Abstract

It is still an enigma of just what triggered the development of multicellular animals, the metazoans. The rise of oxygen has commonly been suggested as the cause, which probably had a marked effect. But why do the metazoans seem to appear in the fossil record, with some diversity, in the late Neoproterozoic around 575–580 million years ago? Perhaps the sudden appearance is related to a rapid expansion of metazoans into global oceans as they became markedly less saline with the deposit of saline giants in the Neoproterozoic. Metazoans may well have developed first in ‘cold cradles’ in deltaic and estuarine conditions earlier, when seas were more saline, and with the removal of salts from the global oceans, the seas became their ‘global playgrounds’ and with this invasion the fossil record improved significantly. Such an idea can only be tested with more precise dating of the saline giants themselves.