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Scansoriality in Some Jehol Theropods
Okay, the main thrust and the source of this study was *Epidendrosaurus*,
which I include *Scansoriopteryx* under provisionally. I think the date
issue has not been solved, either way. Nonetheless, it is my opinion they
are the same animal, and I use them comparatively.
This is a question of claw curvature. In predatory terrestrial cursors
among dinosaurs (such as *Deinonychus*), the manus claws are more curved
than the pedal claws that touch the ground. In arboreal animals, the pedal
claws are further curved, so that they approximate the manus in curvature
and shape. I compared the claws of the IVPP and CAGS specimens and found
thy approximate each other in shape. Keratinous sheaths are present on the
claws in the CAGS specimen, and these exaggerate the shapes only slightly.
The bony claws are roughly the same shape and curvature, whereas the
keratin shows a different pattern. The pedal claws indicates a long taper,
whereas the manus claws a shallower, deeper, and shorter curve.
To compare, claws in *Microraptor* and *Cryptovolans* have similar bony
cores, and the claws of NGMC 91 (Dave, described as similar to
*Sinornithosaurus*) have distinctly different curves wether pedal or
manus. The the last, the pedal claws are shallower, and the keratin
reflects this, while the manus claws of Dave, Micro, and Crypto are all
strongly curved equally. *Microraptor* varies only in having slightly less
curved manus claws, as in *Epidendrosaurus*, though the keratin is very
slender and narrow. Pedal claws in *Epidendrosaurus* show the keratin in
the pedal claws is more than 50% the bone length, whereas the manus it is
30%; in Dave, the sheaths are of equal proportion.
Curvature in claws of extand birds show a distinction in habitat versus
curvature. The shallower the curve, the more terrestrial, strong curves
indicate arboreal habits, and intermediate curves with a greater dorsal
curve versus the ventral (Yalden, 1982, 1986; Feduccia, 1996) indicate
scansoriality. In *Epidendrosaurus*, the pedal claws are strongly curved
in the arboreal class, the manus in the terrestrial margin. For
*Microraptor* and *Cryptovolans*, they are both sharply curved, and Dave
has shallower, scansorial pedal and arboreal manus claws. One comparison
may be the curvature increases in predatory use in the limbs, suggesting
both the smaller "sinornithosaurs" Micro and Crypto were fully equipped
branch climbers and "scamperers" which would have hunted in the branches
for prey, effected by their large shallowly-curved crowns; Dave and the
larger "sinornithosaur" were branch climbers and may have ambushed much
larger prey, their teeth were smaller relative to their jaws and recurved
greater, making short work of prey in slashing bites. Epidendro appears to
have been a bipedal scamperer, it's manus claws not well shaped for branch
grasping, and its manus digits abberantly elongated. it may have used the
manus for manipulation and climb more than prey grappling or branch
grasping. I envision this animal close to the trunk in the midst of
branches, small sinornithosaurs out in the branches or higher, and
Jaime A. Headden
Little steps are often the hardest to take. We are too used to making leaps
in the face of adversity, that a simple skip is so hard to do. We should all
learn to walk soft, walk small, see the world around us rather than zoom by it.
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