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Dinogeorge Digest #12



Subj:   Re: THERIZINOSAURS AND LOGIC
Date:   98-07-29 03:54:18 EDT
From:   Dinogeorge
To:     m_troutman@hotmail.com, znc14@TTACS.TTU.EDU
CC:     qilongia@yahoo.com, Tetanurae

In a message dated 98-07-29 03:08:57 EDT, m_troutman@hotmail.com writes:

<< Reversals happen in evolution frequently. >>

You have no basis for saying this at all, since there is really no way to
confirm that any cladogram is true. How many cladograms have you enumerated
the number of reversals in? What is "frequently"? What, for that matter,
qualifies as a "reversal"? A derived state that resembles a primitive state?
Or the genuine reappearance of the primitive state? And how would you tell?

And--convergence happens "even more frequently" (whatever that means),
particularly with bistate characters. Take convergence over reversal every
time as a parsimonious working hypothesis. Or a brand-new lineage.

Reversal should be considered a last resort, an extraordinary claim justified
by extraordinary proof, not business as usual.

I agree reversals can occur, but not nearly as readily as everyone seems to
think they do. It's more likely faulty cladistics than reversals in most
cases. (These statements refer to morphological characters, not protein
sequences, in which reversals can be expected to occur every so often simply
by chance.)

Subj:   Re: THERIZINOSAURS AND LOGIC
Date:   98-07-29 02:09:14 EDT
From:   Dinogeorge
To:     m_troutman@hotmail.com, znc14@TTACS.TTU.EDU
CC:     qilongia@yahoo.com, Tetanurae

In a message dated 98-07-28 23:18:04 EDT, m_troutman@hotmail.com writes:

<< Along with the expanded and inflated parabasiphenoid, >>

As I have repeated here until blue in the face: bullatosaurs have an inflated
parasphenoid, _Erlikosaurus_ has a pneumaticized basisphenoid. These are
completely different skull bones that, in _Erlikosaurus_, have a fused suture
where they join at the bottom of the braincase. This is NOT a character
shared by bullatosaurs and segnosaurs. Read Clark et al.'s paper on the skull
of _Erlikosaurus_, where this anatomical blunder is perpetrated. (Why wasn't
it caught in review??) And you wonder why I'm beginning to question the
sanity of this discussion?

I, too, once believed that segnosaurs were theropods, until I actually saw
the type specimen of _Alxasaurus_ on display in Toronto in December 1993. I
noticed that the bones simply didn't match the "casts" that were mounted, in
a very theropod-like skeleton, alongside the display (I don't think they were
actual casts; they seemed more like bones modeled to look something like the
bones of the type specimen). Plain and simple: somebody goofed. So I
scrutinized the Russell & Dong paper (and other segnosaur papers) very
carefully, eventually drawing two conclusions: (1) _Alxasaurus_ is very
likely a primitive segnosaur, and (2) segnosaurs aren't theropods; they have
simply accumulated a number of theropod-like features during their long,
cryptic, and independent evolution from sauropodomorphs or very basal
ornithischians.

The questions to be answered are how and why did this convergence come about?

Because if this isn't convergence, and segnosaurs are indeed maniraptorans,
then maniraptorans must have evolved before the beginning of the Jurassic
(that's what the jaw in the July 16 _Nature_ says), and dinosaurian
diversification, from sauropods to avialan birds, would have been essentially
finished by the beginning of the Jurassic. Thus there could have been flying,
archaeopterygiform dinobirds >well< before the beginning of the Middle
Jurassic. BCF might well walk in through a back door that I hadn't previously
considered.

Sorta puts Sankar's _Protoavis_ and _Shuvosaurus_ in a different light, eh?

Subj:   Re: OCCAM'S RAZOR & THERIZINOSAURS
Date:   98-07-28 17:38:28 EDT
From:   Dinogeorge
To:     darren.naish@port.ac.uk
CC:     Tetanurae, mlb194@soton.ac.uk

In a message dated 98-07-28 16:35:58 EDT, darren.naish@port.ac.uk writes:

<< Plus the fact that every theropod worker*, without 
 exception so far as I know, finds Therizinosauroidea nested somewhere 
 within Theropoda.  >>

Then one of these days, they're in for a big surprise.

<<However, I honestly would not have expected the presence of a 
therizinosaur in the Lower Jurassic. Does everyone advocating a 
bullatosaurian or oviraptorosaurian affinity of therizinosaurs really 
appreciate what this means? 

