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74 M. P. SMITH. P. C. J. DONOGHUE & I. J. SANSOM

Fig. 3. Stratigraphic distribution and phylogenetic relationships of Cambrian-Ordovician vertebrates, with the
biogeographic distribution of each group during the Ordovician indicated. Black bars indicate observed
occurrences, lines indicates inferred ghost ranges. Phylogenetic tree based on Donoghue et al. (2000) and
Donoghue & Smith (2001): Stratigraphic data from sources in Sansom et al. (2001) and Smith et al. (2001):
absolute ages of series and system boundaries from sources in Cooper (1999). Series abbreviations as in
Figure 2.