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. Author manuscript; available in PMC: 2011 Apr 26.
Published in final edited form as: J Hum Evol. 2009 Oct 28;57(6):710–720. doi: 10.1016/j.jhevol.2009.06.001

Table 2.

Means (± standard errors) for size-adjusted architectural variables for Cebus apella, C.albifrons, and C. capuchinus and Mann-Whitney U-test results of hypothesis tests comparing C.apella to the two untufted capuchins.

Cebus apella Cebus
albifrons 		Cebus
capuchinus 		C. apellavs.
untufted capuchinsa,b
Hypothesis 1:
Superficial Masseter Muscle
PCSA0.5/Jaw lengthc 0.080 ±0.010 0.057 ±0.012 0.049 ±0.011 C. apella > 0.0578
PCSA/Muscle weight 2.647 ±0.225 2.187 ±0.327 2.028 ±0.453 C. apella > 0.0860
Pinnation angle (°) 18.07 ±2.54 19.87 ±0.58 14.33 ±3.77 NS
Mass/P0 0.541 ±0.049 0.419 ±0.047 0.482 ±0.125 NS
Deep Masseter Muscled
PCSA0.5/Jaw length 0.021 ±0.003 0.017 ±0.007 0.012 ±0.004 C. apella > 0.0567
PCSA/Muscle weight 1.254 ±0.335 1.202 ±0.362 0.902 ±0.324 NS
Mass/Po 0.368 ±0.034 0.263 ±0.016 0.515 ±0.131 NS
Whole Masseter Muscle
PCSA0.5/Jaw length 0.109 ±0.011 0.078 ±0.020 0.062 ± 0.014 C. apella > 0.0199*
PCSA/Muscle weight 3.446 ±0.230 2.815 ±0.561 2.415 ±0.565 C. apella > 0.0592
Mass/Po 0.460 ±0.038 0.370 ±0.026 0.465 ±0.130 NS
Temporalis Muscle
PCSA0.5/Jaw length 0.147 ±0.017 0.085 ±0.022 0.072 ±0.012 C. apella > 0.0055
PCSA/Muscle weight 3.719 ±0.299 2.525 ±0.458 2.325 ±0.408 C. apella > 0.0038
Pinnation angle (°) 12.42 ±1.46 10.18 ±0.99 7.60 ±2.30 NS
Mass/Po 0.660 ±0.061 0.582 ±0.065 0.666 ±0.145 NS
Hypothesis 2:
Superficial Masseter Muscle
NLf/Jaw lengthc 0.181 ±0.015 0.152 ±0.011 0.175 ±0.047 NS
NLf/Muscle weight0.33 2.189 ±0.339 3.297 ±0.807 3.472 ±0.630 NS
Deep Masseter Muscle
NLf/Jaw length 0.118 ±0.015 0.084 ±0.001 0.114 ± 0.029 NS
NLf/Muscle weight0.33 7.850 ±1.323 10.026 ±4.778 13.667 ± 3.942 NS
Whole Masseter Muscle
NLf/Jaw length 0.152 ±0.012 0.134 ±0.011 0.169 ±0.049 NS
NLf/Muscle weight0.33 1.522 ±0.228 2.564 ±0.730 2.762 ±0.530 NS
Temporalis Muscle
NLf/Jaw length 0.230 ±0.019 0.223 ±0.020 0.248 ±0.055 NS
NLf/Muscle weight0.33 1.204 ±0.149 2.365 ±0.477 2.404 ±0.510 C. apella < 0.0676
a

Results based on one-tailed Mann-Whitney U-tests. Boldfaced p-values identify significant differences following the sequential Bonferroni adjustment.

Starred (*) p-values identify significant differences prior to the sequential Bonferroni adjustment. Unstarred p-values identify differences where 0.05 < p < 0.10. NS = non-significant.

b

Results indicate direction of difference between C. apella and the untufted capuchins.

c

To maintain dimensionless ratios, we used PCSA0.5/Jaw length and NLf/Muscle weight0.333

d

Pinnation angles for the deep masseter were small and difficult to measure. We therefore treated the deep masseter as a parallel-fibered muscle and did not incorporate pinnation angle in our estimate of PCSA.