Cambrian - Fauna

Fauna

Most animal life during the Cambrian was aquatic. The period marked a steep change in the diversity and composition of Earth's biosphere. The incumbent Ediacaran biota suffered a mass extinction at the base of the period, which corresponds to an increase in the abundance and complexity of burrowing behaviour. This behaviour had a profound and irreversible effect on the substrate which transformed the seabed ecosystems. Before the Cambrian, the sea floor was covered by microbial mats. By the end of the period, burrowing animals had destroyed the mats through bioturbation, and gradually turned the seabeds into what they are today. As a consequence, many of those organisms who were dependent on the mats went extinct, while the other species adapted to the changed environment who now offered new ecological niches. Around the same time there was a seemingly rapid appearance of representatives of all the mineralized phyla. However, many of these phyla were represented only by stem-group forms; and since mineralized phyla generally have a benthic origin, they may not be a good proxy for (more abundant) non-mineralized phyla.

Some Cambrian organisms ventured onto land, producing the trace fossils Protichnites and Climactichnites. Fossil evidence suggests that euthycarcinoids, an extinct group of arthropods, produced at least some of the Protichnites. Fossils of the maker of Climactichnites have not been found; however, fossil trackways and resting traces suggest a large, slug-like mollusk.

In contrast to later periods, the Cambrian fauna was somewhat restricted; free-floating organisms were rare, with the majority living on or close to the sea floor; and mineralizing animals were rarer than in future periods, in part due to the unfavourable ocean chemistry. (Most Cambrian carbonates were formed by microbial or non-biological processes.)

Many modes of preservation are unique to the Cambrian, resulting in an abundance of lagerstätte.