The Early Radiation of Cambrian Sponges from Guizhou, South China  

Since sponges are the most primitive group of multicellular animals, it is logical that they should have a long fossil record.  Well-preserved sponge fossils are common in early Cambrian black shales throughout China, and elucidate the detailed mechanics of the “Cambrian Explosion” and the early radiation of sponges. 

We examined sponges from the Lower Cambrian Niutitang Biota and the Middle Cambrian Kaili Biota, Guizhou.  40 distinct genera are known from the Niutitang Biota.  In addition to cnidaria, arthropods, algae, and molluscs, sponges are the dominant group, comprising 55% of the genera-level diversity.  The Leptomitidae (Demospongea) are the dominant sponges.  The abundance of well preserved sponges in this Early Cambrian Formation suggests that the sponges had already undergone an explosive radiation by the end of the Qiongzhusian stage; sponges must have relatively abundant shortly after the Precambrian-Cambrian boundary. 

The Kaili Biota is of earliest Middle Cambrian age.  It preserves seven sponge genera, which comprise a mere six percent of the biota.  As in the Niutitang, Demospongea dominate sponge diversity in the Kaili: six genera belonging to the Demospongea, with the only other genus representing Hexactinellida.  The Kaili sponges increase our knowledge of early sponge diversity, and provide an important record of sponges from the Middle Cambrian of China.