Evolution of locomotion in Anthropoidea: the semicircular canal evidence

Abstract

Our understanding of locomotor evolution in anthropoid primates has been limited to those taxa for which good postcranial fossil material and appropriate modern analogues are available. We report the results of an analysis of semicircular canal size variation in 16 fossil anthropoid species dating from the Late Eocene to the Late Miocene, and use these data to reconstruct evolutionary changes in locomotor adaptations in anthropoid primates over the last 35 Ma. Phylogenetically informed regression analyses of semicircular canal size reveal three important aspects of anthropoid locomotor evolution: (i) the earliest anthropoid primates engaged in relatively slow locomotor behaviours, suggesting that this was the basal anthropoid pattern; (ii) platyrrhines from the Miocene of South America were relatively agile compared with earlier anthropoids; and (iii) while the last common ancestor of cercopithecoids and hominoids likely was relatively slow like earlier stem catarrhines, the results suggest that the basal crown catarrhine may have been a relatively agile animal. The latter scenario would indicate that hominoids of the later Miocene secondarily derived their relatively slow locomotor repertoires.

Locomotor head movements and semicircular canal morphology in primates

“…However, body mass alone explains ∼79% of the variation in R, whereas agility explains only 0.18% of the variation in R (37). Paleontologists have used R and body mass estimates to infer the agility of movement in extinct species (2,(4)(5)(6)(7)(8)(9)(10). Because R is so much more strongly correlated with body mass than with agility, such inferences can be considered reliable only when body mass is known precisely.…”

“…Canal morphology affects endolymph flow and thus influences an animal's sensitivity to rotation; if an animal is more sensitive to rotations about some axes than others, and if different patterns of head rotation are produced by different locomotor behaviors, then canal morphology and locomotion could be functionally related. By this reasoning, differences in canal morphology in living and extinct animals have been attributed to interspecific differences in locomotion (1)(2)(3)(4)(5)(6)(7)(8)(9)(10), but characterization of any functional relationship between canal morphology and locomotion has been limited by the use of simplified models of canal sensitivity and the absence of in vivo data about how the head actually moves (11).…”

Bony labyrinth morphometry indicates locomotor adaptations in the squirrel-related clade (Rodentia, Mammalia)

“…However, with the benefits of modern non-invasive imaging techniques, such as high-resolution computed tomography (mCT), the first aspect has become a favourite topic for functional morphological analyses (e.g. [2][3][4][5][6][7][8][9][10][11][12][13]), but also for phylogenetic approaches [14 -20].…”

High morphological variation of vestibular system accompanies slow and infrequent locomotion in three-toed sloths

“…Accordingly, its bony morphology presents diverse morphological patterns correlated to the modes of locomotion and agility [1,2,[4][5][6]. A common assumption is that, notably owing to adaptive constraints, the morphology of the mammalian inner ear, especially the SC, shows low levels of intraspecific variation [7][8][9][10][11].…”