134 CHAPTER 6 | Macroevolution and the Early Primates
recently, the earliest evidence consisted of the tiny species
Eosimias (pronounced “ee-o-sim-ee-us”; Latin for “dawn
of the monkeys”), represented by fossils from China,
dated to about 45 mya. The Chinese fossils represent
several species of tiny, insect-eating animals and are the
smallest primates ever documented.^6 Some scientists have
challenged whether these tiny fossils are truly anthropoids
as they are reconstructed largely from foot bones rather
than skulls or teeth. As described in the chapter opener, in
2009, controversy and media attention swirled around the
spectacularly well-preserved 47-million-year-old potential
anthropoid nicknamed “Ida.” 7,8,9,10 Initially discovered thirty
years ago through a mining and drilling operation at an old
quarry near the southern German hamlet of Messel, Ida’s
remains were separated and sold to different collections. In
Ida’s time, the Messel region was a tropical forest with a lake
and volcano. Fossils from this region are embedded into
flaky layers of rock that split open into “plates.” Now that the
two plates that constitute Ida have been reunited, scientists
can debate whether Ida is indeed the earliest anthropoid
or not. This distinction, which would place her on the line
leading to humans, captures our imaginations as described
in this chapter’s Biocultural Connection by anthropologist-
primatologist Meredith Small.
More recent than Ida and well into the Oligocene epoch,
rich deposits of primate fossils have been found in Fayum,
Egypt. These fossils include a diverse range of species in-
cluding some of the earliest to possess a dental comb. But
more relevant to human ancestry are the early anthropoid
primate species from Fayum, identified through dental,
cranial, and postcranial (the rest of the skeleton) remains.
Some possess the ancestral dental formula (2-1-3-3) seen in
New World monkeys and prosimians, while others have the
derived dental formula shared by Old World monkeys and
apes: two incisors, a canine, two premolars, and three mo-
lars on each side of the jaw. The eye orbits have a complete
wall, the latter being a feature of anthropoid primates.^11
Although there is still much to be learned about the Eo-
cene primates, it is clear that they were abundant, diverse,
and widespread. Among them were ancestors of today’s
prosimians and anthropoids.^12 With the end of the Eocene,
substantial changes took place among the primates, as
among other mammals. In North America, now well iso-
lated from Eurasia, primates became extinct, and elsewhere
their range seems to have been reduced considerably.
Climate change affected primate and mammalian evo-
lution. Through the late Eocene, climates were becoming
somewhat cooler and drier, but then temperatures took a
sudden dive, triggering the formation of an ice cap over
previously forested Antarctica. The result was a marked
reduction in the range of suitable environments for pri-
mates. At the same time, cold climate led to lower sea lev-
els through the formation of ice caps, perhaps changing
opportunities for migration of primates.Oligocene Anthropoids
During the Oligocene epoch, from about 23 to 34 mya, the
anthropoid primates diversified and expanded their range.
Fossil evidence from Egypt’s Fayum region has yielded suf-
ficient fossils (more than 1,000) to reveal that by 33 mya,
Old World anthropoid primates existed in considerable di-
versity. Moreover, the cast of characters is growing, as new
fossils continue to be found in the Fayum, as well as in newly
discovered localities in Algeria (North Africa) and Oman
(Arabian Peninsula). At present, we have evidence of at least
sixty genera included in two families. During the Oligocene,
prosimian fossil forms became far less prominent than an-
thropoids. Only on the large island of Madagascar (off the
coast of East Africa), which was devoid of anthropoids until
humans arrived, is prosimian diversity still evident. In their
isolation, they underwent a further adaptive radiation.
Fossil evidence indicates that these Old World anthro-
poids were quadrupeds who were diurnal, as evidenced by
their smaller orbits (eyes). Many of these Oligocene species
possess a mixture of monkey and ape features. Of particular
interest is the genus Aegyptopithecus (pronounced “Egypt-
o-pith-ee-kus”; Greek for “Egyptian ape”), an Oligocene an-
thropoid that has sometimes been called a monkey with an
ape’s teeth. Aegyptopithecus possessed a mosaic of monkey
and ape features as well as features shared by both groups.
Its lower molars have the five cusps of an ape, and the upper
canine and lower first premolar exhibit the sort of shearing
surfaces found in monkeys and apes. Its skull has eye sock-
ets that are in a forward position and completely protected
by a bony wall, as is typical of modern monkeys and apes.
The endocast of its skull indicates that it had a larger visual
cortex than that found in prosimians. Relative to its body(^6) Gebo, D. L., et al. (2001). Middle Eocene primate tarsals from China: Im-
plications for haplorhine evolution. American Journal of Physical Anthro-
pology 116, 83–107.
(^7) Franzen, J. L., et al. (2009). Complete primate skeleton from the middle
Eocene of Messel in Germany: Morphology and paleobiology. PLoS ONE 4
(5), e5723.
(^8) Dalton, R. (2009). Fossil primate challenges Ida’s place: Controversial
German specimen is related to lemurs, not humans, analysis of an
Egyptian find suggests. Published online 21 October 2009, Nature 461 ,
1040, doi:10.1038/4611040a; Editorial. Media frenzy. Nature 459 , 484,
doi:10.1038/459484a; Published online 27 May 2009.
(^9) Simons, E. L., et al. (2009). Outrage at high price paid for a fossil. Correspon-
dence Nature 460 , 456, doi:10.1038/460456a; Published online 22 July 2009.
(^10) Seiffert, E. R., et al. (2009). Convergent evolution of anthropoid-like adap-
tations in Eocene adapiform primates. Nature 461 , 1118–1121, doi:10.1038/
nature08429; Received 11 July 2009; Accepted 18 August 2009.
(^11) Simons, E. L. (1995). Skulls and anterior teeth of Catopithecus (Primates: An-
thropoidea) from the Eocene and anthropoid origins. Science 268, 1885–1888.
(^12) Kay, R. F., Ross, C., & Williams, B. A. (1997). Anthropoid origins. Science
275 , 803–804.