 The earliest fossils possessing features typical of fungi date to the Paleoproterozoic era, some 2,400 million years ago; these multicellular benthic organisms had filamentous structures capable of anastomosis.Classically, the boundary between the Proterozoic and the Phanerozoic eons was set at the base of the Cambrian Period when the first fossils of animals, including trilobites and archeocyathids, as well as the animal-like "Caveasphaera", appeared.In the second half of the 20th century, a number of fossil forms have been found in Proterozoic rocks, but the upper boundary of the Proterozoic has remained fixed at the base of the Cambrian, which is currently placed at 541 Ma.