Abstract
Macaques (genus Macaca) are known to have wide variation in tail length. Within each species group tail length varies, which could be associated with a phylogenetic trend seen in caudal vertebral morphology. We compared numbers and lengths of caudal vertebrae in species of the fascicularis group, M. assamensis (sinica group), M. nemestrina (silenus group), and those obtained from reports for an additional 11 species. Our results suggest different trends in number and lengths. The caudal vertebral length profiles revealed upward convex patterns for macaques with relative tail lengths of ≥15%, and flat to decreasing for those with relative tail lengths of ≤12%. They varied between species groups in terms of the lengths of proximal vertebrae, position and length of the longest vertebra, numbers and lengths of distal vertebrae, and total number of vertebrae. In silenus and sinica group, the vertebral length is the major skeletal determinant of tail length. On the other hand, the vertebral number is the skeletal determinant of tail length in the fascicularis group. Tail length variation among species groups are caused by different mechanisms which reflect the evolutionary history of macaques.
Highlights
The macaques are known for its great variation of tail length[1,2,3,4,5,6,7]
Since the function differs in caudal vertebrae, such as proximal vertebrae are acting as the foundation for movement and distal vertebrae are responsible for balancing mechanism by its weight, the comparison of number and length in different vertebrae are essential information to consider macaques’ tail evolution and adaptation
We obtained measurements of the caudal vertebrae from skeletal specimens stored at the Kyoto University Primate Research Institute (KUPRI) and the Japan Monkey Centre (JMC), selecting only adults based on their complete epiphyseal fusion
Summary
The macaques (genus Macaca) are known for its great variation of tail length[1,2,3,4,5,6,7]. Most of the changes occurred in Old World primates and the genus Macaca was the notably high in changes, those were four increases and three decreases[29] They mentioned that the tail increase were seen in three clades separately; (a) M. nemestrina, M. silenus, M. pagensis, and M. leonine; (b) M. sinica, M. radiata, and M. munzala; (c) M. cyclopis, M. mulatta, and M. fascicularis[29], which exactly follows the species group; (a) silenus group, (b) sinica group, and (c) fascicularis group. From these studies we hypothesize there could be species groups’ trend in number and length of caudal vertebrae. The caudal vertebral number and length could have phylogenetic trends and/or characteristics dependent on tail length
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