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

^aResults 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.

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

^cTo maintain dimensionless ratios, we used PCSA^0.5/Jaw length and NLf/Muscle weight^0.333

^dPinnation 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.