I know this is two paleontological posts in a row, but I had intended to blog about this before the stunning KT discovery. Chinese paleontologists announce in the journal Science a new early Cambrian fossil bed in South China – the The Qingjiang biota.

This is now just the third major Cambrian find – the first being the famous Burgess shale, and the second the Chengjiang, also in China. This find is amazing for several reasons.

First, the Cambrian Explosion is an incredibly important period in the evolution of life. The Cambrian period lasted from 541 to 485 million years ago. This was the first appearance of the multicellular life that clearly lead to all subsequent plants and animals, including modern species. There was a previous period called the Ediacara fauna, but it is still unclear if this lead to the Cambrian life or was a side branch or even an independent origin of multicellular life that didn’t make it. Recent evidence suggests that some Ediacara life were animals, and therefore ancestors to some Cambrian life and not a total dead end. But this is still not fully resolved.

Either way, the massive diversification of multicellular life in the Cambrian period lead to all the modern phyla, and many additional phyla that did not survive the Cambrian. Our first real evidence of this diversification was from a famous fossil find in Canada, the Burgess Shale. Most of what we know about the Cambrian still comes from these fossils.

Paleontologists talk about fossil windows, because a particular location will be a virtual window into one place and time in the past. A fossil bed will be from one time period, and will have formed because the conditions were right at the time. Burgess creatures were mostly soft-bodied, and so they require even more special conditions to be preserved well-enough that modern paleontologist can reconstruct them.

This is why shale is a good medium for such fossils. Shale is formed by layers of sediment, which is excellent for preserving dead plants and animals so that they can fossilize. A fine sediment can also allow for the preservation of fine structures. So the Burgess Shale is an amazing window into the Cambrian period.

The Chengjiang is another shale fossil bed dating from 525 million years ago, giving us a second window into this period. Now we have a third, the Qingjian biota, dating from 514 million years ago. While these three sites are all Cambrian, they are separated by millions of years. Further, the two Chinese sites are on the opposite side of the world from the Burgess site, and there is no reason to expect they will contain the same assemblage of species any more than that would be true today.

So far scientists have collected 20,000 samples from Qingjian, and examined 4,000 of them. They have identified 101 genera, and 50 of them are previously unknown – half of the fossil genera they have discovered are new.

This highlights the fact that, despite the massive number of fossils and fossil species we have collected, this still represents a tiny random sampling of all the life that has existed. A new large fossil find is still likely to contain many new kinds of creatures.

As an aside, paleontologist tend to speak of genera, the plural of genus, when discussing new life forms. Genus is one level up from species in taxonomy, and essentially represents what we think of as an animal or plant type. Most of the animals, extant or extinct, that you think of are really a genus with multiple species. A zebra, for example, is a genus with three species. A giraffe is also a genus. The same is true for dinosaurs – pretty much all the dinosaur types you know are really genera, not species.

Even though we now have three major Cambrian biota, with some overlap but also many differences, this still may represent a small sampling of all the life that existed in that period. However, we may have identified all the phyla that existed at that time. That is going to the other end of the taxonomic scale – phyla are the major divisions withing kindgoms, like plants or animals. Identifying a new phyla would be a huge discovery. There may be more out there from the Cambrian to be discovered, but it’s also possible that our random sampling has found them all already.

An of course there is everything in between – classes, orders, families, etc. The tree of life is huge with many branches. We are slowly filling in the picture, and we really can’t know how much more remains to be discovered until we find it. We have some idea when there are missing pieces, but we can’t know how much detail is filling in that missing space in our picture. It always turns out to be more than we thought.

Like the KT find I discussed yesterday, the Qingjian biota will keep paleontologists busy for many decades. This is a treasure trove of well-preserved soft-bodied fossils from an incredibly interesting an important time in the history of life, and we have just scratched the surface.