[Taxacom] phylogeny (Monotremata)

[Stephen Thorpe]

Hi Alex,
Yes, you are undoubtedly correct about the details of mammal evolution making the case more complex. Nevertheless, I was thinking more about the general simple schema of saying something like: group G can be split into those with character C (e.g. giving birth to live young), and those with alternative C' (e.g. laying eggs), and for this reason those with C' are the sister group to those with C. To a beginner in phylogeny, I imagine that this could give a seriously misleading impression!
Cheers, Stephen

From: Alex Borisenko <aborisen at uoguelph.ca>
To: Stephen Thorpe <stephen_thorpe at yahoo.co.nz>
Cc: taxacom <taxacom at mailman.nhm.ku.edu>
Sent: Wednesday, 10 August 2011 2:24 AM
Subject: Re: [Taxacom] phylogeny (Monotremata)

Hi Stephen,

I am afraid that part of the problem is that 'mammalisation' of theriodonts was a largely parallel process that happened with complete disregard to the principles of monophyly, e.g., see Tatarinov (1976). Most key mammalian traits appeared gradually and independently in different theriodont lineages of which monotremes and therian mammals are the only ones alive. The key difference from 'amphibians' and 'reptiles' is that mammals are less 'basal' to all other vertebrates. Just like the former two groupings, 'mammals' is a highly operational 'common sense' term and should not be abolished just because it is not a perfect fit to the present day cladistic-driven nomenclatural paradigm. If you look at mammals as a gradistic grouping, the phrase below has only minor logical flaws. I would remove the statement 'for this reason' and would say "all other *living*" mammals. My two cents...

Best wishes,
Alex




On 08/08/2011 11:47 PM, Stephen Thorpe wrote:
> increasingly, I get the impression that the basic principles of phylogeny are not well understood
> 
> look at the first paragraph here: http://www.ucmp.berkeley.edu/mammal/monotremesy.html
> 
>> Monotremes are mammals. Unlike other mammals monotremes lay eggs, as did the ancestors of the mammals. For this reason, the Monotremata are considered the sister group to all other mammals.<
> 
> Surely, this is badly expressed, or even just plain wrong? The reason why Monotremata (or at least the extant lineage thereof) are considered to be the sister group to all other mammals is because they are monophyletic (by virtue of having synapomorphies), in addition to being basal to (outside of) the main mammal clade (by virtue of laying eggs - a plesiomorphy) ...
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