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Re: (Paleognath monophyly)






From: "David Marjanovic" <david.marjanovic@gmx.at>
Reply-To: david.marjanovic@gmx.at
To: "DML" <dinosaur@usc.edu>
Subject: Re: (Paleognath monophyly)
Date: Sat, 31 Jan 2004 14:37:11 +0100

> a) The presence of such a character state for the dentary would appear to
> indicate that it is a symplesiomorphy in birds,


Quite certainly not, as Mickey has pointed out.

> or a character reversal.

Then let it be a reversal. :-| Firstly, it's still more parsimonious (all
other characters being equal!) to assume that this reversal happened once
rather than several times. Secondly, a reversal can of course be an
apomorphy. Look at your no longer opposable big toes -- an apomorphy of, uh,
humans or so.

See my earlier comments in another reply about parsimony and its relationship to phylogenetic reconstruction.



> It may or may not be a synapomorphy of this paleognathous > assemblage, but its presence in the Confuciusornithidae > seems to make it a contentious character to use.

Not any more than the presence of fused frontals in carcharodontosaurids
makes the use of this character as an apomorphy of anthropoids, and at the
same time of pachypleurosaurs, contentious. The following phylogenetic tree
is aligned in a monospace font:

Pygostylia (misnomer)
  |--Confuciusornithidae
  `--+--?*Jibeinia*
     `--+--?*Longipteryx*
        `--+--?*Protopteryx*
           `--+--?*Eocathayornis*
              `--Ornithothoraces
                   |--the diversity of Enantiornithes (paraphyletic?)
                   `--Euornithes
                        |--*Patagopteryx*
                        `--+--*Yanornis*
                           `--+--?*Yixianornis*
                              `--+--*Apsaravis*
                                 `--Ornithurae sensu strictissimo
                                      |--Hesperornith(iform)es
                                      `--+--*Ichthyornis*
                                         `--Neornithes

> b) The entire suite of characters we see in paleognaths can be explained
in
> terms of neoteny, including that most famous paleognath character, the
> palatal configuration for which the group was named.

Fine -- as I mentioned yesterday, even Cracraft has completely dropped the
palatal configuration. I'd be interested in learning how neoteny can explain
the inflated alaparasphenoid, the highly pneumatic area caudal to the
quadrate articulation, or the strongly forked dentary.



The strongly forked dentary, if it is a character reversal, is readily explicable within a neotenic context, during which see reversal and the expression of primitive characters. Cranial pneumaticity caudal to the quadrate and the inflated alaparasphenoid are the strongest of the characters listed, and the only two which Cracraft & Clarke produced that I would call "unambiguous," however, two such characters do not amount to an overwhelming advantage to the paleognaths-are-holophyletic concept, and at the very least, it that seems that multiple possible phylogenies of Paleognathae are equally viable.




> Paleognathae is entirely polyphyletic, and secondarily derived from within
> Neognathae,


>From _where_ within Neognathae?

As mentioned tinamous seem to be more closely related to the gallinaceous birds than they are to other ratites.



> Some paleognaths may be secondarily derived from neognathous ancestors and
> thus closer to Neognathae than to other paleognaths, again indicating
> polyphyly of Paleognathae.


Again, what would the phylogeny look like? Has one been proposed?


Yes, Houde (1988) which I think Mortimer derided as out of date, presented multiple ppssible phylogenies of the Paleognathae, which Feduccia concurred with in 1996. Under Houde's hypothesis, some paleognaths are more closely related to and independently derived from a grade of basal, paleognathous carinates such as the lithornithids, while others are more closely related to and perhaps secondarily derived from neognaths (e.g., tinamous).


> c) This of course leads one to the timamou/galliform nexus. It is not
based
> solely on the morphology of the sternum, which you seemingly reject
despite
> its being distinct, but also on that of the coracoid. Trivial characters?


Of course not. But they are _fewer_ than the apomorphies of Palaeognathae
plus the apomorphies of Neognathae. :-) All these would have to be explained
as homoplasies in order to make tinamous and galliforms sistergroups, which
means a higher number of ad hoc assumptions than the alternative.



It means a stringent application of parimsony analysis, it does not equate to just-so ad-hoc hypothesis formulation. After all, convergence seems to be rampant in birds.


> d) Or what if that neotenic derivation happened multiple times? Would the
> evidence be found in that some paleognaths are closer to neognaths, while
> others are closer to primitive paleognaths (e.g., Lithornithiformes)?


Yes. Because otherwise we'd never have a reason to think that the neoteny
happened multiple times.

> What morphological data would substantiate this?

Unfortunately, I have to give this question straight back to you.

> The vast disparity in the pelves of the ratites suggests that this
> grouping of paleognaths, at least, is polyphyletic.

No, it doesn't -- evolution happens. Is there reason to think it suggests
more than different locomotory adaptations -- indeed some are cursorial
while others are mediportal --, or perhaps multiple losses of flight (which
are suggested anyway by geography and a few ontogenetic data)?

It is possible, but what uniquely derived characters are present in the pelves to unite ratites? To my knowledge there are none. Given this, why should we presume that the osteology of the pelvic girdle in these forms is a function of common ancestry, and not reflective of polyphyletic derivation of these birds?




> Then there is the tremendous diversity in the > structure of the paleognathous palate itself, which > alone seems difficult to reconcile with the idea than in its > derivation we are witnessing one example of neoteny > in a holophyletic lineage,

Just how tremendous is it? How tremendous does it have to be that you think
it couldn't have evolved from the structure of an exclusive common ancestor?



The differences are sufficient to delineate four palatal configurations within the paleognathous palate, which McDowell did in the late 1940s (48, IIRC), and possibly five if one considers the Malagasay aepyornithids.


> and so on and so forth.

:-) I'm interested in the whole list. If you have time, I'd like to ask you
for it.


I have already outlined the principal case for the neotenic and polyphyletic status of Paleognathae, and ratites. If you desire further enumeration, I would suggest checking the far more detailed sources from which I have derived this standpoint (e.g., Houde 1988, Feduccia 1996, etc.)


> e) Ligon's work demonstrates that male parental care is the principal, but
> not exclusive condition in ratites. Perhaps it represents an autapomorphy
> of the ratite assemblage, with little if any bearing on the unity of
> Paleognathae?


What is its distribution in Tinamidae, and what does the phylogeny of that
group look like? (Not a rhetorical question -- I have no idea.)


Tinamiformes is monotypic, with Tinamidae composed of nine genera and 47 species. I am not aware of any extensive cladistic analysis of the Tinamidae, but it would appear that _Tinamus_ is the most basal member of the family. IIRC, incubation is carried out by the male in Tinamidae, with nest-building and parental care subsequent to hatching, shared.


> f) Last I knew, the ergilornithids had not been advanced as the ancestors
of
> _Struthio_ since 1985, with the general consensus since then being that
> Ergilornithidae represents a textbook case of convergence, in this case
with
> ostriches.


Good. But if ostriches are not paleognaths, and if ergilornithids aren't
their closest relatives either, then what is?


Ostriches are paleognaths and are perhaps derived from within the lithornithithid grade. The closest link between these two taxa is _Palaeotis weigelti_, but the first _Struthio_ fossils do not appear until the Miocene.


JGK

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