Saturday, 5 February 2011
Introducing the Chengjiang Biota
Way back in the Cambrian times (around 542-488 million years ago), recognisable animals appear in the fossil record. Not just one or two, but billions of them, representing most of the major groups (phyla) alive today. The record of trails and burrows also dramatically increases at the same time, which means it isn't entirely a question merely of the fossils being preserved for the first time (although there is probably an element of that too). We call this the Cambrian Explosion.
The reason we know so much is that just at this critical time is that we're lucky enough to have a whole host of exceptionally preserved fossil faunas. The most famous is the Burgess Shale from the Middle Cambrian of Canada, after which the Burgess Shale-type faunas in general are known. It has, however, been largely superceded by an earlier (Early Cambrian) and equally spectacular fauna from China: the Chengjiang Biota.
These faunas contain a wide range of creatures, and both fossils and reconstructions are on display in the Nanjing Museum of Palaeontology, at the Institute. The big beastie in this picture is an anomalocarid - probably the top predators of the time, and distantly related to modern crustaceans, spiders and their jointy-limbed families. At top right is an eldoniid - what that is, we have too many ideas and no consensus. The same goes for the vetulicolian in front of the anomalocaridid's grasping appandages, and it's a group that has been the source of many arguments in recent years. Arthropod, or fish-like creature? Despite exquisite detail, it's so different to anything alive now that it's hard to say.
There are various sponges, arthropods and so forth in the background - both the Burgess and Chengjiang have well over a hundred species known so far, and more still turning up. And in China, there are now a host of new deposits that look to rival Chengjiang - Guanshan, Kaili, Hetang, Zunyi... this is why palaeontologists worldwide are now looking to China with envy!*
* Well, the feathered dinosaurs help a bit. As do the Precambrian embryos, the dinosaur nests, the...