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Re: Protoavis



Good Morning...


-----Original Message-----
From: Jaime A. Headden <qilongia@yahoo.com>
To: dinosaur@usc.edu <dinosaur@usc.edu>
Cc: larryf@capital.net <larryf@capital.net>
Date: Tuesday, March 02, 1999 2:35 AM
Subject: Re: Protoavis


>  Sorry about the name mix-up.

No prob!

>
>Larry Febo wrote:
>
><Pterosaurs did have (what is termed by Padian at least) an
>acrocoracoid process. They may have lacked the furcula as part of the
>structure, but it`s there nonetheless, and functions pretty much
>exactly as it does for a bird.>
>
>  An acrocoracoid process, pulling the _M. biceps_ muscle (being
>redundant for simplicity) would fling the humerus sideways---it does
>in us (the muscle, that is) and in large terrestrial reptiles (crocs
>and monitors) you see the huge sideways lunge of the body with a
>sideways fling of the arm on the opposite side of the lunging
>direction. This is supported by the acrocoracoid, and suggests that
>the structure would have developed---originally---for just such a
>purpose to a extreme method in particular groups.

_M.biceps_muscle (is that another term for "supracoracoideus muscle"?). I
havn`t studied the musculature all that close ..yet, but rely on what I`ve
read in Carroll`s "Vertebrate Paleontology and Evolution", where he states
(pg342)..."The configuration of the coracoid in Archaeopteryx indicates that
the supracoracoideus muscle retained the primitive function, common to other
tetrapods, and would have served to pull the humerus anteriorly and
ventrally."

 When the
>ornithodiran line became bipedal, starting somewhere around
>*Lagerpeton* or so (with long forearms but with big feet) the
>acrocoracoid was preempted.

I think that all these features were flight related. I`ve been thinking more
and more about the "Advanced Mesotarsal" ankle and I think that this (which
limits motion to a simple hinge, not allowing a "twisting" of the foot),
along with fused metatarsals, and elongation of the metatarsals, are all an
adaptation for "leaping". I think this ankle developed in conjunction with
the advanced shoulder girdle, acrocoracoid process, and flapping flight. A
bird, or pterosaur would have to leap free of the branch it was perched on
to not damage its wings when it takes flight.

Now, if pterosaurs were related closely to
>dinosaurs (= Ornithodira) there would have been a common, terrestrial
>origin (and possible bipedal one) for both lineages (provable, I
>guess, if *Scleromochlus* was a pterosaur ansestor) then development
>of the acrocoracoid into a flight structure among birds and pterosaurs
>in convergent. I don't argue for this, or for yours, Larry. I actually
>like the elegance of your theory.


("like the elegance"...well thanks!)  I hope it also resolves more issues
than it brings up!
See, I can`t support a cursorial origin for flight in pterosaurs (as Padian
proposes), pretty much for the same reasons as for bird flight. I just thing
the presence of a prior gliding stage makes much more sense "physically". (I
like Bock`s arguement).Scleromochlus and Lagosuchus, I see as being
Pterosaur, (or near pterosaur descendants, not ancestors. (Possibly even
descendants of the bird side of the pterosaur-bird split which I think
occurred very soon after pterosaurs achieved full powered flight).


>
>  However, the lagosuchid -> herrerasaurid -> dinosaurian ->
>theropodan -> maniraptoran -> bird relationship argues against such
>association. Alternatively, a common ansector for pterosaurs and birds
>as full flight development so early on leaves most of these dino-birds
>in the dust.

I think the common ancestor was a prolacertiform. Eoraptor, Herrerosaurus,
Lagosuchid on up were secondarily cursorial forms that inherited these
"avian" features at different stages, and therefor may "appear" to actually
be evolving  along a path towards the advanced maniraptoran condition, but
they are only "mirroring" what is occurring in the arboreal habitat.

 Were dinosaurs trying to redevelop birds? These animals
>were getting bigger, not smaller, or more terrestrial. Looks like
>they'd taken a hop _down_, not trying to claw their way back _up_.
>BCF, if I'm not mistaken, but George and others have argues this all
>before.

Yes!...They ALL hopped down.

>
>  The point I'm trying to make is that is birds _had_ developed early
>on, one would think that all theropods wouldn't retain, loose, and
>regain all these "bird" characters. Rather than having a common origin
>for all flight features that, orignally, had nothing to with flight.
>Arboreality? Scansoriality? You be the judge.


Some may have begun to loose the avian features, by becoming more and more
adapted to their terrestrial  enviornment.


>
>  And about Protoavis: the hand possesses all fight metacarpals, with
>several having the appearance of being warped and distorted. And there
>is a photo of the specimens in a relatively accessible resource:
>Feduccia's _Origin and Evolution of Birds_. It's an itty-bitty
>picture, but there _is_ one.

Yeah,...I photocopied a lot from that book,...the picts look
iss-poor.( Guess I`ll have to but the book!)

>
><As far as bats flying as "good" as birds,...it`s pretty subjective,
>but I don`t think they`re as good long range, and I`m assuming that
>hummingbirds might be able to outmaneuver them...(though not at
>night!).>
>
>  Bats do fly for long periods, hours on end, and eat on the wing,
>being fully capable of "netting" prey by the wings and eating while
>flying. For hours on end. The size of hummingbirds gives them much of
>their maneuverability, having so little mass to have to resist (hence
>the teeny wings) that the point is pretty moot, IMO.


When you talk about birds and pterosaurs, ...people always bring up Bats! I
hate to group the three. Birds and Pterosaurs are OBVIOUSLY much closer than
either is to bats.......(that`s how I feel about it). Comparisons can only
be made on vaguely similar
physical mechanics, I`d just as soon leave them out of the equation
alltogether!

>
><Archie flew , I think,..(although some say not very
>efficiently),...it did not have an acrocoracoid process,...did have a
>biceps tubercle though.>
>
>  Demonstrating, in the least, that the ac. pr. is a flight related
>feature, not a flight requisite one, but bats should also point that
>out.


OK. They`ve even found this out by cutting the Supracoracoideus tendon.
Birds could still fly, but couldnt initiate the flapping motion necessary
for takeoff. I don`t think I said it was necessary for flight, but that its
presence was an indication of ADVANCED flight capabilities (what else would
it be for?).
>
>==
>- Often, it is the man who is brought
>  down the path to the end who does
>  not see his own steps. -

>
>Jaime A. Headden
>
>Qilong, the website, at:
>_________________________________________________________
>DO YOU YAHOO!?
>Get your free @yahoo.com address at http://mail.yahoo.com



Larry F website at: ~http://www.capital.net/~larryf/index  (see if I got it
right this time...good ol` copy and paste routine).