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

[Dann Pigdon <dannj@alphalink.com.au>]

Tim Williams writes: 

> Nevertheless, monotremes (both living and extinct) can be broadly divided into two categories: 'diggers' and 'swimmers'.

Unfortunately, platypus are also excellent diggers (since they nest in 
extensive burrow systems), thus demonstrating that a forearm adapted for 
digging isn't necessarily incapable of swimming (or vice versa). 

I'm not sure exactly how we'd extrapolate a swimming lifestyle for fossil 
monotremes known mainly from skull fragments, unless we assume that advanced 
electrosensors in the jaw are only of use to an aquatic animal (the 
electrosensing abilities of echidnas appear to be almost vestigial compared 
to those of the platypus). On the whole that may not be such a bad 
assumption - of course, just because most extant species that rely heavily 
on electrosensors seem to be aquatic doesn't mean that there weren't some 
extinct terrestrial species that also relied heavily on it. 

I wonder if a burrowing animal with poor eyesight would benefit from such a 
system? 

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Dann Pigdon
GIS / Archaeologist              geo cities.com/dannsdinosaurs
Melbourne, Australia             heretichides.soffiles.com
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