Year: 2006
Type: dissertation
Abstract: Increases in taxonomic sampling and the numbers and types of markers used in phylogenetic studies have resulted in a marked improvement in the interpretation of systematic relationships within Eutheria.However, relationships within several clades, including Paenungulata (Hyracoidea, Sirenia, Proboscidea), remain unresolved.Here the combination of i) a rapid radiation and ii) a deep divergence have resulted in limited phylogenetic signal available for analysis.Specifically i) a short internode separating successive branching events reduces the time available for changes to occur, while ii) the longer the time since divergence, the greater the opportunity for signal to be negatively affected by homoplasy.This is evident in both molecular and morphological data where an overall consensus on paenungulate relationships is lacking.Morphological analysis of anatomical and fossil evidence favours the association of Sirenia (S) and Proboscidea (P) (Tethytheria) to the exclusion of Hyracoidea (H); further, support for uniting these three taxa as Paenungulata is contentious.In contrast, molecular data provide strong support for Paenungulata but intra-ordinal relationships are ambiguous.Although results from mitochondrial DNA sequence data favour Tethytheria, there is no consensus of support for this clade from nuclear DNA.Nuclear DNA is typified by node instability but favours H+P in the largest concatenation of sequences.Due to the expected increased effect from homoplasy and consequently the increased likelihood for misleading signal, it is unclear which result is most likely to represent the "true" tree.An analysis of available and added intron sequences to characterise signal heterogeneity among nuclear DNA and mitochondrial DNA partitions indicated that the phylogenetic utility of partitions varies considerably.Subpartitioning of the data according to similar evolutionary processes/characteristics (e. g., mtDNA vs. nDNA and codon position) revealed new insights into the signal structure of the data set; specifically i) that nuclear DNA first codon positions, and to a lesser degree second codon sites, provide convincing support for H+P, and ii) that support for S+P by faster evolving sites within mtDNA suggests that this may be the result of misleading signal.If H+P represents the "true tree", then support for this clade indicates that phylogenetic signal has been reduced over Special thanks to Bettine, Conrad, Gauthier, Geeta, Krystal, Nico, Raurie, Sandi, Victor and Wilbur for much assistance in the laboratory and with analytical concerns, and to the members of the Evolutionary Genomics Group, who have come and gone over the past four years, for their support.Many thanks to Jurie van den Heever and other people in the department who I have come to know and who have helped in diverse ways.I am particularly indebted to Fengtang Yang and members of the Centre for Veterinary Science, Cambridge University, whose contribution to this study is invaluable.Many thanks to Johann Watson with attempts to catch aardvarks.A very big thanks to Hanneline and Mhairi for their fantastic support in the last few months and to Sands, Kate, Big Rich, Mhairi, Brent, Victor, Savel and Geeta for much needed discussions and trips to the Neelsie.
Author: Amanda T. Pardini
Language: English
Subfield: Paleontology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
Funder: Harry Crossley Foundation
OpenAlex ID: W148629553