136 CHAPTER 6 | Macroevolution and the Early Primates
Eurasia. Once joined through the region of what is now the
Middle East and Gibraltar, Old World primates, such as the
apes, could extend their range from Africa into Eurasia. Mio-
cene ape fossil remains have been found everywhere from the
caves of China, to the forests of France, to East Africa, where
scientists have recovered the oldest fossil remains of bipeds.
So varied and ubiquitous were the fossil apes of this
period that the Miocene has even been labeled by some
as the “golden age of the hominoids.” The word hominoid
comes from the Latin roots homo and homin (meaning
“human being”) and the suffix oïdes (“resembling”). As a
group, the hominoids get their name from their resem-
blance to humans.
In addition to the Old World anthropoid dental for-
mula of 2-1-2-3 and Y5 molars, hominoids can be charac-
terized by the derived characteristics of Y5 molars, having
no tail, and having broad flexible shoulder joints. As de-
scribed in Chapters 3 and 4, the likeness between humans
and the other apes bespeaks an important evolutionary re-
lationship that makes other living hominoids vulnerable
to human needs in today’s world. In the distant past, one
of the Miocene apes is the direct ancestor of the human
line. Exactly which one is a question still to be resolved.
An examination of the history of the contenders for
direct human ancestor among the Miocene apes demon-
strates how reconstruction of evolutionary relationships
draws on much more than simply bones. Scientists inter-
pret fossil finds by drawing on existing beliefs and knowl-
edge. With new discoveries, interpretations change.
The first Miocene ape fossil remains were found in
Africa in the 1930s and 1940s by the British archaeologist
A. T. Hopwood and the renowned Kenyan paleoanthro-
pologist Louis Leakey. These fossils turned up on one of the
many islands in Lake Victoria, the 27,000-square-mile lake
where Kenya, Tanzania, and Uganda meet. Impressed with
the chimplike appearance of these fossil remains, Hopwood
suggested that the new species be named Proconsul, combin-
ing the Latin root for “before” (pro) with the stage name of a
chimpanzee who was performing in London at the time.
Dated to the early Miocene 17 to 21 million years ago,
Proconsul has some of the classic hominoid features, lacking
a tail and having the characteristic pattern of Y5 grooves in
the lower molar teeth. However, the adaptations of the up-
per body seen in later apes (including humans) were absent.
These included a skeletal structure adapted for hanging sus-
pended below tree branches. In other words, Proconsul had
some apelike features as well as some features of four-footed
Old World monkeys (Figure 6.7). This mixture of ape and
monkey features makes Proconsul a contender for a miss-
ing link between monkeys and apes but not as a connection
between Miocene apes and later-appearing bipeds.
At least seven fossil hominoid groups besides Procon-
sul have been found in East Africa from the early to mid-
dle Miocene. But between 5 and 14 mya this fossil record
thins out. It is not that all the apes suddenly moved fromsize, the brain of Aegyptopithecus was smaller than that of
more recent anthropoids. Still, this primate seems to have
had a larger brain than any prosimian, past or present. Pos-
sessed of a monkeylike skull and body, and fingers and toes
capable of powerful grasping, it evidently moved about in a
quadrupedal, monkeylike manner.^13
The teeth of Aegyptopithecus suggest that this species
may be closely related to an ancestor of humans and mod-
ern apes. Although no bigger than a modern house cat,
Aegyptopithecus was nonetheless one of the larger Oligo-
cene primates. Differences between males and females in-
clude larger body size, more formidable canine teeth, and
deeper mandibles (lower jaws) in the males. In modern
anthropoids, such sexual dimorphism correlates with so-
cial systems in which competition among males is high.
New World Monkeys
The earliest evidence of primates in Central and South
America dates from this time. These fossil primates are
certainly anthropoid monkeys, with the eyes fully encased
in bone and limb bones for quadrupedal locomotion.
Scientists hypothesize that these primates came to South
America from Africa, because the earliest fossil evidence
of anthropoids is from the Old World.
Some of the African anthropoids arrived in South Amer-
ica, which at the time was not attached to any other landmass,
probably by means of floating masses of vegetation of the sort
that originate even today in the great rivers of West and Cen-
tral Africa. In the Oligocene, the distance between the two
continents was far less than it is today; favorable winds and
currents could easily have carried “floating islands” of veg-
etation to South America within a period of time that New
World monkey ancestors could have survived.^14 Nearly all
living and fossil New World primates possess the ancestral
dental formula (2-1-3-3) of prosimians compared to the de-
rived pattern (2-1-2-3) found in Old World anthropoids.
Miocene Apes
True apes first appeared in the fossil record during the
Miocene epoch, 5 to 23 mya. It was also during this time pe-
riod that the African and Eurasian landmasses made direct
contact. For most of the preceding 100 million years, the
Tethys Sea—a continuous body of water that joined what
are now the Mediterranean and Black Seas to the Indian
Ocean—created a barrier to migration between Africa and
(^13) Ankel-Simons, F., Fleagle, J. G., & Chatrath, P. S. (1998). Femoral anat-
omy of Aegyptopithecus zeuxis, an early Oligocene anthropoid. American
Journal of Physical Anthropology 106, 421–422.
(^14) Houle, A. (1999). The origin of platyrrhines: An evaluation of the Ant-
arctic scenario and the floating island model. American Journal of Physical
Anthropology 109, 554–556.