Telling the Evolutionary Time: Molecular Clocks and the Fossil Record

Chapter 5

Ghost ranges

Christopher R.C.Paul

ABSTRACT

Ghost ranges occur where phylogenetic reconstructions predict fossil ranges

beyond the known stratigraphic occurrence of the fossils. Cladistic methodology

refers all closest relationships to sister groups and assumes they arose at the same

time. Where the real relationship is ancestor-descendant, the ancestral taxon must

have existed for some time before the descendant taxon evolved and cladistic

analysis will produce an artificial ghost range. Alternatively, real ghost ranges are

caused by gaps in the fossil record. First records of fossil species can only occur in

the wrong order with respect to the true evolutionary order if the species

coexisted. Estimates indicate that at least 95 per cent of Phanerozoic fossil species did

not coexist at any time. This defines the minimum level of reliability of the

stratigraphic sequence of fossils, a result which is independent of the completeness

of the record. Discrepancies between stratigraphic occurrences of fossils and

predictions of cladograms are a valid test of the cladograms, not of the incompleteness

of the fossil record. If real ghost ranges were common, then first occurrences of

fossils would frequently move back in time as new, earlier occurrences were

detected. This provides a preliminary method for investigating the frequency of

real ghost ranges in the fossil record.

Introduction

Opinions differ as to the usefulness of stratigraphic data in reconstructing phylogenies. On
the one hand there are those who argue that stratigraphic data are irrelevant (e.g.
Patterson 1981). In contrast, Huelsenbeck and Ranala (1997) have published a maximum
likelihood method for deriving cladograms from stratigraphic data alone. Others (e.g.
Clyde and Fisher 1997; Smith 1994; Smith and Littlewood 1994; Wagner 1995, 1998)
argue that the best phylogenies derive from both stratigraphic data and character analysis.
Tests for congruence have been developed (e.g. Huelsenbeck 1994) and often suggest
close comparison between branching patterns in cladograms derived from character
analysis and the order of stratigraphic occurrence of fossils (e.g. Benton and Storrs 1994;
Benton and Simms 1995; Benton and Hitchin 1997; Hitchin and Benton 1997; Benton
1998). Norrell (1992) introduced the term ‘ghost taxa’ for taxa predicted by cladistics,