HISTORY OF CLASSIFICATION OF MESOZOIC AMMONITES

The ammonites were first subdivided at generic level on the basis of s hell coiling, heteromorphs or 'uncoiled' shells being separated after 1799 from the normally coiled shells. The latter were referred to a si ngle genus, Ammonites, until the late nineteenth century. After the pu blication of Charles Darwin's Origin of species in 1859, the more forw ard-looking workers adopted the ideal of a classification based on phy logenetic relationships; This necessitated the use of a wider range of characters. Increasing realization of the complexity of phylogenetic relationships brought a proliferation of names at lower taxonomic leve ls-genus and family. For a while, the belief that the growth stages of the shell provided a reliable key to ancestry dominated the work of s everal specialists. In the early twentieth century, Schindewolf favour ed reliance on a single character, sutural ontogeny, as the decisive c riterion in determining relationships. Other workers favoured a balanc ed appreciation of several characters. In the mid-twentieth century so me felt that the detailed lineages, of which glimpses are seen through the fossil record, might never be disentangled, and that classificati on at generic and specific level must often be arbitrary. Recently, mo re abundant material and better stratigraphical information have led t o the recognition of lineages based on closely-spaced assemblages whic h can be used as a basis for classification. The usefulness of the pre sent classification is briefly considered.