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Journal of Paleontology 91(1):116–145
Table 1. Matrix of characters and character states for each taxon in the cladistic analysis. Genus species
1 2 3 45678 9101112131415
Pseudorthograptus obuti 000 0000 - 0 01100 ? Pseudorthograptus inoptinatus 010 0000 - 0 00100 - Hercograptus introversus 000 00000 1 11100 1 Pseudoretiolities? sp. 001 00100 1 1100 ? Pseudoretiolites perlatus 001 11102 1 11001 1 Pseudoretiolites hyrichos 002 01102 1 11001 1 Pseudopelgmatograptus obesus 212 02103 1 01001 1 Stomatograptus canadensis 211 12103 0 01001 1 211 12103 0 01000 1
Retiolites geinitzianus
Aeroretiolites cancellatus 012 12111 1 01000 0 Aeroretiolites? sp. 112 ? 2111 1 0000 - Rotaretiolites cf. exutus 112 22111 1 0001 - 112 22111 1 0001 - 0 1 1
Rotaretiolites exutus Eorograptus spirifer Paraplectograptus? sp. Paraplectograptus eiseli Sokolovograptus textor
1 1 1
2 2 2
0 0 3
2 2 2
1 1 1
? ? ?
3 3 3
0 0000 -
- - - -
? 01000 0 0 01020 0
112 32023 0 01120 0&1 1
1617181920 1 0000
1 0011 0 0
1 ? 00 1 ?
0 1100 0 1111 1 1100 0 1100 0 1100 0 1111 0 1111 1 0011 0 0011 0 1111 0 11 ?
0 1111 0 1111
? ? 0
or tree length. Bootstrap analyses were conducted using 1000 replicates. We also conducted a parsimony analysis on this matrix
using TNT (Tree Analysis using New Technology, see Goloboff et al., 2008). Using TNT it is possible to conduct a search using implied weighting (IW—rather than reiterative weighting as is done in PAUP*), which seeks to simultaneously maximize character consistency while minimizing tree length (e.g., Mitchell et al., 2013). In addition, TNT permits calculation of additional measures of node support, such as Bremmer support and relative Bremmer support.
Results and discussion of cladistic analysis.—Both the PAUP* and TNT analyses with all characters unweighted and unordered resulted in a single most parsimonious tree (MPT, Fig. 5.1). Analyses with weighted characters also produced single MPTs with the same topology. Although we experimented with a range of K values in the IW analysis (see Goloboff et al., 2008; Mirande, 2009), varations in K values produced no differences in the tree topology. A list of the character state changes at each of the nodes in the cladogram is included in Appendix 3. Acomparison of some of the tree statistics for the analyses using both unweighted and reweighted characters, as calculated from the PAUP* analyses, are: tree length, unweighted 51, weighted 22.3; consistancy index, unweighted 0.569, weighted 0.734; retention index, unweighted 0.722, weighted 0.835; homoplasy index, unweighted 0.431, weighted 0.266. Although the trees with unweighted characters were
resolved to a single MPT, the levels of support for most of the nodes was low. Only nodes 0, 1, 10, and 13 showed both bootstrap support >60% and Bremmer support >1. The analyses using reweighed characters in PAUP* and IW in TNT showed better support for many of the nodes (Fig. 5.1). Figure 6 shows a proposed phylogenetic tree based on the cladogram and the known stratigraphic ranges of the taxa. Several features are evident from these results. Despite the
inclusion of two different species of Pseudorthograptus that possess different tubaria forms and ancora depths, our results show that all of the taxa commonly included within the Retiolitinae (sensu Melchin et al., 2011) form a clade with relatively good support no matter which taxon is chosen as the
outgroup. Hercograptus introversus is sister to the retiolitine clade, as proposed by Melchin (1999). Our analyses show that species here assigned to
Hercograptus, Pseudoretiolites? sp. and Pseudoretiolites form a stem lineage for two sister clades, one including Pseudoplegmatograptus, Retiolites, and Stomatograptus, and the other including all other taxa in the study group. The latter clade, which includes our coded species of Paraplectograptus and Sokolovograptus, is almost certainly the root of the clade that includes all more derived “plectograptines” (Lenz and Melchin, 1997; Bates et al., 2005). There is support for the suggestion that Pseudoretiolites? sp. is primitive with respect to all other retiolitines. As noted above, there is some support for the
hypothesis of Lenz and Melchin (1997) that the species of Pseudoplegmatograptus, Retiolites, and Stomatograptus form a clade, which Lenz and Melchin assigned to the Retiolitinae. This contrasts with the results of Bates et al. (2005, fig. 8B), who found that those taxa formed a poorly resolved, paraphyletic group. Their analysis also showed Rotaretiolites branching from the near the base of the cladogram, sister to all of the other taxa normally included among the retiolitines. However, their analysis did not include the taxa here assigned to Aeroretiolites and Eorograptus and had some differences in character coding. To test whether the differences between our results and
those of Bates et al. (2005) are the result of inclusion of different taxa, differences in character coding, or both, we conducted an analysis in PAUP* using only the taxa that were in both our analysis and that of Bates et al. The only Llandovery taxon included in the Bates et al. analysis that was not included in ours was Dabashanograptus, which, in their analysis, occurred at a polytomy with Retiolites, Stomatograptus, and the more derived “plectograptines” (Bates et al., 2005, fig. 8B). The result of our analysis was a poorly resolved consensus of five MPTs (Fig. 5.2). This result indicates that although the addition of our new taxa to the analysis clearly helps to better resolve the relationships among the taxa in a manner more consistent with their known stratigraphic distribution (Figs. 5.1, 6), the differences in position of Rotaretiolites in the tree appear to be mainly the result of differences in character coding.
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