Addendum (Re: LATE SURVIVING CYNODONT)

[Pieter.Depuydt@rug.ac.be]

Today I found something in the 5 June issue of Nature, which is an 
interesting addendum to the monotreme question/answer:


Investigation of mitochondrial DNA sequences of the platypus and an 
Australian kangaroo species (Macropus robustus or wallaroo), strongly 
supports the position of the platypus on the marsupial lineage, or 
in cladistic terms: platypus and the marsupials shear a more recent 
common ancestor than each with placental mammals. If I understand 
correctly, this means Theria has to be redefined, as in the light of 
the current evidence, Theria (Marsupialia and Placentalia) is 
paraphyletic.
This also suggests that the view of monotremes as being 
'primitive' as reflecting the ancestral state and not having 
developed the 'advanced' features of the other mammals
should give way to the vision that considers the characteristics of the 
Australian mammals as adaptations to specific environments that have 
been existing in Australia, for example harsh conditions with periods 
of prolonged drought.
There goes another 'living fossil'....

References:

Penny and Hasegawa: Molecular systematics: The platypus put in its 
place (News and Views), Nature 387, p549 (1997).
Janke et al. J. Mol. Evol 42, 153-159 (1997).
Janke et al. Proc. Natl. Acad. Sci USA 94, 1276-1281 (1997).