[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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: Fri, 30 Jan 2004 19:32:15 +0100

> At any rate, the characters advanced by Cracraft
> & Clarke (2001) are as dubious as any others advanced in defense of
> paleognath holophyly.  The posteriorly forked dentary is apparently
> present in Confuciusornithidae,

So what? Fusion of the frontals is a good synapomorphy of Anthropoidea,
despite also occurring in Carcharodontosauridae and Pachypleurosauria.
Besides, Cracraft & Clarke write "strongly forked". They don't seem
to quantify this (which is a bad point for them).

> and the remaining traits are all as explicable
> within the framework of neoteny


> Furthermore, varying patterns of pneumaticity in
> the cranial elements have been recorded from throughout Archosauria.

:-) That's precisely the point.

> The fact that that parental care is not exclusively restricted, at least
to my
> knowledge, to males in paleognaths renders this is a weak synapomorphy,
> as does its lack of applicability to extinct paleognaths, such as the
> lithornithids.

Its lack of applicability to, say, *Ichthyornis* does make it somewhat
weaker. But nevertheless, crocodiles and neognaths lack this character, so
it is most parsimoniously optimized as an unambiguous apomorphy of
Palaeognathae (in cladospeak).

> What remains is scant evidence to contradict a significant
> amount of work indicating that the paleognaths are polyphyletic,

What do those hypotheses look like? Even Feduccia doesn't agree with
ostriches being derived from ergilornithid cranes, and I haven't seen any
other explicit hypotheses of paleognath polyphyly.

Sorry for my too short explanation of why ABSRD is meanwhile considered
pseudoscience (in my last post). An important part is that Feduccia et al.
offer no alternative. They never make clear what, if anything, they think is
the closest known relative of birds -- which would give us a testable
hypothesis. They just say ABSRD -- "anything but a small running dinosaur".

> not the least of which is the neotenic derivation
> of the paleognathous palate itself.

What if this neotenic derivation happened only once? Then it would still be
a synapomorphy of Palaeognathae. :-)

> Consider also that various members of Paleognathae, e.g.,
> Tinamiformes, 'may" (I emphasize may because of the similarities between
> Lithornithiformes and Tinamiformes which so impressed Houde) be more
> related to Neognathae (in the tinamou's case, to Galliformes) than they
> to other paleognaths.

Feduccia points out (in his 1996 book) the similarities in sternal shape of
Tinamidae and Galliformes. That's a rather small number of characters,
however -- and not applicable to ratites with their reduced sterna. So
perhaps we're looking at synapomorphies of Neornithes here.

> From what I can make of the situation, the case for a
> holophyletic Paleognathae is extremely tenuous.

If it's less bad than all alternatives, then I'll stick to it, however.

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

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. To me this is the most important of points because if the morphology of the paleognaths can be derived via neoteny, at the very least it renders alternative hypotheses whereby:

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

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

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? No more than those invoked by Cracraft & Clarke in defense of their alternative hypothesis.

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)? What morphological data would substantiate this? The argument for a relationship between the Tinamiformes and Galliformes I already mentioned, but there is more. The vast disparity in the pelves of the ratites suggests that this grouping of paleognaths, at least, is polyphyletic. 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, and so on and so forth.

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?

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.


Check out the coupons and bargains on MSN Offers! http://shopping.msn.com/softcontent/softcontent.aspx?scmId=1418