Cambrian sites
From Palaeos.org
| Cambrian period 542-488 | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Terreneuvian 542-521 | Series 2 521-510 | Series 3 510-499 | Furongian 499-488 | ||||||
| Fortunian 542-528 | Stage 2 528-521 | Stage 3 521-515 | Stage 4 515-510 | Stage 5 510-506 | Drumian 506-503 | Guzhangian 503-499 | Paibian 499-496 | Stage 9 496-492 | Stage 10 492-488 |
1) Chengjiang
The faunal list from Chengjiang is a virtually complete census of the major metazoan taxa of the time, and includes our personal favorite of all early chordates, Haikouella. There seems to be little selectivity. There are now Chengjiang fossil images all over the web. However, many of the Chengjiang organisms remain undescribed, simply for lack of competent describers, and new specimens are being discovered at an extraordinary rate. Many species have undergone revisions, and contention among scientists about interpretations is commonplace.
2) The Burgess Shale
The Burgess Shale is slightly younger than Chengjiang. The Shale is located near the town of Field, in southeastern British Columbia, high in the Canadian Rockies. The closest major town is Banff, about 90 km to the east. The site was discovered by Charles Walcott of the Smithsonian Institution in 1909, and the Walcott Quarry is named after him. The deposits are deepwater, benthic sediments, but the fauna probably represent a reef community swept off the reef and buried in an anoxic bottom by a mudslide. The Burgess is actually far less spectacular than Chengjiang, but it attained great fame (ironically, just at the time that Chengjiang was starting to produce large quantities of fossils) due in part to Stephen Jay Gould's book, Wonderful Life.
The Burgess Shale's influence on paleontology has been, in part, due to the fact that Gould chose this book to set out some of his most interesting and controversial ideas about evolution, and in a manner readable by almost everyone. Gould argued that the end results of evolution were essentially random because the process was chaotic [2]. Thus even the tiniest change in Proterozoic conditions might have resulted in an entirely different modern fauna. His proof was the diversity of phyla in the Shale, hinting at an enormous initial diversity in the Cambrian Explosion which was quickly pruned away, largely by happenstance. As it has turned out, Gould was certainly wrong about the Burgess Shale. Chengjiang - and closer examination of the Burgess fauna - have shown that Walcott was more correct than Gould. The great majority of Burgess animals can now be assigned with confidence to well-known phyla. However, his ideas about evolution may well be correct, if the pruning process actually occurred in the lower Early Cambrian or even before metazoans became morphologically recognizable.
notes:
[1] We use the Russian-Kazakhian stages until the ICS gets around to finally giving these Early Cambrian ages some names. As of this date (100406), the ICS age corresponding to the Botomian is still unnamed.
[2] We use chaotic in its mathematical sense, meaning that the end state of a closed system is extremely sensitive to initial conditions. The classical example is from meteorology, in which the occurrence of a hurricane is supposedly determined by the wing beat of a butterfly six months earlier and ten thousand miles away.
Palaeos com - Paleozoic
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