Re: Monotremes and Jurassic mammals -- where do they fit in the tree of life?

pnyikos wrote:
On Apr 28, 1:10 am, John Harshman <jharsh...@xxxxxxxxxxx> wrote:
pnyikos wrote:
On Apr 26, 6:41 pm, John Harshman <jharsh...@xxxxxxxxxxx> wrote:
pnyikos wrote:
On Apr 26, 10:52 am, John Harshman <jharsh...@xxxxxxxxxxx> wrote:
pnyikos wrote:
On Apr 24, 10:41 am, John Harshman <jharsh...@xxxxxxxxxxx> wrote:
pnyikos wrote:
John Harshman wrote:
And doubtless there would be some
other term for anything more closely related to Morganucodon than to
Marmota.
Not if ranks were abolished. How would you quantify "more closely
related"?
Surely you know this if you just think about it.
I have known since childhood that the Linnean classification has a
way. Your suggestions below are flawed.
You have known wrong. Arbitrary dividing lines don't do a good job even
of quantifying similarity, much less relationship.
The word "arbitrary" is extremely ambiguous. Put it this way: the
fewer and more insignificant the apomorphies, the smaller the Linnean
taxon. Thus the hypothetical young digger could be quite
communicative ("within error bars" to use an expressiion familiar to
you) if he said, "these morganucodonts are in the same subfamily as
Morganucodon, whereas the examples YOU name aren't even in the same
infraclass."
I've asked you several times for the criteria you use to assign ranks to
taxa. No response so far. How few is few? How insignificant is
insignificant? How small is small?
I'm sure the systematists of old had a very good feel for this kind of
thing--just from a lifelong interest in the various Linnean taxa.
It's obvious, for instance, that the shoulder girdle of the platypus
should weigh far, far more in the classification than a dozen or so
mitochondrial genes.
"It's obvious" is a code for "I can't justify it".

These were presumably what led one article to classify it in a clade
with marsupials that excluded placentals. We've talked about this
before, and you agreed we shouldn't put too much faith in such
analyses.
Note that this has nothing to do with ranks, which is what you're
supposed to be telling me about. Do you really not notice when you're
going off the rails?

Apparently not.

Where the shoulder girdle is concerned, I'm not just talking about the
disappearance in all marsupials and placentals of the interclavicle
and procoracoid, primitive features shared by the platypus,
pelycosaurs, and therapsids.
One could write that off as homoplasy. But on p. 279 of Romer's
classic _Vertebrate Paleontology_, there is a picture of four shoulder
girdles, and the scapula of the "Virginia opossum" *Didelphis* has a
shape and mid-ridge that is very much like that of all placentals that
I have ever seen, while the one for the platypus is much more similar
to that of the pelycosaur and the therapsid that is in the
reproduction.
That feature, all by itself, cries out for putting marsupials and
placentals in a clade that excludes the platypus, and it would take a
huge number of countervailing characters to overturn that assessment,
unless they happened to be as striking as the shoulder girdle
differences.
"Sharing a more recent
common ancestor"
That might backfire. The way the tree of life is rooted, Morganucodon
might not have a common ancestor with anything except the huge clade
in which Mormota is located, of which the genus Morganucodon is thus
the sister group.
I am unable to interpret that confusing statement. Everything has a
common ancestor with everything else.
Sorry, I should have added "more recent" between "might not have a"
and "common ancestor". It was late and I was getting sleepy.
Still doesn't make sense.
Morganucodon had various common ancestors with everything else [except
maybe prokaryotes] but none of them might have been more recent than
the one it shared with all of Mammalia and most of "Mammaliforma".
Does this still not make sense to you?
No. The part that doesn't make sense is why you brought it up, and why
you think it's a problem of any sort.

At least we've cleared up your initial confusion.

What initial confusion?

As to why it was a
problem initially, I was under the mistaken impression that the
prevailing theory placed monotremes closer to Theria than most if not
all the Jurassic mammals of which we know. That's the way it was in
Carroll's book, and I was afraid my own hypothesis was so radical, it
would face a long uphill battle.

But in fact, it looks now as though my hypothesis is the reigning
orthodoxy.

I don't actually know what the prevailing hypothesis is. But it doesn't matter. Regardless, your statements don't make sense.

[snip side issue which is sure to come up later, on a more appropriate
thread]
If what I said above is true, and Morganucodon had no descendants, the
least inclusive clade containing Morganucodon besides *Morganucodon*
itself, is the huge clade containing Eutheria, and probably
Metatheria.
Better than that. Morganucodon is actually outside Mammalia as commonly
defined these days (i.e. as a crown group). It's a mammaliaform. How is
this a problem?
The concept of "mammaliform" could be a problem if the vexing question
of where monotremes belong takes yet another turn. Because then a lot
of "mammaliform" creatures -- essentially ALL known Jurassic mammals
-- could suddenly become part of Mammalia.
And, judging from what I posted earlier today, this is now the
prevailing hypothesis! The only exception is the Docodonts, about whom
Romer wrote tantalizingly little, and Morganucodon, which some sites
classify as Late Triassic.
Not a problem for me. Is it a problem for you?
No, because I keep carrying old paraphyletic groups around in my head,
and this only requires a minor adjustment for me.
And a very pleasant one, at that. I've always liked the idea that we
have a really diverse batch of living mammals still with us.
Feel free to have a conversation with yourself. But I would appreciate
if you did it in private.

Are you suggesting that anything beyond a one word "No" answer to your
question "Is it a problem for you?" would be a conversation with
myself?

No.

If so, can you give me some pointers as to what genre such questions
of yours belong?
.

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