anatomical experiments that did not survive very long thereafter.
[line break added] The 500 million subsequent years have produced no new phyla, only twists and turns upon established designs — even if some variations, like human consciousness, manage to impact the world in curious ways. What established the Burgess motor? What turned it off so quickly? What, if anything, favored the small set of surviving designs over other possibilities that flourished in the Burgess Shale? What is this pattern of decimation and stabilization trying to tell us about history and evolution?