Chitinozoa

Chitinozoans are bottle-shaped microfossils with hollow, organic-walled tests. They thrived during the Ordovician, Silurian, and Devonian periods and were exclusively marine. Tests occur singly, joined together in chains, and in clusters within organic cocoons; single tests result from the dissociation of tests in chains, and the breakup of cocoons. Chitinozoans may represent only parts of life cycles having planktonic and benthonic stages. Several conflicting opinions about chitinozoan affinities have been published yet the group's systematic position remains unknown; traditional placement of the Chitinozoa somewhere within the Protozoa has been challenged recently, and the case persuasively argued that chitinozoans may be metazoan eggs or egg capsules. The hypothesis is ventured here that chitinozoans are like reproductive bodies of graptolites. The usefulness of chitinozoans in stratigraphy is enhanced by their rapid evolution, wide diversity of form, and the short vertical ranges of many species. The lateral distributions of species are apparently independent of minor facies changes and many species are known from a wide variety of depositional environments. Numerous species are widely distributed on one or both sides of the North Atlantic and their dispersal across large areas of North America and northern Europe apparently was fairly rapid.