Re: BIRDY _ARCHAEOPTERYX_

["Matthew Troutman" <m_troutman@hotmail.com>]

>As I mentioned some months ago, there are indirect results in the 
>skull arising from flying/non-flying differences.  Of course, 
everything >in a flier's body is subject to extreme weight saving 
pressure, and this >is a main cause of changes (in addition to wing 
mechanics), but it is >also likely that sheer size would lead to 
different optimal structures. >Also Archae probably ate invertebrates, 
or possibly flimsy pterosaurs >whereas some later flightless mani's ate 
beefier stuff.  Some things >are just to complex for us to make sensible 
guesses at, and a lot to >do with the palaeontology of birds skulls 
falls into this category.

Read Witmer and Rose (1991; Paleobiology).  They discuss the jaw 
mechanics of _Diatryma_ and predatory birds.  Basically, big birds with 
large jaw muscles did not revert to their ancestral condition in the way 
that you advocate for birdy K theropods; they made do with what they 
had.  Look, stuff like triradiate palatines in small ancestral birds are 
very unlikely to have reverted to the ancestral condition.  Alvarezsaurs 
kept their triradiate palatines and prokinetic skulls, as well as the 
lack of the coronoid.  If macropredation was a big factor in the 
modelling of the dromaeosaur, oviraptorid, troodontid, ornithomimid, 
therezinosaurid, and tyrannosaurid (I sincerely doubt macropredation in 
oviraptorids, troodontids, ornithomimids, therezinosaurs and possibly 
small dromaeosaurs or dromaeosaur-like creatures) skulls then it may not 
be advantageous to revert to the ancestral condition (which may not be 
advantageous to predation in the first place!).  It may be more 
advantageous to evolve large thick sympheses, large mandibular muscles, 
and larger overall skulls and beaks (read Witmer and Rose).  

Of course, the discovery of new fossils will ultimately prove or 
disprove these ideas.  

>So changing physical size by an order of magnitude or two has no 
>effect? What about the *results* of being able to fly?  How can E & >W 
be sure that some of these skull changes are not required to >protect a 
flightless animal from falling on its nose from a height of five >feet 
for example?  It is generally accepted that weight is an important 
>factor in bird skull design - it's the reason given for their change 
from >teeth to beaks.  Presumably they also decreased the force of their 
>bite.  Presumably this would be reflected in skull structure.  It is 
>difficult to say anything for certain about palaeontology, but much 
>easier to be certain about palaeontologists; the above statement by >E 
& W is wrong.  Incidentally, are they saying that the difference is >so 
great that evolution between birds and "proper dinos" in either 
>direction is impossibe?  Also, I would be intrested to see what skull 
>similarities are shared between Archae and 
>_Protarchaeopteryx_/_Caudipteryx_.

_Caudipteryx_ and Protarchaeopteryx_ show many skull details that are 
distinctly theropod-like and are not found in _Archaeopteryx_.  I don't 
have the paper on hand so bear with me; I think that _C._ has a 
tetraradiate palatin and a coronoid.  Overall, they are not as much 
_Archaeopteryx_-like as they are theropod-like.  I seriously doubt that 
they are secondarily flightless, but even if they are they are too 
specialized to be ancestral to the birdlike K theropods.  

Without _C._ and _P._ the logic still holds up.  Basically, all 
flightless  birds that I know of show the same basic bird structure to 
ther skulls.  Even phorusrhacids do not show all the features that K 
theropods show; their skulls are extensively remodelled, but they do not 
resemble the ancestral theropod condition.  Plus, it is not for certain 
that _Archaeopteryx_ ate "flimsy" foodstuffs Thulborn and Hamley say 
that insectivorous mammals show large amounts of cusps on tightly packed 
teeth.  _Archaeopteryx_ does not show these features.  Another 
consideration is again, how advantageous is the ancestral condition?  
Without detailed biomechanics you cannot prove much of anything.  Even 
if it was more advantageous, you cannot justify your logic that it would 
be easier for early birds to revert to that condition when they could 
follow the basic bird trend of enlarging bone size, girth, strength, and 
muscle force.  

I am saying that the K theropods represent excellent archetypes for the 
structure of early birds.  Early birds, however, are too specialized 
towards the bird condition to be ancestors of some of the K theropods.  

