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Re: transitional fossils



If we can come up with a good fossil record of monotremes in the next 50 years, perhaps within our lifetimes we will finally have some idea what the PT definition really means. :-)
According to some phylogenies, this definition would exclude triconodonts, multituberculates, and symmetrodonts (while other phylogenies would include some of all of these groups).
In the meantime, I'm sticking with an osteological diagnosis that is useful now. If I had to cladistically anchor mammals (which thankfully I don't), I would use sinoconodonts or morganucodonts long before I would anchor mammals on monotremes (crown clades aren't all that useful for vertebrates, and this one is particularly vague).
-------Ken Kinman
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The mammalian border is clearly defined in PT. Mammalia begins with the most recent common ancestor of Monotremata, Marsupialia, and Eutheria. (Note I said clearly defined, not clearly diagnosed ...)

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