Cambrian fauna

Cambrian fauna

Of those modern animal phyla that fossilize easily, all save the bryozoans appear to have representatives in the Cambrian, and of these most (except the considerably older sponges) seem to have originated near the start of the period. Many extinct phyla and odd animals that have unclear relationships to other animals also appear in the Cambrian. The apparent "sudden" appearance of very diverse faunas over a period of no more than a few tens of millions of years is referred to as the "Cambrian Explosion". Also, the first possible tracks on land, such as Protichnites and Climactichnites, dating to about 530 mya and found in Ontario, Canada, and northern United States, appeared at this time. The conodonts, small predatory primitive chordates known from their fossilised teeth, also appeared during the Furongian epoch of the Cambrian period. The conodonts thrived throughout the Paleozoic and the early Mesozoic until they completely disappeared during the Late Triassic period when the first mammals were evolving.
The best studied sites where the soft parts of organisms have fossilized are in the Burgess shale of British Columbia. They represent strata from the Middle Cambrian and provide us with a wealth of information on early animal diversity. Similar faunas have subsequently been found in a number of other places — most importantly in very early Cambrian shales in the People's Republic of China's Yunnan Province (see Maotianshan shales). Fairly extensive Precambrian Ediacaran faunas have been identified in the past 50 years, but their relationships to Cambrian forms are quite obscure.