The functional morphology of caudal vertebrae in new world monkeys

Abstract

New World monkeys vary considerably in the manner and degree to which they use their tails. There ought to arise a corresponding variation in the stresses on caudal vertebrae. Consequently, different behavior types will have contrasting caudal morphologies. This study investigates caudal morphology of several New World monkeys representing the large range of ability from totally nonprehensile tails to the dexterous fifth limb of spider monkeys. One large-bodied, nonprehensile-tailed Old World monkey is included to offset the correlation between size and degree of prehensility in New World monkeys. These monkeys vary both within and between species as to the number of caudal vertebrae and the length of individual vertebrae. Despite this variation, the length of caudal vertebrae within a given tail decreases at a constant rate across species. The width of the vertebrae at two points, midbone and the proximal end, separates the monkeys with prehensile tails from those with nonprehensile tails. The middle of the vertebrae is wider and more robust in prehensile-tailed forms. This is associated with stronger bones in tails subject to greater stress. THe proximal width of each bone is also greater in the prehensile-tailed monkeys. This measure reflects the lateral development of the proximal transverse process. This provides a larger lever arm for M. caudalis lateralis, implying greater rotational ability.

The Late Permian herbivore Suminia and the early evolution of arboreality in terrestrial vertebrate ecosystems

“…Among anomodonts, these features are seen only in Suminia. These characteristics indicate a relative expansion of the anterior region of the tail and are probably related to a hypertrophy of the musculoskeletal system along the proximal part of the tail in order to enable balancing and potentially prehensile abilities in this small synapsid (German 1982;Jenkins & Krause 1983;Rose 1987;Youlatos 2003). (Arnold 1998), pterosaurs (Clark et al 1998) and birds (Hopson 2001).…”

“…Hopson 2001;Bloch & Boyer 2002;Luo et al 2003). While prehensile tails are characterized by a number of characteristics (German 1982;Youlatos 2003), autopodial specializations are expressed in either one or two digits being markedly divergent from the remaining digits in the manus and pes. Such a pattern is well known in extant primates and other placental mammals, as well as marsupials, chameleons, certain tree frogs and perching birds (Cartmill 1985;Hildebrand & Goslow 2001).…”

The Tail of Tyrannosaurus: Reassessing the Size and Locomotive Importance of the M. caudofemoralis in Non‐Avian Theropods

“…The associations between muscle mass, vertebrae morphology, and function have been well studied in the tails of extant mammals, particularly procyonids and primates, and tail biomechanics are better understood among mammals than any other group of terrestrial vertebrates (Dor, 1937;German, 1982;Lemelin, 1995;Organ et al, 2009). However, in terms of mass and volume, most fully terrestrial mammals have unimpressive tails.…”

Muscular anatomy of the tail of the western grey kangaroo, Macropus fuliginosus

“…The distal caudal vertebrae have no zygapophyses, though they retain mammillary processes and transverse processes (German 1982). Observations of articulated skeletons of M. fuliginosus suggest that caudal vertebrae 11-13 are likely to contact the ground during pentapedal locomotion.…”