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

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

Tim Williams writes: 

> Dann Pigdon wrote: 
>
> > It depends on exactly what *Kryoryctes cadburyi* was. I've found at least
> > one phylogeny that places it within Tachyglossa: 
> >
> > http://www.fmnh.helsinki.fi/users/haaramo/metazoa/Deuterostoma/Chordata/Syna
> > psida/Basal_Mammalia/Prototheria.htm
>
> Little _Kryoryctes_ was certainly a digger (hence the name).  But it's a stretch to say therefore it was a tachyglossan.  BTW, I'm not saying that's what you're saying, Dann; but it may be the reason behind why that website classifies _Kryoryctes_ as a tachyglossan (albeit with a '?').  I think there's a _National Geographic_ article that also alludes to it being a Cretaceous echidna.

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. 

*Steropodon* has been called (and artistically depicted as) a 'Cretaceous 
platypus' for years, despite the only similarity being in general tooth 
form. Even that similarity seems tenuous - Steropodon's permanent teeth look 
a bit like the deciduous milk teeth of the platypus (IIRC). That certainly 
suggests that the two are related in some way, but 'related in some way' and 
'direct decendant' aren't necessarily the same thing. I'd want something 
more than a jaw fragment before calling *Sterpodon* a bona-fide platypus (or 
proto-platypus). 

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