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Stylophoran supertrees revisited

100%

Lefebvre B.

Acta Palaeontologica Polonica

2005

tom 50

nr 3

Supertree analysis is a recent exploratory method that involves the simultaneous combination of two or more character−based source trees into a single consensus supertree. This method was recently applied by Ruta to a fossil group of enigmatic Palaeozoic forms, the stylophoran echinoderms. Ruta’s supertree suggested that mitrates are polyphyletic and originated from paraphyletic cornutes. Re−examination of Ruta’s data matrix strongly suggests that most source trees were based on dubious homologies resulting from theory−laden assumptions (calcichordate model) or superficial similarities (ankyroid scenario). A new supertree analysis was performed using a slightly corrected version of Ruta’s original combined matrix; the 70% majority−rule consensus of 24,168 most parsimonious supertrees suggests that mitrates are monophyletic and derived from paraphyletic cornutes. A second new supertree analysis was generated to test the influence of the pruning of three taxa in some calcichordate source trees; the 70% majority−rule consensus of 3,720 shortest supertrees indicates that both cornutes and mitrates are monophyletic and derived from a Ceratocystis−like ancestor. The two new supertree analyses demonstrate the dramatic influence of the relative contributions of each initial assumption of plate homologies (and underlying anatomical interpretations), in original source trees, on the final topology of supertrees.

A species-level supertree for stylophoran echinoderms

100%

Ruta M.

Acta Palaeontologica Polonica

2003

tom 48

nr 4

The construction of supertrees from smaller, character−based cladograms permits simultaneous inclusion of a large number of taxa in a single analysis, summarizes patterns of relationships from many independent data sources, and highlights areas of conflict to be targeted by character matrix studies. The method is applied for the first time to stylophoran echinoderms (cornutes and mitrates). Published cladistic analyses of this problematic group are used to build a supertree of 77 species. Key areas of stylophoran phylogeny to be addressed by future studies include the systematic placement of several mitrate−like cornutes, the affinities of peltocystidan and lagynocystid mitrates, and the position of such bizarre−looking taxa as Diamphidiocystis and Lobocarpus. A strict consensus of 72,278 equally parsimonious supertree solutions shows cornutes to be paraphyletic relative to mitrates. Lobocarpusis either one of the most derived cornutes or the sister taxon to all mitrates, in agreement with its chimaera−like combination of cornute− and mitrate−like features. Chinianocarpos is basal to peltocystidan rather than to mitrocystitidan mitrates. Nanocarpus, an almost bilaterally symmetrical taxon previously allied to cornutes, is nested within mitrates as sister taxon to mitrocystitids plus anomalocystitids. Diamphidiocystis and Lagynocystis cause loss of phylogenetic resolution among derived mitrocystitids and basal anomalocystitids.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

1 Lefebvre B.

1 Ruta M.

1 2005

1 2003

Wyniki wyszukiwania

Stylophoran supertrees revisited

A species-level supertree for stylophoran echinoderms