INTRODUCTION

My interest in taking up the subject of the post-mortem dispersal of cephalopod shells in 1957 came from a review and critique by Jaworski (1940) in Neues Jahrbuch of an article by G. Scott (1940) in which a palaeoenvironmental model for Texan Cretaceous ammonites was put forward. Jaworski (1940) pointed out the illogicality of a 'palaeohistory' for chambered shells as though they were gastropods. Scott did cite, however, a few records of the nekroplanktonic transport of empty nautilus shells in his discussion. In the analysis of the post-mortem dispersal of cephalopod shells we are not concerned with organisms as such, but with the passive distribution of "objects" by oceanic currents, and hence under conditions defined in a different medium from that occupied by the living animal. The opinions of workers in the field have centred around attempts at relating shell-forms to specific activities extending as far as to drawing conclusions about cephalopod shells as environmental indicators, as opposed to factors relating to the post-mortem dispersal of the shells. From the standpoint of the palaeontologist, the fundamental issue concerns what happened to the empty shell after the death and decay of the animal.

Since the appearance of my original contributions from 1958 to 1986, I have followed developments in the field of the distribution of fossil cephalopod shells. An observation arising out of this research is that in some cases, 'the wheel keeps getting rediscovered', as it were. There is a source of uncertainty, namely, the confusion occasioned by failing to accept that what the ammonites and nautiloids did in life has little or nothing to do with what happened to them after death. After all, the history of pieces of wood that float up onto beaches has little to do with where the trees from whence they derive once lived.

The following assumptions provide a convenient basis for discussion:

1. Various dead chambered shells would have been amenable to palaeoflumenological dispersion, to use the term introduced by Kobayashi (1954).
2. An unspecified number of shells with specific morphological characteristics, with a benthic mode of life, may have remained near, or close to, where they died.
3. Some shell-types lent themselves to a short period of nekroplanktonic dispersal, before sinking. Others could remain afloat for long periods.

The cases reviewed here may be conveniently considered in the following order. Firstly, the information available for the paradigm, the pearly Nautilus, secondly, extrapolation to the ammonites and, thirdly, the case represented by some Palaeozoic nautiloids (orthocones, cyrtocones, etc.).