title: Does cortical bone thickness in the last sacral vertebra differ among tail types in primates?
abstract: The external morphology of the sacrum is demonstrably informative regarding tail type (i.e., tail presence/absence, length, and prehensility) in living and extinct primates. However, little research has focused on the relationship between tail type and internal sacral morphology, a potentially important source of functional information when fossil sacra are incomplete. Here, we determine if cortical bone cross-sectional thickness of the last sacral vertebral body differs among tail types in extant primates and can be used to reconstruct tail types in extinct primates.
  
  
  
  Cortical bone cross-sectional thickness in the last sacral vertebral body was measured from high-resolution CT scans belonging to 20 extant primate species (N = 72) assigned to tail type categories ("tailless," "nonprehensile short-tailed," "nonprehensile long-tailed," and "prehensile-tailed"). The extant dataset was then used to reconstruct the tail types for four extinct primate species.
  
  
  
  Tailless primates had significantly thinner cortical bone than tail-bearing primates. Nonprehensile short-tailed primates had significantly thinner cortical bone than nonprehensile long-tailed primates. Cortical bone cross-sectional thickness did not distinguish between prehensile-tailed and nonprehensile long-tailed taxa. Results are strongly influenced by phylogeny. Corroborating previous studies, Epipliopithecus vindobonensis was reconstructed as tailless, Archaeolemur edwardsi as long-tailed, Megaladapis grandidieri as nonprehensile short-tailed, and Palaeopropithecus kelyus as nonprehensile short-tailed or tailless.
  
  
  
  Results indicate that, in the context of phylogenetic clade, measures of cortical bone cross-sectional thickness can be used to allocate extinct primate species to tail type categories.
authors.affiliation: Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University, Stony Brook, New York, 11794.
authors.forename: Abigail C
authors.initials: AC
authors.lastname: Nishimura
authors.affiliation: Department of Anthropology, Stony Brook University, Stony Brook, New York, 11794.
authors.forename: Gabrielle A
authors.initials: GA
authors.lastname: Russo
mesh_terms: D000818:Animals; D000071538:Cortical Bone / Q000033:anatomy & histology* / Q000502:physiology; D005260:Female; D008297:Male; D011323:Primates / Q000033:anatomy & histology* / Q000502:physiology*; D012447:Sacrum / Q000033:anatomy & histology* / Q000502:physiology; D013045:Species Specificity; D013623:Tail / Q000033:anatomy & histology* / Q000502:physiology
keywords: functional morphology; sacrum; tail function; tail length; vertebral column