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Ornithoms, Parrots, and others



A double reply posting:
In reply to Jaime A. Headden:
>  Appologies to Tom and the list about mentioning ornithomimosaur taxa
>that hadn't been defined. I hadn't known about the "Ornithomimoidea"
>not being a properly-defined taxon, and should have checked my
>resources.

Not a problem, but just a general warning to the readership: a fair number
of names bandied about the list have not been formally proposed yet.  Please
be careful with using them, citing them, using them on websites, etc.

>  As for the parrot thread, I only meant to suggest a comparative
>fossil, but as I have no paleo-ornithological knowledg aside from what
>I've glanced at in some related paleo books and articles (Feduccia,
>Chatterjee, Gatesy), I should have kept my big mouth shut. :)

Okay, I apologize, too, for overreacting a bit.  Still, (as I said before)
it would be nice to see people examine the evidence first before making
conclusions.  (As I also noted, I made the same conclusion as did George and
Jaime, that the parrot was a caenagnathid, before seeing the paper.  Still,
I waited to see the info before posting, which was a good thing, as Stidham
does find some features that are inconsistant with it being a caenagnathid,
but supporting a parrot identity).

At 11:02 PM 11/9/98 -0000, John Jackson wrote:

>It is through these differences that I believe a useful probabilistic test
of some kind might be made. Something ?very maniraptoran? did exist - it had
to, to give rise to Archae. However I predict that none of the types found
in the K will be found pre Archae.

I'll accept that prediction, and add in its stead that the next decade will
likely see the following in Jurassic rocks: basal oviraptorosaurs, basal
dromaeosaurs, basal bullatosaurs (if this remains a distinct clade within
Maniraptoriformes: if not, both proto-troodonts and proto-ornithomimosaurs),
and basal tyrannosaurids.

>Archae?s close ancestors will have been spinning off larger, non-arboreal
forms presumably, in the way George has described, and some of these will be
found. Perhaps the specimen Tom describes as maniraptoran was one of these
(though notice, it has not been possible to say for certain exactly which
type it belonged to ? ?probably troodont hips/legs? I believe). 

I have yet to receive my copy of the Morrison Symposium volumes, in which
Padian has an update, but when Jensen & Padian described the fossil (a right
femur), they could not distinguish whether it was from an early bird or a
deinonychosaur, and so considered it simply as maniraptoran.  (Jensen, J. &
Padian, K. 1989. Small pterosaurs and dinosaurs from the Uncompahgre fauna
(Brushy Basin Member, Morrison Formation: ?Tithonian), Late Jurassic,
western Colorado.  J. Paleontology 63: 364-373).

>This clade will consist of creatures with feathers or feathered ancestors.
I?m going to call its members "Pinnants", though for absurd and iniquitous
reasons I would be prevented from publishing it "formally".

Yeah, we know, everyone is out to get you, blah, blah, blah...  Of course,
IF you had a new group to name which could clearly be distinguished as a
distinct clade, then I'd be happy to see you publish it.  Do you?  (A word
of interest: the clade defined as all descendants of the most recent common
ancestor of _Oviraptor_ and Neornithes has not been formally (or at least
properly) named, and almost all recent analyses show that this grouping
(which also includes dromaeosaurids) IS pretty well supported and IS a
distinct group from the more-inclusive Maniraptoriformes and MAY WELL be
characterized by true feathers.  So, see, you can play the game the way
others do, and still get your clade named!).

>I?m fully aware of the disgraceful situation, I can assure you, and I?m not
going to be gagged by it. Don?t bother to complain ? I?m going to carry on
using Pinnants, and if I get thrown off the list because of it, then you?re
all PATHETIC!

Pathos is in the eye of the beholder.

>What you should be doing is pressing for the odd small but significant
change to the peer review system. ("Birds" would be a better name, but it?s
too confusing.) Of course, all this rather depends on whether my theory of
feathers is right, so if it?s of any comfort, you can regard it as a
hypothetical clade.

Fair enough.

>Tom said:
>
>>A ) Hooking and pulling is EXACTLY the type of "killing blow" proposed for
>the maniraptoriform hand by Gauthier & Padian: please read the paper. It
>has nothing to do with bear-like power slaps: it is simply a method to
>rapidly acquire the prey so that other parts (jaws, foot claws, etc.) can
>dispatch the prey.
>
>Why did eg _Deinonychus_ need relatively much longer and more powerful arms
for catching its prey than say _Allosaurus_? And why did it need its
shoulder joints so much nearer the backbone?

Ah, good old fashioned "why" questions.  Come, come, please remember that
the proper answer to "why" questions in evolutionary biology is "why not?".

"What" questions, though, can at least be approached.  And "what advantage
would a dromaeosaurid forelimb give over a more basal tetanurine forelimb?"
How about: reach, while at the same time the ability to fold it against the
body while not in use; speed of deployment; range of motion, particularly at
the shoulder blade; and possibly for climbing.

>(And why the backward pointing pubis and the stiff tail?)

Reorganization of the hindlimb musculature from a tail-driven to a
knee-driven system? Increased use of the tail as a dynamic stabilizer?

>The arms are very powerful ? too powerful for just holding the prey back.

Too powerful?  In what way?  Add power to the system, and you can start
incorporating additional items in the menu.

>Not just powerful enough to climb up onto the prey, in fact, if you compare
the muscle attachment flanges on the humerus for _D_ with a human, who may
be able to pull himself up by his arms alone, there is an enormous extra
capacity.

Ooh, danger territory here.  Comparing primate and dinosaur forelimb and
musculature can be VERY tricky: we are built in very different ways.  Yes,
dromaeosaurs have much bigger deltapectoral crests than humans, no question.
And exactly which groups of mammals HAVE big deltapectoral crests?
Furthermore, our forelimbs have much greater rotational ability at more
joints than a theropod forelimb.  We are both specialized in very different
ways (but potentially for very similar reasons: among them, grasping and/or
arboreal ancestry).

>Useful for climbing on prey, but why did it evolve this enormous
overcapacity in the first place? They use the phrase *killing blow* but you
say *other parts* would dispatch the prey. Either you disagree with them, or
there would seem to some uncertainty in their minds.

Actually, where do they use the phrase "killing blow"?  I was using your own
phrase, but 
Gauthier & Padian do not use that terminology in their paper on the subject
(Gauthier, J. & Padian, K. 1985. Phylogenetic, functional, and aerodynamic
analyses of the origin of birds and their flight. pp. 185-197. In, Hecht,
M.K., Ostrom, J.H., Viohl, G. & Wellnhofer, P.  The Beginnings of Birds).

As we have talked about (here and elsewhere), you seem to misunderstand
their hypothesis.  It is not a bear- or lion-like power slap that is being
invoked, but simply a rapid and extended predatory grasp.

Hope this helps.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661