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Re: Arctometatarsalia



On Tue, 26 Feb 2002, Jaime A. Headden wrote:

>   -- is usable for pterosaurs as well. As the definition requires that the
> condition of *Vultur* possess this, including taxa with which the
> condition is homologous (synapomorphic) with that of _Aves_, this then
> includes the condition in any other possible taxa which have such a
> feature.

No, it only includes taxa for which the character is hypothesized to be
synapomorphic with that character in _Aves_ (or at least _Vultur
gryphus_). A keeled sternum is NOT a synapomorphy of _Ornithodira_. It's a
synapomorphy of _Pterosauria_ and of some clade within _Avialae_ (and
perhaps of some clade within _Alvarezsauria_ as well).

> Because in the operating definition, the inclusive taxa are
> limited to Panavians (= homodefinitional junior synonym of Ornithosuchia).
> In such a relationship that Ornithodira is contained within Archosauria,
> rather than inclusive of Archosauria, and pterosaurs are closer to birds
> than are crocodiles, then it becomes problematic to yet another degree,
> and Carinatae in this sense becomes a _senior_ synonym for Ornithodira,
> Ornithosuchia, _and_ Panaves.

???

> only homology (which is not synonymous with "synapomorphy"; only
> condition of form and use)

The authors consider these terms synonymous. Maybe not a great idea, but
that's how they present it (by writing "synapomorphic" in parentheses
after "homologous").

>   Any clade . . . except apomorphy-based definitions, which are based on
> the condition of a feature in _one_ taxon and their first prescence and
> all descendants of the first organism to demonstrate _that one feature_.

correction: all descendants of the first *ancestor of said specifier* to
demonstrate that one feature.

> <I think maybe you're using the word "homologous" differently than they
> do. They are using it to mean "synapomorphic".>
>
>   Exactly. The word is, as I understand it, in meaning "matching in
> structure or position, form, etc." This is how my Webster's (Macmillan
> Press, 1995) defines it, in any course.

>From Merriam Webster's on-line:
homology:
1 : a similarity often attributable to common origin

They just got rid of the "often". It is very clear in the text that they
mean "synapomorphic" when they say "homologous", such as when they
explicitly addressed the pterosaur issue.

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