[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Jaime's ptero art




"Jaime A. Headden" wrote:

> David Peters (davidrpeters@earthlink.net) wrote:
>
> <Generalizations are almost always bad.>
>
>  Yes, in some regards. But I was making a general statement with respect
> to my statements, clarified in the same paragraph. I have found that so
> far, very few taxa exceed 45 degrees upward slope of the torso when the
> given arm and leg lengths are used as walking aparatus. My arm
> measurements start at the radius, and I draw the rest down through the arm
> to the fourth metacarpal-phalangeal joint, which I raise just above the
> ground (no tracks have yet to show it in regular locomotion). The humerus
> is left as horizontal, so the glenoid height off the ground is almost
> always the length of the forearm minus the wing digit, and with the digits
> 1-3 slightly elevating the arm up (as seen in tracks).

DP: All good. One thing that happens when you raise the verts is that the elbow 
drops as the humerus stays within the plane of the torso.


> The leg is measured
> from femoral caput to ankle, which touches the ground (as shown in tracks
> of pterodactyloids). In taxa for which a long fifth digit is known, I have
> both alternately oriented the pes about 45 degrees up, or laid it flat,
> but it doesn't change the length measurement by a significant degree
> except in the basalmost known pterosaurs. Femoral lateral eversion also
> affect leg length somewhat, and I try in most of my reconstructions to
> articulate the femur with this eversion evident, so that would shorten the
> leg by about 5% of the femoral length or so.

DP: All good.

>
>   So, in my work, I find that some taxa have extraordinarily long arms
> relative to wings in the radio/metacarpal measurement, and some don't. And
> there doesn't seem to be much of a phylogenetic signal: Taxa showing
> nearly horizontal postures include *Beipiaopterus,* *Dimorphodon,*
> *Eosipterus,* *Pterodactylus,* *Dorygnathus,* *Scaphognathus,*
> *Austriadactylus,* *Dendrorhynchoides,* and I am betting one or two others
> based on relatively good skeletons (including *Quetzalcoatlus* sp., but
> this is based on Paul's skeleton and not my measuring). Taxa that incline
> upwards of about 5-10 degrees include: *Anhanguera,* *Dsungaripterus,*
> *Jeholopterus,* *Anurognathus* and a few more I'm sure. I found that
> *Pterodaustro* as well as *Nyctosaurus,* incline at or above 45 degrees
> (*Pteranodon* and *Nyctosaurus* share a nearly 60 degree angle). I looked
> at *Gallodactylus*/*Cycnorhamphus* (the Quentstedt specimen), and it looks
> like it may include up about 5 degrees or so, based on the arm to femur
> morphology. Because of this, I can safely infer that more than half the
> pterosaurs known were likely horizontal in orientation.

DP: An index to Jaime's must-see artwork can be found at:

http://www.freewebs.com/skeletaldatabase/jaimeheadden.htm

By the way, and for the record, as I've said to you privately, Jaime, your 
artwork and skills are outstanding! I would urge all DMLers to take a look. 
Jaime's a force to be reckoned with and is an important contributor and player.

Okay, Jaime, here it comes with all best wishes and respect, a short critique:

Beipiaopterus: The pelves and prepubes are present. Just hard to see. The pubes 
and prepubes have a strong anterior incline, and so should the femur in a 
standing configuration. When you realign your femora anteriorly (still splayed
though), the posterior will drop a bit. Still the spine in this taxon is not 
more than 40 degrees above the horizon. Your humeri are abducted too far. Your 
antebrachia are overextended. When walking the forelimbs contribute most of 
their
motion by opening and closing at the elbow. Weird but true. (see 
pterosaurinfo.com > behaviors for an animation). To abduct the humeri to the 
degree that you have done is to make the fingers too anteriorly oriented. In my 
3D full scale
Pteranodon the humeri divege from an angle with a vertex at mid neck, about 35 
degrees from the midline. Brown, Baumel and Klemm have shown that in birds the 
propatagial ligament prevents over extension due to drag forces in flight. The
same holds true for pterosaurs. There is a limit to elbow extension that cannot 
be exceeded as you and others appear to have done in reconstructions.

Dimorphodon:  For some reason your antebrachia are way too short. Manual 4.1 
should only reach mid ulna. And no animal walks with both feet behind its 
pelvis except dads chasing toddlers. Try to take your pterosaur through a 
complete
animated walk cycle, as I have done, and see what problems you'll have. Plus 
Clark et al. would not like to see your metatarasals elevated to the vertical. 
Comments regarding aligning your femora with the prepubis apply here too. It's 
the
adductor anchor that keeps the femora from over spreading.

Dorygnathus: Not sure which specimen is shown here. In all Dorys the feet are 
more than half a tibia in length and pedal 5.2 is much longer and more bent 
than you indicate. Coments from above apply here.

Another benefit to placing pteros in a more upright stance is it gets the toes 
beneath the humeral glenoids, ideal for quick getaways and for 
folding/unfolding those big wings in a hurry. Sooner or later your Dory is 
going to have to get
on its hind feet to unfold its wings. Why not all the time?

Similar comments on Jeholopterus. The prepubis should be way anterior, and so 
go the femora. Humeral abduction too far out. Feet too small. etc.

I think the patterns are pretty well established and noted and there's no need 
to belabor this. The key is get the feet under the body in a standing 
configuration. If walking at least one foot in front of the pelvis as one drops 
behind, as
in all tetra pods. Remember, to get those wings originally, pteros had to go 
through a strictly bipedal phase at sometime in their phylogeny. The forelimbs 
had to be freed up to do something else to get what they got. If they were 
always
weight bearing, you'll have to come up with a good explanation and a 
phylogenetic scenario for those lateral to posterior three fingers, and that 
big awkward fourth finger.

If I missed any taxa you want a comment on, please let me know. I enjoy your 
artwork immensely.

Best and all good will,
David Peters
St. Louis