. Bulletin. Natural history; Natuurlijke historie. FIG. 78. Comparison of ungual form and mechanics of the second pedal ungual of Deinonychus (a) with the second manual ungual of Deinonychus (b), the first manual ungual of Allosaurus (c) and the third manual ungual of Ornitholestes (d). AH unguals are drawn to unit length so the ungual lever arms or radii of flexion (heavy dashed lines) are equal. The vertical lines to the left of each give the true scale in centimeters. The small dashed-line circles represent projections of the curvature of the articular facets on the penultimate phalanges. N
. Bulletin. Natural history; Natuurlijke historie. FIG. 78. Comparison of ungual form and mechanics of the second pedal ungual of Deinonychus (a) with the second manual ungual of Deinonychus (b), the first manual ungual of Allosaurus (c) and the third manual ungual of Ornitholestes (d). AH unguals are drawn to unit length so the ungual lever arms or radii of flexion (heavy dashed lines) are equal. The vertical lines to the left of each give the true scale in centimeters. The small dashed-line circles represent projections of the curvature of the articular facets on the penultimate phalanges. Notice the comparatively small angle between the cutting edge of the ungual and the arc of rotation of the Deinonychus pes claw (a) as compared with the others. See text for further discussion. All linear dimensions are in centimeters. a = Deinonychus antirrhopus, pes digit II, YPM 5205. b = Deiyionychus antirrhopus, digit II, YPM 5206. c = Allosaurus fragilis, manus digit I, USNM 4734. d = Ornitholestes hermanni, manus digit III, AMNH 587. are equal. The actual length of each lever arm is given in centimeters and the scale for each is shown by the heavy vertical lines. The cutting edge of the Deinonychus pedal ungual (Fig. 78a) forms a very small angle (25°) with the arc of flexion. A comparable or smaller angle must have existed with respect to the horny claw. Contrast this small angle with the much larger angle of attack of the other theropod unguals (Fig. 78c and d) and that of the second manus ungual of Deinonychus (Fig. 78b). It would appear that selection has shifted the angle of attack to more nearly coincide with the arc of attack of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Peabody Museum of Natural History. New Haven : The Museum
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