Re: Platypus (was Re: Ratites)

sarima@netcom.com (Stanley Friesen) writes:
>
>--- Platypuses are probably closer to multuberculates than
>to *any* placental or marsupial.
>--

I am curious as to what evidence you have to support this idea.  As
far as I can tell there is still considerable debate on this topic
and that there is probably less evidence for a monophyletic group
comprised on monotremata+multitubercualta  than for alternative
hypotheses.  Hypotheses that do not result in monotremes being
closer to multitubeculates include those that have multituberculates
outside of a monphyletic monotremes+therians and those that have
multitubeculates as a sistertaxa to therian to the exclusion of
monotremes.

As Rowe (1988) notes  (p. 251)
   "For some time, Multituberculata was allied with Monotremata in
   'Prototheria' (e.g., Hopson, 1970; Kermack and Kielan-Jaworowska,
   1971; Kermack and Kermack, 1984).  More recently, however,
   interpretation of the characters diagnosing the group has
   been questioned (e.g. Griffiths, 1978; Presley, 1981; Kemp,
   1983; Clemens, 1986; Kielan-Jaworowska et al., 1986) and many
   workers have now rejected Prototheria, although the position
   of Multituberculata has remained uncertain."

Rowe's analysis supports Multituberculata as being closer to
Therians than either is to Monotremata.  This would leave
platypi as equally related to multituberculates, marsupials,
and placentals.

Rowe, T, 1988, Definition, diagnosis and origin of Mammalia,
  Journal of Vertebrate Paleontology, 8(3): 241-264.

In addition, Archer et al. (1985) in their description of
_Steropodon galmani_, a Cretaceous platypus-like
monotreme from Australia,
suggest that the dental morphology of _Steropodon_, supports
the idea that Montotremes are actually therians.

Archer, M, Flannery, TF, Ritchie, A, and Molnar, RE, 1985,
  First Mesozoic mammal from Australia--an early Cretaceous
  monotreme, Nature 318:363-366.

Rick Toomey
Illinois State Museum
toomey@museum.state.il.us
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