Paleozoic Era		Cambrian Epoch 2
Cambrian Period		Cambrian age IV ("Botomian" Age)

The Botomian Age

The Botomian Age of Cambrian Epoch 2: ~517 to ~510 million years ago

Trilobites and Archaeocyaths diversify

The ICS does not yet recognize any formal divisions of the Early Cambrian.  See sarcastic comments at Atdabanian Age.  We apply the Russian-Kazakhian regional nomenclature. It appears that the Botomian and Toyonian Ages will be combined on that happy day when ICS finally gets around to telling us what to call anything in the first 29 My of the Cambrian.  

Relative to later ecosystems, the Cambrian ecology was extremely delicate. This may be due to the fact that diveristy was very low, compared to modern ecosystems, and so environmental disruptions could easily wreak havoc (we are witnessing the groundworl of what may well be a similar disaster today - human stupidity and short-sightedness means that large areas of wilderness and biodiversity are being destroyed, to make way for extensive fields of ecologically vulnerable monocultures.)

The Botomian witnessed a mass extinction that may have been even more severe than the end Permian extinction, in terms of absolute percentages of species lost. Some 83% of genera of hard-shelled or -bodied animals did not survive into the Middle Cambrian. However, relative to the rest of the Cambriabn this wasn't so bad. The Cambrian background extinctions between stages was about 40%, compared with about 5% in the Permian. So the Permain extinction was ten times the normal rate whereas the Botomian extinction rate was only twice the background rate.