Mj. Ravosa et Cf. Ross, CRANIODENTAL ALLOMETRY AND HETEROCHRONY IN 2 HOWLER MONKEYS - ALOUATTA-SENICULUS AND A-PALLIATA, American journal of primatology, 33(4), 1994, pp. 277-299
Cranial dimensions were collected from growth series for two sexually
dimorphic congeners: Alouatta seniculus, the red howler monkey, and Al
ouatta palliata, the mantled howler monkey. In both A. seniculus and A
. palliata, ontogenetic series for males and females were compared to
evaluate if sexual dimorphism in skull form results from the different
ial extension of common patterns of relative growth. Subsequently, gro
wth series for both species were compared to investigate whether morph
ological differences between species also result from the ontogenetic
scaling of cranial proportions. Analyses indicate that cranial proport
ions for both sexes of Alouatta palliata are ontogenetically scaled. I
n mantled howlers, males apparently reach larger terminal size by grow
ing for a longer duration and, to a lesser extent, at a faster rate th
an females. Data for both sexes of Alouatta seniculus indicate that cr
anial proportions are also ontogenetically scaled. In particular, male
red howlers apparently reach larger adult size by growing at a faster
rate and, perhaps, to an equivalent or longer duration than females.
The Alouatta seniculus data underscore apparent differences in the rat
e and timing components of sex dimorphism, possibly due to sexual diff
erences among dental eruption patterns, cranial development, somatic g
rowth, and socioecological factors. Results for both species indicate
that intrasexual selection for size differentiation has a minimal effe
ct on brain size and postcanine tooth size dimorphism. Lastly, compari
sons of allometric trajectories for both species further demonstrate a
strong pattern of ontogenetic scaling of cranial proportions. (C) 199
4 Wiley-Liss, Inc.