Allometry and Interspecific Differences in the Facial Cranium of Two Closely Related Macaque Species

Tsuyoshi Ito,Masanaru Takai,Takeshi Nishimura

doi:10.1155/2011/849751

Abstract

Interpreting evolutionary history of macaque monkeys from fossil evidence is difficult, because their evolutionary fluctuations in body size might have removed or formed important morphological features differently in each lineage. We employed geometric morphometrics to explore allometric trajectories of craniofacial shape in two closely related species, Macaca fascicularis and M. fuscata. These two species exhibit a single shared allometric trajectory in superoinferior deflection of the anterior face, indicating that the differences in this feature can be explained by size variation. In contrast, two parallel trajectories are demonstrated in craniofacial protrusion, indicating that even if they are comparable in size, M. fuscata has a higher and shorter face than M. fascicularis. The degree of facial protrusion is most likely a critical feature for phyletic evaluation in the fascicularis group. Such analyses in various macaques would help to resolve controversies regarding phyletic interpretations of fossil macaques.

Highlights

Macaques are medium-sized cercopithecine monkeys, which are currently distributed widely in the southern, southeastern, and eastern regions of Asia, and in a restricted area of northern Africa [1]
PC1 is inversely correlated with the centroid size for all the samples of the two species (R2 = 0.42, P < .001); M. fascicularis samples have significantly higher PC1 score than M. fuscata samples (t = 26.8, P < .001; Figure 2(a))
PC2 is significantly correlated with the centroid size separately for each species, M. fascicularis (R2 = 0.46, P < .001) and M. fuscata (R2 = 0.43, P < .001; Figure 2(b)), while M. fascicularis has significantly higher PC2 scores than M. fuscata (t = 8.06, P < .001; Figure 2(b))

Summary

Introduction

Macaques are medium-sized cercopithecine monkeys, which are currently distributed widely in the southern, southeastern, and eastern regions of Asia, and in a restricted area of northern Africa [1]. Evolutionary and dispersal histories of the fascicularis group have been proposed based on their morphological variations, fossil records [7, 9], and evidence of the mitochondrial and Y-chromosome genes [10,11,12]. According to their studies, ancestral M. fascicularis might have originated in the equatorial region [7, 9] and subsequently dispersed to the islands on the Sunda Shelf during periods of marine regression due to glacio-eustasy and northward to the mainland of Southeast Asia [7, 9]. The current distribution has been formed by intricate dispersal events of the four species with the recent speciation during the Pleistocene period, during which at least six major glacial episodes occurred with significant climate fluctuations [6, 13]

Methods

Results

Discussion

Conclusion