Thursday, December 2, 2010

Pterosaur wrist (5)

More on the pterosaur wrist.

Fig. 4. (A) Lateral view of the right medial carpal in articulation with the distal carpal of the Cretaceous pterosaurColoborhynchus robustus. Scale bar, 25 mm. (B) Traditionally recognised articular surfaces of the right carpal-pteroid joint of Coloborhynchus, the medial carpal in distal (anterior) view showing the fovea (fov), and the head of the pteroid in proximal view. Specimen details can be found in Wilkinson et al. (Wilkinson et al., 2006Go). Scale as in A. (C) Reconstruction of the right wrist of Coloborhynchus in dorsal view according to descriptions provided by Bennett (Bennett, 2001Go; Bennett, 2006Go), with a sesamoid bone (ses) within the fovea, and the pteroid articulating on the side of the medial carpal. Note that the medial carpal has been rotated about its long axis by 180° with respect to A and B. The postulated trajectory of the wing-finger metacarpal extensor tendon (ten), in which the sesamoid is embedded, is also shown. Scale bar, 50 mm. (D) Reconstruction of the right wrist in dorsal view according to Wilkinson et al. (Wilkinson et al., 2006Go), with the pteroid at maximum elevation, and an alternative reconstruction of the sesamoid, which is shown in close association with the carpal-pteroid joint, embedded within a putative pteroid extensor tendon (origin and insertion points unknown). Scale as in C. Abbreviations as in Fig. 1. Broken line indicates a continuation of the extent of the tendon. Additional abbreviations: dc, distal carpal; f, femur; h, humerus; mc, medial carpal; pc, proximal carpal; r, radius; t, tibiotarsus; u, ulna; wf, wing-finger; wm, wing-finger metacarpal.

Summary of pictures:


FIGURE 5. Photographs of A, the left (above) and right (below) carpal regions of Anhanguera santanae, AMNH 22555, in dorsal view, slightly disarticulated but in situ during preparation; B, the right preaxial carpal, Sesamoid A, and pteroid of Pteranodon sp. indet., YPM 2300, in dorsal or lateral view; and C, non-rticular (left) and articular (right) surfaces, respectively, of Sesamoid A of Pteranodon longiceps, YPM 1175. Abbreviations: art, articular surface for fovea; asp, articular surface for pteroid; ds, distal syncarpal; mciv, metacarpal IV; pc, preaxial carpal; ps, proximal syncarpal; pt, pteroid; r, radius; str, striations for attachment to its tendon; u, ulna; and sesA, Sesamoid A. Photograph of AMNH 22555 courtesy of P. Wellnhofer.

The pterosaur forelimb. Black - humerus, yellow - radius & ulna, orange - pteroid, blue - metacarpals, white - phlanges of digit IV (4th phalanx not shown).


Left picture - Deinonychus antirrhopus:
PDF pictures cannot be copied here unfortunately.
Deinonychus antirrhopus: Page 97. 
Dinosaur hands Page 98
Notice how the dinosaur metacarpals are VERY similar
 to the pterosaur metacarpal. 

Series of primitive bird hands.


ALLOSAURUS  (dinosaur)


Arm section

1. Upper arm - humerus
2. Sesamoid bone - os sesamoides.
3. Ulna - ulna
4. Radius - Radius

Hand section (manus)

5. Wrist - radiale and ulnare
6. Metacarpal - carpometacarpus
7. Thumb - alula
8. Digits - phalanges

Metacarpal to phalanx articulation (hinge joint)
Unfortunately the picture from the pdf cannot be copied here. See drawing of bird wing - particularly the alula.


Diagram 4
1Ball and socket joint2Condyloid joint (Ellipsoid); 3Saddle joint4 Hinge joint; 5:Pivot joint;


Head of Metacarpal Bones:

The head is provided with a surface for articulation with the proximal phalanx. This area curves farther over its anterior aspect than the posterior. It is convex from before backwards and from side to side and is wider anteriorly than posteriorly. It is notched on its anterior aspect and its edges form two prominent tubercles, which are sometimes grooved for the small sesamoid bones.

First metacarpal bone:

The first metacarpal differs from the others in being free at its distal end. Its proximal end possesses only a carpal articular facet and is not articulated with other metacarpal bones. The first metacarpal bone is the shortest and stoutest of the series. Its body is compressed from before backwards. Its head is of large size and is grooved on its anterior aspect for the sesamoid bones. The base is provided with a saddle-shaped surface for articulation with the trapezius.
The wing of a modern bird, for example, has only two remaining carpals; the radiale (the scaphoid of mammals) and a bone formed from the fusion of four of the distal carpals.[14]
Drs. Alan Feduccia and Julie Nowicki of the University of North Carolina at Chapel Hill have done just that. They opened a series of live ostrich eggs at various stages of development and found what they believe is proof that birds could not have descended from dinosaurs. They also discovered the first concrete evidence of a thumb in birds.

"Whatever the ancestor of birds was, it must have had five fingers, not the three-fingered hand of theropod dinosaurs," Feduccia said. "Scientists agree that dinosaurs developed 'hands' with digits one, two and three -- which are the same as the thumb, index and middle fingers of humans -- because digits four and five remain as vestiges or tiny bumps on early dinosaur skeletons. Apparently many dinosaurs developed very specialized, almost unique 'hands' for grasping and raking. "Our studies of ostrich embryos, however, showed conclusively that in birds, only digits two, three and four, which correspond to the human index, middle and ring fingers, develop, and we have pictures to prove it," said Feduccia, professor and former chair of biology at UNC. "This creates a new problem for those who insist that dinosaurs were ancestors of modern birds. How can a bird hand, for example, with digits two, three and four evolve from a dinosaur hand that has only digits one, two and three? That would be almost impossible."
If one views a chicken skeleton and a dinosaur skeleton through binoculars they appear similar, but close and detailed examination reveals many differences, Feduccia said. Theropod dinosaurs, for example, had curved, serrated teeth, but the earliest birds had straight, unserrated peg-like teeth. They also had a different method of tooth implantation and replacement.

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