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EARLY PALAEOZOIC VERTEBRATE BIOGEOGRAPHY 75

Fig. 4. Stratigraphic distribution and phylogenetic relationships of Cambrian-Silurian vertebrates, with the
biogeographic distribution of each group during the Silurian 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 Blieck & Janvier (1991), Janvier (1996a),
Sansom et al (2001), Smith et al. (2001) and other sources discussed in the text; absolute ages of series and
system boundaries from sources in Cooper (1999). Series abbreviations as in Figure 2.