Prosimians, or lower primates, tend to be insect eaters while certain types
of these primates prefer lizards or small invertebrates; monkeys—both Old
and New World—rely on fruits with a significant input from insects or small
vertebrates. Apes eat from a variety of larders (food supplies) depending
on type: orangutans eat fruit, gorillas eat stalks and pith, and chimps eat
fruit and hunt for mammals—but none eat one type to the exclusion of all
else. Physical specializations to extract nutrients from the source vary
greatly. Some primates ferment their food; others reingest it.
The shape of teeth and jaws, and the length of gut and digestive tract,
also affect different emphases of diet. Fruit eaters, for example, are
equipped with molars that are not shaped for crushing or grinding, but are
small in relation to their body size (Kay, 2005). Some leaf eaters, like
colobines or howler monkeys, have sacculated stomachs containing
bacteria that aid in digestion. One type of lemur is probably
coprophagous; that is, like rabbits, it ingests its own waste pellets to
extract semidigested nutrients. The length of the gut in primates that eat
any kind of animal is 4 to 6 times its body length, while that of a leaf eater
is 10 to 30 times its body length (Milton, 1993).
Primates, unlike some other mammals, require certain vitamins. The most
important substances, vitamins B12 and C, must be obtained from outside
sources. In the case of B12, it must be extracted from animals including
insects (Wakayama, Dillwith, Howard, & Blomquist, 1984), and for vitamin
C, from fruits and a little from muscle meat. Genes controlling the
manufacture of these substances were reassigned (exapted), as it were,
to other functions when the anthropoid group of monkeys, apes, and
humans split from prosimians. The genetic information is affirmed by the
fact that some prosimian relatives of the earliest primates are still able to
synthesize these substances (Milton, 1993).
