Phylogenetic biogeography with and without the fossil record: gauging the e¡ects of extinction and paleontological incompleteness

Biogeography played an important role in early developments in evolutionary theory and continues to play an important role in evolutionary studies and paleogeographic reconstructions. The development of a phylogenetic approach to biogeographic analysis has been important; however, fossil taxa have not always played a role in phylogenetic biogeographic studies and their role has been criticized by some phylogenetic biogeographers. Here, simulation studies are used to show that phylogenetic biogeographic studies on extant organisms that do not include fossil taxa can often be artificially incongruent and inaccurate. This is because area cladograms for extant taxa alone may differ from those that also include extinct taxa, implying different patterns of biogeographic relationship between areas, and area cladograms are the fundamental data of phylogenetic biogeographic analysis. This finding is analogous to what is known about how including fossil taxa in phylogenetic analyses along with extant taxa can improve resolution and accuracy. The incompleteness of the fossil record can also lead to artificial incongruence in phylogenetic paleobiogeographic studies because not all taxa that have ever lived are preserved in the fossil record, and thus those missing taxa cannot be incorporated into area cladograms. Therefore, area cladograms based on all preserved fossil species may also differ fundamentally from the true area cladograms which would be available if all taxa were preserved in the fossil record. Again, this can lead to artificial incongruence and inaccurate results. Simulations are used to show that under average preservational regimes for skeletonized marine invertebrates in the fossil record, and with average extinction probabilities, phylogenetic biogeographic studies of the extant biota are typically more likely to be artificially incongruent than those relying on fossil biotas. Further, in phylogenetic and biogeographic studies extant groups that have persisted for a very long time, have high extinction rates, and low diversity should be avoided. Phylogenetic biogeographic studies of fossil taxa should avoid groups with low diversity and a poor fossil record; these studies should also avoid time periods or regions with a poor fossil record. ß 2002 Published by Elsevier Science B.V.