[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Fw: More on Argentavis
Again forwarded with permission, again comments interspersed.
----- Original Message -----
From: "evelyn sobielski" <firstname.lastname@example.org>
Sent: Saturday, July 07, 2007 10:04 AM
This, of course, would still need to come with a
blanket disclaimer. The Morrison Fm [...]
Most of the time it was worked indiscriminately. I
mean, when was "continental drift" being universally
accepted? It was still considered a "hypothesis" by
many 40 years ago. The availability of GIS data has
likewise exploded in recent decades.
I don't understand what you mean.
(I have read some of the last fixist books from the 1960s, though. Quite
funny in hindsight, and probably somewhat desperate to a contemporary
In Quaternary avian paleontology (in which it is of
course much easier) sites are rarely chanced upon
anymore, but intentionally targetted and tested.
Quaternary paleontology is for losers... :->
> _Limenavis_ for example is useful as an outgroup
> that's very close to the interesting bits.
If only it weren't just a fragmentary wing...
...of someting quite close to and older tham a ratite
ancestor which has reasonable chances to have been a)
flying and b) still a common ancestor of all ratites.
A partial wing's not that bad.
Despite consisting of a few crumbs, it preserves autapomorphies, so it's not
likely to be part of the lineage of ratite ancestors.
The other way around: you know that you need to
_add_ characters and/or taxa.
Always, but it's a tradeoff. It's not easy and often
impossible to *know* the strength of a character's
signal, but there is technically no reason that
forbids a character to violate parsimony again and
again. Cladistic analyses make assumptions about the
evolutionary behavior of characters, to which
characters are not obliged to adhere. If in doubt,
refine. Removing is indeed problematic.
Cladistics is not the assumption of the minimization of convergence. It is
the minimization of the assumption of convergence.
Sure, as with molecules, not all morphological characters evolve at the same
speed. That is why more characters are better: the signal will add up, and
the noise will cancel itself out.
The phylogenetic signal of a character can be tested. Download Mesquite
http://mesquiteproject.org, make a character matrix with the taxa and the
character of interest, draw a plausible tree with those taxa (that could be
the prevailing literature opinion, or all of them, as long as the character
of interest was not used to build that tree), have Mesquite simulate
another, say, 9999 random trees, and it will tell you how often the random
trees have a more parsimonious distribution of the states of the character
of interest. In my M. Sc. thesis dinosaur size is more parsimoniously
distributed in the tree I used than in all 9999 random trees; that means
(unless the tree I used is _far_ off) that the probability that size does
not carry a phylogenetic signal is at most 0.01 %.
> Might even help pinpointing promising strata.
The limiting factor on new discoveries is not the
availability of strata,
it's the number of paleontologists in the world...
True, but that does not mean the resultant geodata has
to be thrown away.
I don't know what you mean.
> I have checked on the molecular studies since the
> data started to become good (ancient DNA, decent-
> length sequences) and *something* is odd about it.
> Can't lay my finger on it... might be a bad signal-noise
> ratio, might be an apomorphically altered metabolism
> adding noise, or whatever. Still, the moa sequence
> divergence, which should be comparable with with
> crown taxa, is odd. Morph/mol evolution rates don't
> seem to match up. Massive genetic drift, with Taupo
> volcano blowing up ever so often again? I don't know...
I don't understand. Please explain.
If I could understand what's going on, I wouldn't be
having a problem ;-)
Well, what do you mean by "Morph/mol evolution rates don't seem to match
up", and why are you surprised if they don't (*Latimeria* has quite a long
branch molecularly, much less so morphologically)?
OK, so if you have read the recent studies on
phylogenetics of crown Aves down to alpha level and
e.g. Steadman's latest book, or any other modern study
of avian biogeography, you'll notice this:
inconsistencies are usually due to any of very few,
very common reasons. There are avian case studies
available now for almost any conceivable problem in
phylogenetic reconstruction, based on a variety of
With the proposed ratite trees, it's obvious they
don't agree, but no single most parsimonious synthesis
of phylogeny and evolutionary scenario has been
proposed or is suspected. As of 2007, this has become
quite rare in crown Aves, especially in a lineage-rich
In computers slang: it can't be hacked; at present,
we'd have to brute-force it.
Livezey & Zusi 2007 is brute force! :-)
I don't think that's what you mean. It shows no
details smaller than the
existence of the Juan de Fuca plate.
Best Web image I found. Look at the notch near NC
(Fiji is just barely visible at its rim). Brief
discussion what happened and happens there:
That page has a lot of interesting text.