Title Tail length estimation from sacro-caudal skeletal morphology in catarrhines

Tail morphology in primates is important for interpreting functional adaptation and phylogeny. Tail length is probably the most remarkable trait. Establishing usable methods to predict the tail length of extinct primates is a part of the basis to reconstruct primate evolution, particularly of hominoids. Previous studies revealed that sacral morphology often predicts tail length. However, most of the previous studies have only attempted this by using categories (e.g., short, long, etc.). A problem in those studies is that the range of intermediate tail length is wide (whose tail length is 15.0 through100 percent of head to body length (15.0 < RTL < 100.0 %)). Accordingly, this study aimed to quantitatively estimate tail length in catarrhines with intermediate tail lengths. Sacral and proximal caudal vertebral (first to third) of 89 hybrid individuals between Japanese macaque (Macaca fuscata) and Formosan rock macaque (Macaca cyclopis) were measured. Fifteen regression formulae were produced to estimate tail length in these species. These hybrid macaques were phylogenetically controlled but varied greatly in their relative tail length (tail length / head and body length = 18.8 88.8%), and thus were an excellent sample to obtain general regression formulae to estimate catarrhine tail length. A total of 15 predicting models were devised and five formulae performed well. The utility of these formulae were confirmed by an application to 15 species/subspecies of catarrhine taxa.