Table 1.
MANOVA of partial warp scores which collectively describe the shape of the humerus and femur in the samples.
Figure 1.
Landmarks digitized for 2-D thin-plate splines (TPS) geometric morphometrics (GM) analyses – Mammals.
All drawings are not to scale and were enlarged or reduced to facilitate comparisons. For the humerus, landmarks 1 and 2 encompass the region between the greater tubercle and the medial extent of the humeral head. Landmarks 2, 3, and 4 encompass the extent of the deltopectoral crest. Landmarks 4 and 7 encompass the narrowest point of the midshaft. Landmarks 5 and 6 denote the lateral and medial epicondyles, respectively. For the femur, landmarks 1 and 2 encompass the region between the greater trochanter and the medial extent of the proximal end of the femur. Landmarks 3 and 6 encompass the narrowest point of the midshaft. Landmarks 4 and 5 denote the the lateral and medial epicondyles. Regions of sub-articular bone are indicated in dark gray and the digitized outlines that were subsequently converted into chains of 10 evenly-spaced semi-landmarks are colored red. The exemplar taxa represented as bones, left to right, are: Ornithorhynchus, Mammut, and Paraceratherium. The TPS reference forms which describe the shape of the bones mathematically is shown at right.
Figure 2.
Landmarks digitized for 2-D thin-plate splines (TPS) geometric morphmetric (GM) analyses – Archosaurs.
All drawings are not to scale and were enlarged or reduced to facilitate comparisons. For the humerus, landmarks 1 and 2 encompass the region of the humeral head. Landmarks 2, 3, and 4 encompass the extent of the deltopectoral crest. Landmarks 4 and 7 encompass the narrowest point of the midshaft. Landmarks 5 and 6 denote the lateral and medial epicondyles, respectively. For the femur, landmarks 1 and 2 encompass the region of the femoral head. Landmarks 3 and 6 encompass the narrowest point of the midshaft. Landmarks 4 and 5 denote the the lateral and medial epicondyles. Regions of sub-articular bone are indicated in dark gray and the digitized outlines that were subsequently converted into chains of 10 evenly-spaced semi-landmarks are colored red. The exemplar taxa represented as bones, left to right, are: Alligator, Torneria (“Barosaurus”), and Allosaurus. Given that birds were included in the Archosauria sample, the fourth trochanter (4 Tr) was not digitized. The TPS reference forms which describe the shape of the bones mathematically is shown at right.
Figure 3.
Changes in humerus shape in mammals.
Maximum humerus shape change in the sample is shown on the Y-axis (PRIN 1), whereas humerus shape changes associated with size are shown on the X-axis. Note that on the PRIN 1 axis, monotreme taxa plot separately from other mammals in the sample, and show a much more expanded and robust humerus. On the X-axis, the sub-articular bone region narrows significantly with increasing size, and the shapes of these regions become more convex and/or distinct.
Table 2.
Kruskal-Wallace and pair-wise Mann-Whitney U non-parametric tests for significant differences in maximum shape change (PRIN 1) among the sampled taxa based on the median score of PRIN 1.
Table 3.
Kruskal-Wallace and pair-wise Mann-Whitney U non-parametric tests for significant differences in maximum shape change (PRIN 1) among the postures of the sampled taxa based on the median score of PRIN 1.
Table 4.
Multiple and multivariate regression of partial warps on size (humerus or femur maximum length).
Figure 4.
Changes in femur shape in mammals.
Maximum femur shape change in the sample is shown on the Y-axis (PRIN 1), whereas femur shape changes associated with size are shown on the X-axis. As with the humerus, monotreme specimens plot among the most robust femora on the PRIN 1 axis, but aardvarks, rhinos, and one Paraceratherium specimen also plot in robust morphospace. Once again, the sub-articular bone region narrows significantly with increasing size and that the shapes of these regions become more defined, convex, and/or distinct. Notice also that the femoral head becomes more distinct and medially-oriented with increasing size.
Figure 5.
Changes humerus shape in saurischian dinosaurs and alligators.
Maximum humerus shape change in the sample is shown on the Y-axis (PRIN 1), whereas humerus shape changes associated with size are shown on the X-axis. Changes in humerus shape along the PRIN 1 axis and X-axis are similar in that larger taxa have more proximally and distally expanded ends. In particular, the sub-articular region expands tremendously whereas its overall shape remains gently convex. Note also that the deltopectoral crest (landmarks 2–4) remains or becomes more medially-deflected as size increases.
Figure 6.
Changes in femur shape saurischian dinosaurs and alligators.
Maximum femur shape change in the sample is shown on the Y-axis (PRIN 1), whereas femur shape changes associated with size are shown on the X-axis. As with the humerus, changes in femur shape along the PRIN 1 axis and X-axis are similar in that larger taxa have more proximally and distally expanded ends. Overall, the sub-articular region expands tremendously whereas its overall shape remains gently convex, although the distal condyles become somewhat more pronounced.
Figure 7.
Schematic representation of changing joint surfaces and articular cartilage thickness with increasing size in mammals and archosaurs.
Our data suggest that as mammals increase in size, the joint region narrows and the articular cartilage becomes relatively thinner, producing convex and well-developed subchondral bone surfaces. For archosaurs, our data suggest that with increasing size the joint region expands while the articular cartilage remains thick, producing relatively flat and less convex subchondral bone surfaces.