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Jurassic Araucarian:


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Phylogenetic/Stratigraphic Congruence

Measures of phylogenetic/stratigraphic congruence for the Araucariaceae utilizing the statistical tests, fossil taxa, and phylogenies described above were surprisingly low.

The range of MSM* values obtained for the sectional relationships within Araucaria is 0.51-0.84 for the classical phylogenetic hypothesis (Gilmore and Hill 1997, figures 3a, 4a, 4c and 4d; Setoguchi et al. 1998, figure 1) (Figure 3.1, 3.3), and 0.5-0.67 for the alternative one (Gilmore and Hill 1997, figures 3b, 4b) (Figure 3.2-3.3). These relatively low values are probably related to the incongruence between the FAD ranges of the sections and their position on both tree topologies (Figure 3.1-3.2), generating a long temporal ghost for some lineages. Alternatively, the broad MSM* range obtained with the FAD dates used in this study may reflect the high degree of uncertainty in determining the precise ages of most of the sections. For example, the Lower Cretaceous FAD range for Section Intermedia covers about 43 million years. Another potential problem is the lack of fossil taxa as terminals in the phylogenetic analyses that were utilized.


Ideally, a clade with a rich fossil record and a well-resolved phylogenetic hypothesis should show high levels of congruence among these data sets. The Araucariaceae would seem to satisfy the requirements for high phylogenetic/stratigraphic congruence, as the family is considered to have a particularly long and rich fossil record, and substantial living diversity to provide abundant data for phylogenetic studies. Nevertheless, the analysis presented here indicates that much more research is needed, probably in both areas, to provide a more consistent estimate of this important conifer family's evolutionary history. This will most likely entail the continued discovery and description of new fossils as well as a critical re-evaluation of known fossil taxa. In addition, it is likely that phylogenetic studies based only on extant taxa underestimate the true complexity of araucarian phylogeny, as the fossil record indicates high levels of extinct diversity, including completely extinct sections (e.g., Yezonia) with unique character combinations (Ohsawa et al. 1995). The inclusion of well-preserved and reconstructed fossil taxa in a combined analysis of the Araucariaceae should provide new data regarding those parts of the phylogeny currently represented by ghost lineages leading to a more robust phylogenetic hypothesis and improved phylogenetic/stratigraphic congruence.

Regardless of the causes of the current phylogenetic/stratigraphic incongruence for the Araucariaceae, the bract/scale complex described here is significant as the first bona fide megafossil of the Araucariaceae from the Newark Supergroup and one of the few early Mesozoic examples from all of North America. This fossil is also significant as the earliest record of Araucaria section Eutacta. Although plant fossils have been known from the Newark Supergroup for many years, there is little question that it remains an underutilized source of information regarding early Mesozoic plant evolution.


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Jurassic Araucarian
Plain-Language & Multilingual  Abstracts | Abstract | Introduction | Materials and Methods
Description and Comparisons | Discussion | Acknowledgements | References
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