The prehensile tail, one capable of suspending the entire body weight of the animal, evolved independently at least 14 times among 40 genera in 14 mammalian families. This includes the independent (and parallel) evolution of tail prehensility in the platyrrhine subfamily Atelinae (Alouatta, Ateles, Brachyteles, Lagothrix) and in the genus Cebus, as well as the independent evolution in a single genus (Potos) of the Carnivoran family Procyonidae. The numerous instances of prehensile tail evolution in arboreal mammalian taxa suggest that such an adaptation provides an effective locomotor strategy for negotiating arboreal habitats. Yet, despite its importance for balance, feeding behavior, and locomotion, little is known about the structural properties of the prehensile tail, and how these differ in the nonprehensile tail.

The mechanical loading that a prehensile tail incurs during suspension suggests that prehensile tail vertebrae should be structured to resist higher bending/torsional moments than nonprehensile tail vertebrae. Similarly, prehensile tail musculature should be structured to generate higher forces than nonprehensile tail musculature. Furthermore, previous research suggests that the disparities in vertebral and muscle structure should become more drastic further distally within the tail. To test these predictions, this study evaluated caudal vertebral cross-sectional geometry, as well as muscle fiber architecture of lateral flexor caudal musculature at three specific tail locations in prehensile- and nonprehensile-tailed platyrrhines and procyonids. Confirming predictions, caudal vertebrae of prehensile-tailed taxa exhibited increased resistance to bending/torsion in each region of the tail compared to nonprehensile tail vertebrae, and the disparities between tail types became more drastic further distally within the vertebral sequence. Likewise, structure of lateral flexor caudal musculature (mm. intertransversarii caudae) varied between prehensile and nonprehensile tails, where prehensile tail muscles were capable of generating higher forces than their nonprehensile tail homologues.

Prehensile-tailed platyrrhines and procyonids exhibited similar patterns in vertebral structure, but comparisons of muscle structure were hampered by small sample sizes. Nevertheless, the presence of similar tail vertebral morphologies in prehensile-tailed taxa from different mammalian Orders demonstrates multiple solutions to the problem of locomoting through Neotropical forests. The fact that these morphologies are quite similar across these different taxonomic groups is remarkable indeed.