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Re: Phylogeny and Distance



Jaime and Tom,
The most primitive neognaths and the most primitive paleognaths are admittedly virtually equally related to any other group, including Archaeopteryx, Velociraptor, or even Homo sapiens.
But from that point, the differences in evolutionary rates (generally greater amongst neognaths) results in a growing differential of relatedness as time progresses.
Compared to the common ancestor of paleognaths and neognaths, a crow, hummingbird, or other present-day neognath will have fewer genetic similarities with such a form than will a tinmou or even a ratite. Even Darwin recognized this and based his taxonomic philosophy upon it.
****What is not being recognized here is that "relationship" is not the same thing as "relatedness", and therefore neither are the degrees of relationship and relatedness. Siblings may share a common relationship, but the number of genes they share in common can vary from 100% (in identitical twins) to extremely low percentages in rare instances (the disparity in relatedness can be enormous even among the closest of relatives).
------Ken Kinman
**********************************************************
From: "Jaime A. Headden" <qilongia@yahoo.com>
To: dinosaur@usc.edu
CC: kinman@hotmail.com, dinogeorge@aol.com
Subject: Phylogeny and Distance
Date: Tue, 9 Jan 2001 18:38:19 -0800 (PST)

Ken Kinman <kinman@hotmail.com> wrote:

<I am certainly no devotee to the "science" of the Tonight Show
or any other mass media outlet. But on the other hand, there is
more to "relatedness" than just strict phyletic relatedness, and
I'm a little shocked that you would say evolutionary rates are
irrelevant. I think that they are very relevant...>

  Phylogeny on its face is the arrangement of organisms in an
assumption of relationship. To quote from my Webster's Student
[okay, it's not the Oxford, I don't actually _own_ one of those
monsters!]:

  _relation_ = "... 6. [pl.] the connections between or among
persons, nations, etc."

  It is in this sense that relationship is utilized. It implies
the connections, not the distance, between something. Becuase
this is implicit in making a phylogenetic statement, I don't
think this is nitpicking either.

  Phyletic distant in an assumption of relationship is
irrelevent, pertinent in the sense of time when inferring
relationship. The number of modifications an organism goes
through is its own business and doesn't overturn the statement
or assumption that this organism is any more closer to an animal
that lacks these modifications than to another. This said,
paleognaths and neognaths have the same amount of basic shared
differences in their ontogeny at least that demonstrate neighter
is closer to the base of Aves than the other. Some morphological
studies and a few less molecular studies have supported the
paraphyly of Paleognathae throughout Neognathae. This requires
examinations. Neornithes and Ichthyornithiformes [Carinatae]
have the same shared basic morphology and thus neighter is
closer to the base of Aves than the other. And so on down the
tree.

  Neotenic modification can be shared by unrelated organisms,
requiring rigorous second glances ... and third, and fourth....
For example [e.g.], *Bagaraatan* and *Allosaurus* share a
neomorph bone, the antarticular [on the medial and dorsal side
of the articular bone, near the surangular and prearticular,
medial to the articular socket], but this appears not to
correspond with phylogeny. The bone may persist as cartilage in
intermediate forms, but there's no real way to test this.
*Bagaraatan* and *Allosaurus* are distant from each other in a
phyletic sense: analyses published, or not, as in Mickey
Mortimer's statements online, have suggested this form is a
coelurosaur at least, and possibly maniraptoriform to
maniraptoran. Big distance from carnosaurs like *Allosaurus*.
Unresolved placement ... gotta love those critters you couldn't
shoehorn if you were Atlas.

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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