Tree shrews are small-bodied, scansorial, squirrel-like mammals that
occupy a wide range of arboreal, semi-arboreal, and forest floor niches
in Southeast Asia and adjacent islands. Comparative aspects of tree
shrew biology have been the subject of extensive investigations during
the past two decades. These studies were initiated in part because of
the widely accepted belief that tupaiids are primitive primates, and, as
such, might provide valuable insight into the evolutionary origin of
complex patterns of primate behavior, locomotion, neurobiology, and
reproduction. During the same period, there has been a renewed interest
in the methodology of phylogenetic reconstruction and in the use of data
from a variety of biological disciplines to test or formulate hypotheses
of evolutionary relationships. In particular, interest in the com-
parative and systematic biology of mammals has focused on analysis of
phy- logenetic relationships among Primates and a search for their
closest relatives. Assessment of the possible primate affinities of tree
shrews has comprised an important part of these studies, and a
considerable amount of dental, cranio- skeletal, neuroanatomical,
reproductive, developmental, and molecular evi- dence has been
marshalled to either corroborate or refute hypotheses of a special
tupaiid-primate relationship. These contrasting viewpoints have re-
sulted from differing interpretations of the basic data, as well as
alternative approaches to the evolutionary analysis of data.