Evolutionary scenario of the early history of the animal Kingdom: Evidence from Precambrian (Ediacaran) weng’an and early Cambrian Maotianshan biotas, China

Abstract

Late Proterozoic (Ediacaran) Weng’an (580 mya) and Early Cambrian Maotianshan (c. 530 mya) faunas of South China, illustrated here, document diverse body plans at phylum and subphylum level and confirm that bilaterians evolved well before the “Cambrian explosion”. The Weng’an faunas (from Guizhou), the oldest record of metazoans, consist mainly of embryos with possible affinities to living sponges, cnidarians, and bilaterians, but with adult specimens (though microscopic) of the same groups. The Maotianshan Shale faunas (from Yunnan), remarkably diverse at species level (over 100 species), have great diversity of metazoan body plans, many comparable with those of living groups. Because they occur at or near the evolutionary roots of many animal groups, intermediate forms are present. Evolution of Early Cambrian metazoans was surprisingly rapid. Worm-like ancestral euarthropods elucidate the evolutionary origins of the arthropods. The diverse Maotianshan vertebrates, representing “missing” history between an amphioxus-like ancestor and craniate vertebrates, provide an improved understanding of the early evolution of the vertebrates.