• New World monkeys, such as the marmosets, spider monkeys, and howler monkeys

The origin and evolution of primates
The overall evolutionary pattern of primates remains un-
settled (see figure 10.5), although the origin of the order has
recently been estimated at close to 85 million years rather
than the 65 million that has generally been assumed. Some
kind (or kinds) of species ancestral to all primates survived
the mass extinction 65 million years ago that spelled the end
of the Age of Reptiles, with the dinosaurs being the most
notorious of the extinctions. Soon into the subsequent Age of
Mammals, “primates of modern aspect” appeared approx-
imately 50 million years ago, beginning an adaptive radiation
that included an increase in range of body size and a con-
comitant broadening of diet. The 200 modern species repres-
(a)
Lemurs and lorises
Tarsiers
Anthropoids
Omomyid
group
Adapid
group
(b)
Lemurs and lorises
Tarsiers
Anthropoids
Omomyid
group
Adapid
group
?
(c)
Lemurs and lorises
Tarsiers
Anthropoids
Omomyid
group
Adapid
group
“Third
group”?
Figure 10.5 Three views of primate evolution: A good deal 
of uncertainty exists over the pattern of primate evolution. Until
recently most opinion was divided between schemes (a) and (b),
which show differences over the origin of anthropoids. A third view
(c) has also been proposed, which postulates a third, early group of
primates that was ancestral to modern anthropoids. Based on the
most recently discovered fossil evidence, however, scheme (a) is
now most strongly supported.

---

adapid specimen was found early in the nineteenth century.
Although these two large and geographically widely dis-
persed families now seem well accepted as the earliest
known primates, the question of their origin persists, if they
are not derived from the plesiadapiforms.
One of the most spectacular discoveries, announced in 1994,
included five new types of early primate, of both omomyid
and adapid affinities, at the Shanhuang site in southeastern
China. The diversity of species at this site exceeds that found
in all of the rest of Asia and in well-documented sites in
Europe and North America. One of the most interesting finds
involved teeth that are virtually identical to those of modern
tarsiers. Huxley speculated that the anatomical range of the
lower-to-higher primates in today’s world gives a window
into the group’s evolutionary history. The Chinese find indeed
implies the modern tarsier might be a “living fossil.” (Not lit-
erally, of course, but the group simply has not changed much
since its origin.) (See figure 10.6.)
Uncertainty has long swirled around the evolutionary root
of the suborder Anthropoidea (monkeys, apes, and humans).
Some anthropologists have argued that its origin lies within
the adapids; others have favored the omomyids. Both
schemes put the origin of anthropoids close to 35 million
years ago. A recently developed argument suggests that 
neither group is ancestral to anthropoids, but that a third
group existed. Algeripithecus minutus, discovered in Algeria
and reported in May 1992, is suggested to be a specimen of
the latter group. The Shanhuang fossils provide support for
the omomyid affinity with anthropoids, however. The dental
formula of one specimen, Eosimias, is what would be expected
of an ancestral anthropoid (hence its name). Eosimias is more
closely linked to omomyids than to adapids, thus forging a
link with the ancestral tarsier group. It now seems likely that
modern tarsiers and modern anthropoids shared a specific
common ancestor. If correct, this pattern of primate evolu-
tion would put the origin of anthropoids closer to 50 million
years ago rather than the 35 million years that was previously
believed.
of which was Purgatorius, which was found a century ago in
Montana and later at several other sites. The plesiadapiforms
constituted a successful group living in the Paleocene and
early Eocene (55 to 65 million years ago) of North America
and Europe, amounting to some 25 genera and 75 species.
The range of body size was considerable, stretching from 20
grams to more than 3 kilograms. Most members of the group
were probably insectivores. Their supposed phylogenetic link
with later primates is somewhat limited, resting on the 
primatelike structure of the cheek teeth and ear structure. In
other respects the plesiadapiforms are somewhat specialized,
including the possession of large anterior teeth and three or
fewer premolars (many of the earliest prosimians have four
premolars). For these reasons, the plesiadapiforms were
probably not ancestral to prosimians, but possibly formed a
sister group in the primate clade. Some researchers contend,
however, that the plesiadapiforms were not primates at all,
but instead are linked with the modern colugo (also mislead-
ingly called flying lemurs).
The 1990s witnessed a flurry of discoveries related to early
primates. These advances are helping to resolve the early his-
tory of the group, extend its known geographic range, and
root its origins and diversification deeper in the past, perhaps
even before the end-Cretaceous extinction.
For instance, in 1990, French researchers announced the
discovery in Morocco of a collection of 10 undoubtedly prim-
ate cheek teeth, which were described as a new species,
Altiatlasius koulchii. The species, which is estimated to have
weighed less than 100 grams, is thought to belong to the 
family Omomyidae, one of two major groups of early, true
primates. A North American discovery, consisting of a rela-
tively rare cache of fossil skulls, is also said to be an omomyid,
of the species Shoshonius cooperi, which lived a little more
than 50 million years ago. The omomyidsatiny, nocturnal,
fruit-eating speciesaare considered to be ancestral to tarsiers.
The second major group of early primates, the Adapidaea
diurnal folivores, frugivores, and insectivoresawere larger
than omomyids and are putative ancestors of lemurs. An
10: Primate Heritage