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Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)



Okay, with the respect of the basal relative positions of Microraptor
and Archaeopteryx I was just referring to the reconstruction of the
ancestral character state on the length of the leg feathers.
Reconstruction of other character states in the ancestor of all
Paraves, such as relative femoral/hindlimb lengths, were not
considered by me but can be approached by the same parsimony
principle.

Jaime Headden wrote:

<… the avian femur is oriented slightly laterally to the vertical in
its crouched, neutral position, and to extend, the femur MUST abduct
outwards to move around the posteriorly swung gut, a side-product of
having an anteriorly-position center of gravity. This is not the case
in *Microraptor* It simply does not need to abduct the femur to walk,
and there is no reason it should.>

That birds have a bigger belly than Microraptor may suggest birds
should abduct more their femora as they retract them, but Hutchinson
and Gatesy (2001) rather indicate that in terrestrial locomotion,
during retraction the femur is, quite the opposite, adducted in birds.
In any case, whether there is no need to abduct the femur because of
lacking a wide belly does not indicate whether abduction is restricted
in a non-big-bellied taxon such as Microraptor.

<The argument that the semi-spherical caput with slightly elevated
neck over the trochanteric body of the femur is an old one, and has
been argued to be inconclusive due to distortion of the Hwang et al.
specimens. It is simply not informative to argue that the positions
and preservation are identical to the living animal, and thus we can
only argue for what we can compare and derive in other, less distorted
fossils.>

I am with you in this, but I think that deformation does not permit
either to hypothesize greater or lesser abducting powers than in
birds. Indeed, in birds the trochanter femoris is many times even more
proximally located than the femoral head, yet there seems to be no
problem for abduction.

<These tell us that the femur and the ilium are conjoined so much more
closely than in birds, especially given the perforate acetabulum, such
that the femur inserts deeply into the hip socket.>

But birds also have a perforate acetabulum, yet it does not trap the
femoral head, or restrict in any way its movements. Neither does it
seem this was the case in other dinosaurs. At least in Neornithes it
even permits further movements such as letting some parts of the head
to become more medially located in movements such as rotation along
the femoral long axis.

<Eversion, as Scott Hartman has demonstrated in the past few times
this argument has come up, causes dislocation of the hip, and that's
even using the preserved conditions of the femora and ilia. The
natural conditions, if they are different from the preserved ones,
would likely further prevent dislocation. Maybe Scott would be willing
to post a link showing the illustration? This is based on the natural
case, and is compared to the femora and ilia of other dromaeosaurs.>

I agree that femoral abduction (your eversion, I suppose) tends to
dislocate much of the articular surfaces of the antitrochanter and
facies articularis antitrochanterica, even in the pigeon, and so
likely also in other paravians, but the caput femoris still maintains
contact with the more cranial, not antitrochanteric, part of the
acetabular surface. This cranial part of the acetabular surface is
present in deinonychosaurs, where the femoral head is also rounded
(e.g., Velociraptor, Norell and Makovicky, 99'; Deinonychus, Ostrom
76')

The disarticulation between antitrochanter and facies articularis
antitrochanterica is not damaging sensu Cracraft (71'), and in absence
of contrary evidence, I do not see why would it be more damaging in
other paravians, where the position of both the antitrochanter and
facies articularis antitrochanterica are comparable (Norell and
Makovicky 99').

<Because in normal avian terrestrial locomotion, the femur barely extends>

Not in fast running, where the femur engages considerable retraction,
however, I suppose not the sufficient to permit disarticulation
between antitrochanter and facies articularis antitrochanterica.

<Such a dorsal shelf does not neccessarily have to be large to reduce motion.>

True, but in Velociraptor, as in birds, the supraacetabular crest is
not present in the most caudal part of the acetabular dorsal border.
As there are no ventral views of the Microraptor ilium, I infer the
basal condition in Paraves from Neornithes and Velociraptor, which
coincide in this point.

<Both crocs and birds have a naturally retracted femur as their
neutral condition. This is not true of non-avian dinosaurs.>

The neornithean femur most of the times points anteriorly and a little
laterally, so I think they have a normally protracted femur.

<The mere presence of a derived supracetabular shelf, the large and
sometimes extremely large trochanteric body of the femur, the medially
oriented caput, the cylindrical structure of the latter, and most
certainly the perforate acetabulum with a deep interlock between
pelvis and femur indicate that the femur was constrained in virtually
all non-avian dinosaurs to parasagittal motion.>

First, to parasagittal retraction must be added long-axis rotation, as
indicated by Hutchinson and Gatesy (2001). Second, between the
antitrochanter and the supraacetabular there is, in both basal and
paravian dinosaurs, a cleft, where the greater trochanter can be
medially rotated if the dinosaur wanted (even if not used in
locomotion). Third, as I said before, the acetabular perforation does
not trap the femoral head to a strict parasagittal anteroposterior
motion, and just the long axis rotation by itself requires some more
freedom of movements. Fourth, the dinosaurian acetabular surface does
not perfectly fit around a cylinder formed by the proximal articular
surface of the femur. Such a perfect fit can be found in the elbow of
ungulates such as horses and cows, where it is not possible to make
other movements than flexion-extension: no such a perfect fitting
exist in the dinosaurian coxo-femoral articulation. The acetabular
surface in dinosaurs is never so tighly wrapped around the femoral
proximal surface as to limit its movements in a single direction.

<These no NOT indicate than a croc derivative (but not necessarily the
originating croc condition! -- See work on *Terrestrisuchus* and other
crocodylomorphans for derivatives of highly terrestrial and
erect-postured crocs) must represent the constraint for the
originating dinosaurian condition, from which birds must derive, if
birds arrive at their correct condition by modifying their hips to a
similar condition. They did not
 retain that condition through their derivation from the bird-croc
ancestor, and this is the important thing that sets this issue apart
from the EPB.>

I just checked Terrestrisuchus and it does not present anything quite
restrictive. Sure, it has a supraacetabular crest, but there is no
well-marked caput femoris, nor apparent restriction of abduction, nor
is there in other basal archosaurs without the caput. The primitive
state for archosaurs seems to be not having a well developed caput
femoris. It seems that such a medially directed caput appeared
independently in dinosaurs, Lagerpeton+Dromomeron, poposaurs, and
perhaps Fasolasuchus and some aetosaurs.

Sure that extant archosaurs are not exactly the same in coxo-femoral
anatomy than their extinct fellows, or even the states we can
reconstruct for their ancestors. But when movements are not clearly as
restricted as in the cow elbow, and where there is the possibility of
a movement (which is an attribute only extant taxa possess) present in
the extant outgroups of the extinct taxon, I think we should apply the
EPB and infer the extinct taxon at least had the capacity of
performing that movement, even if it did not. To me, to put the EPB
apart of this discussion would be justified if we have such a tight
articulation as that of the cow elbow, where there is no physical way
we can find other movements. The dinosaurian coxo-femoral articulation
is not like this and does not form a perfect hinge-joint. Its range of
motion is reduced when compared with a crocodile, but that does not
mean abduction was not possible.

Cheers.

Augusto Haro.