zero to fully 100 per cent of the stratigraphic range of the ancestral species. For the
purposes of this argument I am assuming that we know both the true phylogeny and total
stratigraphic range of all the species. Clearly ghost ranges can be an artefact of cladistic
methods. I propose to call these artificial ghost ranges. On the other hand, ghost ranges
can arise from the imperfections of the fossil record. These I shall refer to as genuine
ghost ranges. Theoretically it is possible to detect a genuine ghost range, that is, a gap in
the fossil record. Figure 5.2A shows the true phylogeny of three fossil species with their
known stratigraphic ranges (thickened lines). Figure 5.2B identifies a minimum ghost
range that must be due to a gap in the record rather than an artefact of cladistic
methodology. Almost certainly, genuine ghost ranges occur in the fossil record. The
problem lies in distinguishing between artificial and genuine ghost ranges because we have
no way of knowing the true phylogenies of fossil species and hence whether or not a ghost
range has been produced purely by cladistic methods.
However, when discrepancies occur between known stratigraphic ranges of fossil
species and the inferred order of their occurrence deduced from cladistics, it seems to me
unwise to use the cladogram as a measure of the incompleteness of the fossil record,
because we know that cladistic methodology can produce artificial ghost ranges. We can
never know for certain whether we have discovered an artificial ghost range or a genuine
gap in the fossil record, but because cladistics can sometimes produce artificial ghost
ranges, cladograms cannot be used as a test of the completeness of the fossil record. On
the other hand, there are sound reasons for believing that the order in which species occur
in the fossil record is accurate (irrespective of the completeness or otherwise of the fossil
record; Paul 1982, 1985). Hence it is legitimate to use the order of occurrence of fossil
species as a test of inferred cladograms.
Figure 5.2 Diagrams illustrating one possible origin of real ghost ranges. A. Real phylogeny (solid
lines) with known stratigraphic occurrences (thickened). B. Corresponding real ghost range for
taxon B (broken line).
GHOST RANGES 95