A new phylogeny of iguanodontian is presented, based on a character matrix of 323 characters, over half of which are drawn from the postcranial skeleton. This was analyzed using both parsimony and time-calibrated Bayesian methods. These produce largely congruent results among Dryosauridae and Ankylopollexia, with two small groups among basal ankylopollexians: Iguanodontidae and an unnamed clade. The holotype of Mantellisaurus is recovered as the sister taxon to RBINS 1551, the holotype of “Dollodon”, supporting the suggestion that the latter is a junior subjective synonym of the former. In both analyses, Rhabdodontidae is expanded to include Tenontosaurus and Muttaburrasaurus. The topology in the basal portion of the tree (pectinate in the parsimony tree and bifurcating in the Bayesian tree) indicates that there is not a strong phylogenetic signal; more work is necessary to resolve this portion of the tree.
A method for incorporating juvenile specimens into a phylogeny with adult taxa is discussed. Ontogenetic sequences from taxa across the area of interest are examined, forming a phylogenetic bracket. For these taxa, juvenile specimens and adults are considered as separate OTUs, and characters which differ between juvenile and adult specimens for any taxon are considered ontogenetically sensitive characters. These characters are then coded as unknown for any OTU known only from juvenile specimens, as the adult state is unknown, and is likely to differ from the observed state in the juvenile. When this technique is used, juvenile specimens of Hypacrosaurus and Dryosaurus are recovered at the same node as their respective adult specimens. Orodromeus, however, is not, and substituting the juvenile specimen results in significant changes to the topology in that area. However, this is in the poorly resolved basal region of the tree. When there is a strong phylogenetic signal and a tree is reasonably well resolved, this method is able to accurately place juvenile specimens in a phylogeny. Doing so recovers the undescribed juvenile specimens from the Kirkwood Formation of South Africa as a Dryosaurid.
The biomechanics of the fused carpals and first digit of basal ankylopollexians is examined using Finite Element (FE) analysis. This fusion occurred concomitantly with a shift to quadrupedality, and an enlargement of the ungual of the first digit; this study explores whether either of these factors may have served as a driver of carpal-digit I fusion. The initial elements to fuse (the radiale and metacarpal I) may have helped distribute the load from a quadrupedal stance through metacarpal I in Camptosaurus. In the more derived Barilium, effective stresses are more evenly distributed under ungual loading than in Camptosaurus, largely due to the increased proximal-distal depth of the carpal block. Thus, there were likely multiple factors involved in the evolution of this enigmatic structure.
|Advisor:||Forster, Catherine A.|
|Commitee:||Carrano, Matthew, Clark, James M., Pyron, Alex, Weishampel, David|
|School:||The George Washington University|
|School Location:||United States -- District of Columbia|
|Source:||DAI-B 77/01(E), Dissertation Abstracts International|
|Subjects:||Evolution and Development, Paleontology, Systematic|
|Keywords:||Finite element analysis, Iguanodontia, Ontogeny, Ornithischia, Ornithopoda, Systematics|
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