Re: Platypuses may be older than we think...

[evelyn sobielski <koreke77@yahoo.de>]

> Given the limited number of extant montotreme
> morphotypes (namely two), it's 
> not surprising that fossil monotremes have been
> shoe-horned into 'platypus' 
> or 'echidna' camps. Who knows what variations in
> form extinct monotremes may 
> have toyed with? It's like trying to classify fossil
> placental mammals if 
> only primates and antelope still existed (anything
> with hooves was a 
> proto-antelope, anything with fingers a
> proto-primate!). Our modern points 
> of comparison for monotremes are some-what limited.

I cannot help thinking of Presbyornithidae, which has
had a somewhat meteoric rise from "transitional
shorebirds" to near-proof that 4+ Anseriformes
lineages (3 crown, at least 1 stem) must have been
distinct already by 65 mya.

In any case, David's idea that echidnas are
secondarily terrestrial is interestng and would need
to be dismissed.

But such a more recent split would be expected to
leave an imprint on anatomy/osteology, notably
limbs/shoulder/pelvis. Someone competent in mammalian
osteology might be able to give some insight. I cannot
contribute anything on this, except the observation
that echidna forelimbs are adapted in a fairly
generalized way to digging and scratching, and that
the hindlimbs seem autapomorphically modified in a
peculiar way that does not seem incompatible with
secondary terrestriality at least at first glance.

In any case, having _Megalibgwilia robusta_
(=_Zaglossus robustus_) in the ?mid-late Miocene?
quite obviously would constrain the time for a more
recent echidna-platypus split:
http://www.parks.sa.gov.au/publish/groups/public/@parks/@uppersoutheast/documents/all/005136.gif


Regards,

Eike


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