title: Phylogenetic analysis of 18S rRNA and the mitochondrial genomes of the wombat, Vombatus ursinus, and the spiny anteater, Tachyglossus aculeatus: increased support for the Marsupionta hypothesis.
abstract: The monotremes, the duck-billed platypus and the echidnas, are characterized by a number of unique morphological characteristics, which have led to the common belief that they represent the living survivors of an ancestral stock of mammals. Analysis of new data from the complete mitochondrial (mt) genomes of a second monotreme, the spiny anteater, and another marsupial, the wombat, yielded clear support for the Marsupionta hypothesis. According to this hypothesis marsupials are more closely related to monotremes than to eutherians, consistent with a basal split between eutherians and marsupials/monotremes among extant mammals. This finding was also supported by analysis of new sequences from a nuclear gene--18S rRNA. The mt genome of the wombat shares some unique features with previously described marsupial mtDNAs (tRNA rearrangement, a missing tRNA(Lys), and evidence for RNA editing of the tRNA(Asp)). Molecular estimates of genetic divergence suggest that the divergence between the platypus and the spiny anteater took place approximately 34 million years before present (MYBP), and that between South American and Australian marsupials approximately 72 MYBP.
authors.affiliation: Department of Genetics, Division of Evolutionary Molecular Systematics, University of Lund, Sölvegatan 29, S-223 62 Lund, Sweden. axel.janke@gen.lu.se
authors.forename: Axel
authors.initials: A
authors.lastname: Janke
authors.forename: Ola
authors.initials: O
authors.lastname: Magnell
authors.forename: Georg
authors.initials: G
authors.lastname: Wieczorek
authors.forename: Michael
authors.initials: M
authors.lastname: Westerman
authors.forename: Ulfur
authors.initials: U
authors.lastname: Arnason
mesh_terms: D000818:Animals; D001483:Base Sequence; D004272:DNA, Mitochondrial / Q000235:genetics*; D008394:Marsupialia / Q000145:classification / Q000235:genetics*; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D012337:RNA, Ribosomal, 18S / Q000145:classification / Q000235:genetics*; D012343:RNA, Transfer / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D004442:Tachyglossidae / Q000145:classification / Q000235:genetics*
chemical_list: D004272:DNA, Mitochondrial; D012337:RNA, Ribosomal, 18S; D012343:RNA, Transfer