Systematic Zoology Advance Access published online on July 3, 2009
Systematic Zoology, doi:10.1093/sysbio/syp029
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© Society of Systematic Biologists
Testing the Impact of Miniaturization on Phylogeny: Paleozoic Dissorophoid Amphibians
1 Redpath Museum, McGill University, 859 Sherbrooke Street West, Montreal, QC, Canada H3A 2K6 ; E-mail: nfrobisch@uchicago.edu
2 Present address: Department of Organismal Biology and Anatomy, Culver 106, University of Chicago, 1027 East 57th Street, Chicago, IL, 60637, USA
3 Staatliches Museum für Naturkunde, Rosenstein 1, D-70191 Stuttgart, Germany; E-mail: schoch.smns{at}naturkundemuseum-bw.de
* Correspondence to be sent to: Department of Organismal Biology and Anatomy, Culver 106, University of Chicago, 1027 East 57th Street, Chicago, IL, 60637, USA; E-mail: nfrobisch{at}uchicago.edu
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Abstract |
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Among the diverse clade of Paleozoic dissorophoid amphibians, the small, terrestrial amphibamids and the neotenic branchiosaurids have frequently been suggested as possible antecedents of either all or some of the modern amphibian clades. Classically, amphibamids and branchiosaurids have been considered to represent distinct, but closely related clades within dissorophoids, but despite their importance for the controversial lissamphibian origins, a comprehensive phylogenetic analysis of small dissorophoids has thus far not been attempted. On the basis of an integrated data set, the relationships of amphibamids and branchiosaurids were analyzed using parsimony and Bayesian approaches. Both groups represent miniaturized forms and it was tested whether similar developmental pathways, associated with miniaturization, lead to an artificial close relationship of branchiosaurids and amphibamids. Moreover, the fit of the resulting tree topologies to the distribution of fossil taxa in the stratigraphic rock record was assessed as an additional source of information. The results show that characters associated with a miniaturized morphology are not responsible for the close clustering of branchiosaurids and amphibamids. Instead, all analyses invariably demonstrate a monophyletic clade of branchiosaurids highly nested within derived amphibamids, indicating that branchiosaurids represent a group of secondarily neotenic amphibamid dissorophoids. This understanding of the phylogenetic relationships of small dissorophoid amphibians provides a new framework for the discussion of their evolutionary history and the evolution of characters shared by branchiosaurids and/or amphibamids with modern amphibian taxa.
Keywords: amphibamids; Bayesian analysis; branchiosaurids; dissorophoids; fossil taxa; Lissamphibia; miniaturization; parsimony analysis; Paleozoic; stratigraphic consistency
Received October 23, 2008; Revised February 22, 2009; Accepted May 6, 2009