Skip to navigation | Skip to content  Debate over platypus and
kangaroo link  Don Colgan  Don Colgan - debate not over yet
(Pic: Australian Museum.  A new US study that debunks the
relationship between the kangaroo and the platypus is unlikely
to settle an age-old debate, says an Australian expert.  The
study published in the July 1 issue of the journal Mammalian
Genome strongly supports the "Theria" hypothesis that marsupials
such as the kangaroo are more closely related to mammals such as
humans, who bear live young, than to egg-laying mammals
(monotremes) such as the platypus.  The competing "Marsupionta"
hypothesis, which links marsupials and monotremes as the more
closely related sister groups, has been supported by analysis of
mitochondrial DNA - the same method used to link whales and
hippos.  Mitochondrial DNA has traditionally been easier to
access and has the advantage of not undergoing recombination as
does nuclear DNA. A downside, however, is that it is a
relatively small sample of the genome.  Th