(Or, is Chatterjee right??)>>

Oddly, _Shuvosaurus_ is not even mentioned in the _Nature_ paper, even if
only to be dismissed. So the paper doesn't quite present a complete picture
of citations of putative early coelurians.

<<Having said that, I do not disagree with Pete as to the idiosyncratic use
of Coeluria.  >>

It's only "idiosyncratic" until you get used to using it. Coeluria Marsh is a
dead-on synonym for Coelurosauria Huene, is easier to spell and pronounce,
and has nomenclatural priority (if you consider that to be important). There
was no reason at all for Huene to have proposed the later name instead of
using Marsh's, still less for it to have become predominant.

Maybe I should start calling theropods "Goniopoda" and sauropods
"Opisthocoelia" or even "Cetiosauria." These names all have priority over
Marsh's better-known terms and have been "forgotten" for no good reason, just
because of some kind of "idiosyncratic" popular scientific fashion.

Subj:   Re: Caudipteryx and BCF
Date:   98-07-28 17:38:16 EDT
From:   Dinogeorge
To:     granth@cyberus.ca

In a message dated 98-07-28 16:35:41 EDT, granth@cyberus.ca writes:

<< Where does Caudipteryx fit on the BCF dinosaur family tree? It looks
almost Oviraptorish. >>

It looks pretty good right where the describers in the _Nature_ paper placed
it.

Subj:   Re: ORNITHOMIMID THERIZINOSAURS
Date:   98-07-27 14:46:51 EDT
From:   Dinogeorge
To:     znc14@TTACS.TTU.EDU, m_troutman@hotmail.com
CC:     qilongia@yahoo.com, dinosaur@usc.edu, Tetanurae

In a message dated 98-07-27 13:11:36 EDT, znc14@TTACS.TTU.EDU writes:

<< As a quick aside, basal maniraptorform phylogeny is in such flux
 that it is probably best represented by a trichotomy of Maniraptora,
 Ornithomimisauria, Troodontidae, Tyrannosauridae, Therizinosauroidea, and
 Oviraptorsauria (did I forget anybody?). Mix and match to your heart's
 content, and wait for the next Holtz monograph... hopefully it'll be out
 before the next Star Wars movie (nice safe time fram for you there...). >>

The new Lower Jurassic Lufeng segnosaur jaw, only a few inches long,
described in the current _Nature_ (July 16) as a therizinosauroid jaw, (1)
looks very segnosaurian; (2) looks somewhat prosauropodan or even
ornithischian; and (3) does >not< look at all coelurian: ornithomimid,
oviraptorid, troodontid, dromaeosaurid, tyrannosaurid, maniraptoran, or even
theropodan. Unless you think that basal coelurians should have lateral
shelves on their dentaries and lateral ridges on their coarsely serrated,
leaf-shaped teeth, that is.

Subj:   Re: THERIZINOSAUROIDEA
Date:   98-07-27 12:32:44 EDT
From:   Dinogeorge
To:     Tetanurae, qilongia@yahoo.com, dinosaur@usc.edu
To:     James.Close@LibertyMutual.com
To:     tlford@ix.netcom.com, m_troutman@hotmail.com

In a message dated 98-07-27 00:06:45 EDT, Tetanurae writes:

<< To date, no cladistic analysis has shown that therizinosaurs do NOT fall
within Theropoda. >>

This, of course, is no reason to assume that segnosaurs are
theropods--particularly the nearly insane notion that segnosaurs are
bullatosaurs related to ornithomimids(!). What next? Frogs that are the
sister group of cats? I have a paper in preparation that, as far as I'm
concerned, will finally demolish this absurd notion. (It surely won't, but I
can't help that.)

Subj:   Re: species
Date:   98-07-24 23:07:50 EDT
From:   Dinogeorge
To:     znc14@TTACS.TTU.EDU
To:     Steve.Tomporowski@us.ms.philips.com
CC:     cbrochu@fmppr.fmnh.org, dinosaur@usc.edu

In a message dated 98-07-24 16:10:42 EDT, znc14@TTACS.TTU.EDU writes:

<< Look at the *biological* species concept: "a group of continuously
 interbreeding populations" (paraphrased). This concept seems to be applied,
 or at least concieved of, outside of an historical context. When we place it
 in an historical context, what happens? When one or more populations becomes
 reproductively isolated from the group, is the original species changed?
         The answer is a resounding "YES". >>

So is there just one species of barn owl, or are there fifty? If you say that
new species arise whenever the population mix changes, that way lies madness.
I can't think of a more impractical definition of a species.