Details of the skeletal samples, measurements, and some of the statistical analyses have been reported previously in Lemelin (1996, 1999). For the purpose of this chapter, the methods and some of the results of these analyses are summarized, in addition to new morphometric results. Five didelphid taxa (Monodelphis domestica, Philander opossum, Didelphis virginiana, Marmosa robinsoni, and Caluromys philander) and three cheirogaleid taxa (Microcebus murinus, Cheirogaleus medius, and Cheirogaleus major) were considered. The sample sizes are indicated in Figures 3 and 4. The length of each metapodial (M), proximal phalanx (PP), and middle phalanx (MP) was measured on the hands and feet of museum specimens (skeletal specimens or radiographs of pelts). A phalangeal index was computed in order to estimate the degree of pre-hensility of each ray (I-V) (Napier and Napier, 1967; Napier, 1993). For the first ray of the hand and foot, this index is equal to the length of the PP divided by the corresponding M times 100. For all other rays, the same index is equal to the sum of the PP and MP divided by the corresponding M times 100.

When examining the means and spread of the data within didelphid marsupials, the same basic pattern repeats itself for all rays (with the exception of the hallux): Marmosa and Caluromys, two fine-branch arborealists, have significantly higher phalangeal indices compared to the more ground-dwelling Monodelphis, Didelphis, and Philander (see Lemelin, 1996, 1999 for details of the statistical results) (Figures 3 and 4). In other words, didelphids that rely on terminal branches or vines when moving and foraging have more prehensile hands and n = 7 n = 6 n = 14 n= 10 n= 11 n= 10 n= 10 n = 9

Ray V

n = 7 n = 6 n = 13 n = 10 n = 11 n = 10 n = 10 n = 10

Ray IV

200%

200%

200%

200%

200%

Figure 3. Box-plot graphs of the phalangeal indices for rays I through V of the hand in didelphids and cheirogaleids. The diamonds represent the mean, the vertical line the median, the left and right sides of the rectangle the 25th and the 75th percentiles, and the left and right ends of the horizontal line the 10th and the 90th percentiles. The shaded rectangles represent taxa that move and forage primarily on thin branches and open rectangles that move and forage primarily on large arboreal substrates and/or the ground. (1)

Monodelphis brevicaudata, (2) Philander opossum, (3) Didelphis virginiana, (4) Marmoset robinsoni, (5) Caluromys philander, (6) Microcebus murinus, (7) Cheirogaleus medius, and (8) Cheirogaleus major.

200%

Figure 3. Box-plot graphs of the phalangeal indices for rays I through V of the hand in didelphids and cheirogaleids. The diamonds represent the mean, the vertical line the median, the left and right sides of the rectangle the 25th and the 75th percentiles, and the left and right ends of the horizontal line the 10th and the 90th percentiles. The shaded rectangles represent taxa that move and forage primarily on thin branches and open rectangles that move and forage primarily on large arboreal substrates and/or the ground. (1)

Monodelphis brevicaudata, (2) Philander opossum, (3) Didelphis virginiana, (4) Marmoset robinsoni, (5) Caluromys philander, (6) Microcebus murinus, (7) Cheirogaleus medius, and (8) Cheirogaleus major.

r rt

n=7 |
(8) tc- |
n=7 |
œ- | ||||||||||||||||||||

n=6 |
(7) |
n=6 |
m | ||||||||||||||||||||

n=12 |
(6) M— |
n=12 |
-DE— | ||||||||||||||||||||

RaVV n=11 ~ |
m |
Ray IV | |||||||||||||||||||||

n=8 |
(3) œ |
n=8 |
ai- | ||||||||||||||||||||

n=10 |
(2) —e- |
n=10 |
-» | ||||||||||||||||||||

n=10 |
(V » |
n=10 |
n |
200% 200% 200% 200%
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