Australia: The Land Where Time Began

A biography of the Australian continent 

Cambrian Explosion - General Patterns

Discussion of the evolution of metazoan architectures during the Cambrian Explosion led to the emergence of several general patterns. By the end of Stage 3 members of most phylum-level clades must have been present, at least as stem groups. Crown groups at class level had arisen, such as Lingulida among the Brachiopoda, Bivalvia among the Mollusca, and among the Euarthropoda, probably Crustacea. Also, among each of the major clades for which there are sufficient fossils for phylogenetic analysis, many stem lineages are present. In some cases, such as major groups within the Echinodermata, relatively high Linnaean rank has been accorded to these stem groups. In other cases, such as lobopods and arthropods from the Cambrian, considerable flux continues for many of the phylogenetic relationships, as the description of new fossils and the examination of older finds, though stem groups that have roughly equivalent morphological distinctiveness to those of the echinoderms have not generally been recognised with high Linnaean rank. It is apparent a remarkable degree of disparity arose at this time, whatever taxonomic approach is taken.

Sources & Further reading

1. Erwin, Douglas H., & Valentine, James W., 2013, The Cambrian Explosion: The Construction of Animal Biodiversity, Roberts & Co., Greenwood Village, Colorado.