RE: sprawling dromaeosaurs?

["John R. Hutchinson" <jrhutch@rvc.ac.uk>]

Just a note on how my pelvic/femur work has been cited wrt the sprawling
deinonychosaur idea: I don't think it's terribly relevant to that, i.e., it
does not exclude many potential hypotheses, including (some) full-on
sprawling dromaeosaurs.

First of all, who knows how much sprawl would be enough for a glider to make
its hindlimbs into competent airfoils; 90 degrees of abduction (i.e., femur
sticking straight out laterally from hip socket) might not be needed. Only
calculations in some sort of dynamic model could really approach that issue,
imo.

Second of course there is the problem of interpreting 3D morphology and
articulations; I defer to those who have spent the time studying the actual
specimens as I don't trust my eyes with 2D photos/figures in such matters
and can't remember what I saw years ago when I had a look at "Archaeoraptor"
and other (then new) specimens. In my experience, osteology is just an
initial guide to what joint angles are/not possible, then soft tissues form
a second tier of constraints on top of bone-bone articulations. So bones may
not be a reliable guide in and of themselves, or they may; it depends.
[e.g., in our 2000 Paleobiology paper, Gatesy and I mentioned how osteology
only constraints bird hip abduction to ~60deg, and soft tissues constrain it
further; we inferred about 60-70 deg osteological limits in eumaniraptorans
but Microraptor etc. may well have been different; who knows -- depends in
particular on how one interprets the function of the antitrochanter in
articulations]

Third is the hip abductor muscle issue; I don't think that sheds much light
on whether or not such abduction would be possible or not. Aerodynamic
forces might compensate for what muscles can't do, and who knows if hip
abductors could have/not shortened enough to abduct the femur to whatever
degree of abduction was needed; I wouldn't go assume that 30% muscle
shortening is their maximum limit of abduction, as some might, for many
reasons.

Finally would be the dearth of information on how birds abduct their femora
(which they do, to a degree) -- what limits/enables abduction, etc.  Much
experimental work to be done there; mostly just a lot of anatomical work so
far.

Fun issue though, and deserving a lot more work to examine its relevance to
the origin of true flight.

Cheers,
John

============================================
John R. Hutchinson
Structure and Motion Laboratory
The Royal Veterinary College
University of London
Hawkshead Lane, North Mymms
Herts AL9 7TA, United Kingdom
phone  (+44) (0)1707-666-313
fax    (+44) (0)1707-666-371 or 652-090
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