Cambrian

Temperature: 21 °C
Atmospheric oxygen: 12.5%

The Cambrian period was the first geological period of the Paleozoic era, it marked a profound change in life on Earth. Prior to the Cambrian, the majority of living organisms were small and simple. However, in the Cambrian rapid diversification occurred, in an event is known as the Cambrian Explosion. The great glaciers of the Proterozoic era were long melted – the sea level was high, which led to large areas of the continents being flooded by warm, shallow seas ideal for sea life.
The Earth was generally cool during the Early Cambrian, probably due to the ancient continent of Gondwana covering the South Pole and cutting off polar ocean currents. However, average temperatures were still 7 degrees higher than today. There were likely polar ice caps and a series of glaciations, but it became warmer towards the end of the period; the glaciers retreated and eventually disappeared, and sea levels rose dramatically. This trend would continue into the Ordovician period.

Animals

•Hallucigenia

Hallucigenia is a genus of Cambrian xenusiids known from articulated fossils in Burgess Shale-type deposits in Canada and China, and from isolated spines around the world.

•Conodonta


Conodonts are extinct agnathan chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils found in isolation and now called conodont elements. Knowledge about soft tissues remains limited.

•Myllokunmingia

Myllokunmingia is a genus of basal chordate from the Lower Cambrian Maotianshan shales of China, thought to be a vertebrate, although this is not conclusively proven. It is 28 mm long and 6 mm high. It is among the oldest possible craniates, found in the lower Cambrian Chengjiang.

•Opabinia

Opabinia regalis is an extinct, stem group arthropod found in the Middle Cambrian Burgess Shale Lagerstätte of British Columbia, Canada. Fewer than twenty good specimens have been described; 3 specimens of Opabinia are known from the Greater Phyllopod bed, where they constitute less than 0.1% of the community.

•Marrellag


Marrella splendens is an extinct arthropod known from the middle Cambrian Burgess Shale of British Columbia. It is the most common animal represented in the Burgess Shale.