The Cambrian period succeeded the breakup of the global supercontinent, Pannotia. Its remaining contiguous landmass, Gondwanaland, stretched from the southern polar regions to the Tropic of Cancer. To the west, a ribbon of continents straddled the southern tropics: Avalonia, Baltica, Siberia, and Laurentia. The overall mean global temperatures in the Cambrian were several degrees higher than today, but Gondwanaland began the period covering the South Pole and experienced substantial glaciation. Over the course of the Cambrian, temperatures, and sea levels rose appreciably, and ice caps disappeared. Arthropods were the dominant life form in the oceans, with trilobites being the most celebrated example. Fossilized tracks from this time, indicate some had made it on to land. The Cambrian Explosion describes a spike in biodiversity early in the period: it would be followed by a succession of mass extinctions, and the period ended in a relative dearth of life forms.
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