Eric Sargis (Ph.D. Anthropology, City University of New York)  is conducting research on the evolutionary relationships of the mammalian order Primates, the order to which humans belong. In an attempt to determine which group of mammals represents the closest primate relative, examination of a non-primate mammalian species, such as the tree shrew (order Scandentia), is necessary. The Pen-Tailed tree shrew (shown here) is of particular importance because it may represent a living ecological model of the ancestral primate. Initial high resolution 3-D digitizing of the skeletons of tree shrews, primates, and other mammals has revealed a similarity between tree shrews and early fossil primates.

Photograph by Larry Burrows, Life Magazine © 1965, Time Inc. In: Martin, R.D. (1982) Et tu, tree shrew? Natural History (August): 26-33. 

Further reading:

1996  Szalay F.S. & Lucas S.G.  The postcranial morphology of Paleocene Chriacus and Mixodectes and the phylogenetic relationships of archontan mammals.  Bull. New Mex. Mus. Nat. Hist. Sci. 7: 1-47.