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A Phylogenetic Analysis of the Basal Ornithischia (Reptilia, Dinosauria)
| Title: | A Phylogenetic Analysis of the Basal Ornithischia (Reptilia, Dinosauria) |
| Author: | Spencer, Marc Richard |
| Description: | The placement of Lesothosaurus diagnosticusand the Heterodontosauridae within the Ornithischia has been problematic. Historically, Lesothosaurushas been regarded as a basal ornithischian dinosaur, the sister taxon to the Genasauria. Recent phylogenetic analyses, however, have placed Lesothosaurusas a more derived ornithischian within the Genasauria. The Fabrosauridae, of which Lesothosauruswas considered a member, has never been phylogenetically corroborated and has been considered a paraphyletic assemblage. Prior to recent phylogenetic analyses, the problematic Heterodontosauridae was placed within the Ornithopoda as the sister taxon to the Euornithopoda. The heterodontosaurids have also been considered as the basal member of the Cerapoda (Ornithopoda + Marginocephalia), the sister taxon to the Marginocephalia, and as the sister taxon to the Genasauria. To reevaluate the placement of these taxa, along with other basal ornithischians and more derived subclades, a phylogenetic analysis of 19 taxonomic units, including two outgroup taxa, was performed. Analysis of 97 characters and their associated character states culled, modified, and/or rescored from published literature based on published descriptions, produced four most parsimonious trees. Consistency and retention indices were calculated and a bootstrap analysis was performed to determine the relative support for the resultant phylogeny. The Ornithischia was recovered with Pisanosaurusas its basalmost member. A monophyletic Genasauria was recovered with two major clades: Eocursor+ Cerapoda and Fabrosauridae + Thyreophora. Lesothosauruswas recovered within the Fabrosauridae, along with a clade consisting of Stormbergia+ Agilisaurus. The Heterodontosauridae was recovered as the basalmost taxon of the Cerapoda. In the bootstrap analysis, however, several taxa, including the Fabrosauridae, collapse down to form a polytomy at the base of the Genasauria consisting of Eocursor, Lesothosaurus, Stormbergia+ Agilisaurus, Cerapoda, and Thyreophora. This analysis is the first to recover a weakly-supported Fabrosauridae clade, and lends further support to the placement of the Heterodontosauridae within the Cerapoda, but outside of the Ornithopoda. Additionally, the implication of the phylogenetic relationship of Eocursorand the Cerapoda indicates, paleobiogeographically, that they evolved in the southern supercontinent of Gondwana in present-day southern Africa. |
| Permanent Link: |
http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1185914798
http://hdl.handle.net/2374.OX/15556 |
| Date: | 2007 |
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