You also seem to be saying that the K theropods are adapted solely 
towards predation; I cannot see this except in tyrannosaurids.  
Dromaeosaurs and troodontids, except in the larger dromaeosaur forms, 
are not really of the good macropredator construction in my mind: too 
small in a world of giants.

Anyway, another fault of your flight/skull argument is that it is purely 
hypothetical.  We have no ideas about the exact habits of these extinct 
creatures.  Without detailed biomechanics, a good fossil record, and a 
well-constructed and supported phylogeny your arguments suffer.  

>>But it is too birdlike to be the ancestors of K theropods!  Tell me, 
do
>>you think that the characters above are related to flight?

>(See above.)

See above.  

>Padian also said Archae did not display any particularly arboreal
>adaptations.  He also said that the mechanically totally unsuited
>maniraptoran hand was designed to give "killer blows" (rather than >for 
hooking and pulling).  I think I'll take his opinion on an animal for 
>which he has only the teeth with a pinch of salt.

Not teeth.  If I remember correctly limbs and a pelvic girdle.  

>I don't think it requires too great a leap of the imagination to see it
>leading to _Protoarch/Caudipteryx_, and thence Ovi's, nor to >something 
like _Rahonavis_ -> _Veloci_, do you?  Oh - perhaps you >mean a 
progenitor of *all* theropods.  Well, time would rule out >Archae, 
certainly.  The thing is, there are "theropods" and >"theropods", aren't 
there?!

_Velociraptor_ => _Protarchaeopteryx_/_Caudipteryx_ => _Archaeopteryx_ 
=>/+ _Rahonavis_ fits the anatomical evidence better.  

>I'm not sure this helps your argument more than it does mine!

Exactly!  Then we must go to the anatomical evidence.

>Loss of bite force particularly at the front of the snout due to weight
>loss, eating smaller prey, both, or possibly other things too.

Falconiforms and owls do not have a loss of bite force and they fly 
perfectly well.  

POSSIBLE MESETHEMOID:
>General change in skull structure (see above).

If it is present, why lose it?  It simply takes over the place of the 
ascending ramus of the maxilla which is present in dromaeosaurs and all 
the birdlike theropods.

>How many insectivores are known with serrated teeth?  Only 
>flesh-rippers need them (and not all of them: mammals slice, crocs 
>swallow whole or use their short necks to twist or just "flip" the prey 
>in two. [Cor did you see that program the other day where the croc >had 
a pig in its mouth and just flicked its head and the back half of >the 
pig just vanished in the space of a couple of frames?!!  But I 
>digress]).

See above for insectivore arguement (it doesn't hold up.)

>>4)  ?Loss of contact between jugal and postorbital and squamosal >>and 
quadratojugal (Elazanowski and Wellnhofer state the elements >>may be 
too short to reach each other).
>>5)  Postorbital process.
>>6)  Small squamosal.
>>7)  Non-verticalized braincase.
>>8)  Derived paraoccipital process.

>General lightening of skull/other changes (see above).

I would hardly call the characters 5, 7, and 8 characters related to 
lightening of the skull.  They also do not change the shape of the much 
either.  

>>9)  No sagittal crest.

>If it was for display purposes it would have been quite labile; loss of
>weight benefit would have impelled the change.  If it was for muscle
>anchoring, decreasing jaw muscles would have been adequate >reason for 
losing the crest, and for regaining it.

Why do ornithomimids and therezinosaurs need large M. pterygoideus 
muscles?  

>A strong sternum is pretty useful for flying, don't you think?  Another 
>less obvious point is that the thorax front in a non-flying theropod 
>must be able to sustain hard impacts without permanent damage so >they 
have rubbery cartilagenous components in those bones.  It may >well be 
that their furculae didn't ossify until they reached an age >where they 
didn't fall over so much.

Why then do flightless birds usually keep a single sternum?

<<We get a better understanding of phylogeny if we think carefully about 
morphology, and don't ignore time.>>

I find it most unlikely that losing multiple characters and then 
regaining it is something that can happen.  

Of course, lets not forget the maniraptoriform genera _Coelurus_ and 
_Ornitholestes_.  

Regards,

Matt Troutman

______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com