Re: LATE SURVIVING CYNODONT (lenghty and boring)

[Ron Dass <radass@orion.neca.com>]

Pieter - Your reply is much appreciated; legnthy perhaps, but not boring.
Though I did have to dig out an old zoology textbook to understand it,
it was well worth it.

you wrote:
>Another example: the transition from the primitive articular-quadrate jaw
hinge to the 
>mammalian dentary-squamosal articulation went via a series of 
>intermediate forms who possessed a double hinge (Probainognathus, 
>Pachygelenus,...)

I believe this is the "two part" jaw I referred to in my post. Yes? 
Is the posterior part of this double hinge homologous to one of the middle
ear bones (hammer, anvil, stapes) in advanced mammals?


I was surprised at the finding of a close relationship between monotremes
and marsupials, partly for the reasons stated by dinogeorge, ie. that 
viviparity would have to have evolved twice separately, though this isn't
such a big deal. After all, viviparity evolved in several separate reptile
lines (NZ skinks(?), NZ geckoes, and several snake families)

Of greater concern were other "reptile-like" traits that would seem to distance
monotremes from all other mammals.In particular, I'm not at all sure about
this, so someone help me out, I think I read somewhere that monotreme means
"one hole" and refers to the fact that the platypus has a cloaca rather than
the separate anus and penis/vagina characteristic of other mammals (hope the 
communications decency police don't smash down my door ;-). Is this true?
And do monotremes excrete uric acid like birds and my geckoes or urea like me?
The answer to that might indicate a broad physiological gulf between monotremes
and other mammals, much more so than viviparity.

Incidently, are any fossil monotremes known that are generalist "normal"
herbivores and carnivores or are they all highly specialized wierdos
like the platypus and echidna. For example, were multituberculates monotremes or
monotreme-like?


                                still an amateur
                                Ron Dass