There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
Morphological and molecular data are currently contradictory over the position of
monotremes with respect to marsupial and placental mammals. As part of a re-evaluation
of both forms of data we examine complete mitochondrial genomes in more detail. There
is a particularly large discrepancy in the frequencies of thymine and cytosine (T-C)
between mitochondrial genomes that appears to affect some deep divergences in the
mammalian tree. We report that recoding nucleotides to RY-characters, and partitioning
maximum-likelihood analyses among subsets of data reduces such biases, and improves
the fit of models to the data, respectively. RY-coding also increases the signal on
the internal branches relative to external, and thus increases the phylogenetic signal.
In contrast to previous analyses of mitochondrial data, our analyses favor Theria
(marsupials plus placentals) over Marsupionta (monotremes plus marsupials). However,
a short therian stem lineage is inferred, which is at variance with the traditionally
deep placement of monotremes on morphological data.