I find that fieldwork in almost any locale quickly settles down into a
daily routine. The work itself is often repetitive, even though the scientific
results can vary dramatically from day to day. Our days in the bottom
of the ravine by the Yellow River consist mostly of reducing large blocks
of fossil-bearing rock to smaller ones, a process that is randomly punctuated
by Wen’s standard victory call—“You yige ya-chuang! You yige
ya-chuang!” (I’ve got a jaw!)—whenever he finds something he thinks
is interesting. Wen himself is particularly fond of large fossils, possibly
because of his culture’s long-standing fascination with “dragon bones.”
Usually, I know that Wen’s most agitated cries mean that he has stumbled
across the limb bones or jaws of the hippolike animal known as Anthracokeryx,
the most common large mammal found at this locality. But
Wen appreciates that the rest of us become more excited by relatively
complete specimens of smaller mammals.
Today, Wen is in particularly fine form, whacking away at the freshwater
limestone with gusto. It is May 21, 1995, and Wen knows that the
field season is scheduled to end within the week, so that our team can
return to Beijing in time to plan the logistics of future research before
the American members have to catch their return flights home. The end
of the field season means big changes in all of our daily lives. Most of us
will return to our academic lifestyles, writing grant proposals and technical
articles, preparing lectures, and attending administrative meetings.
Wen will go back to being a farmer in the village of Zhaili. Maybe it’s
the thought of the upcoming changes that spurs Wen onward. In any case,
he seems determined to find something important today. Looking back
on it now, I doubt that Wen could possibly have dreamed of making such
a momentous discovery as he hoisted his pick once more.
I can still hear the distinct thump of Wen’s rock pick striking that fateful
blow. Immediately, Wen’s excited chatter makes me drop whatever
I’m working on to see what all the fuss is about. Wen shouts: “Yige xiao
ya-chuang, heng piao-liang! Ni kan-kan!” (A small jaw—very beautiful.
You must see it for yourself!). As soon as I see what Wen’s hefty pick has
revealed, my heart begins to race. A large block of freshwater limestone

Figure 2. The author and Wen Chaohua at Locality 1 in the
Yuanqu Basin of central China, where Mr. Wen discovered
the complete lower dentition of Eosimias centennicus in
1995.

I find that fieldwork in almost any locale quickly settles down into a
daily routine. The work itself is often repetitive, even though the scientific
results can vary dramatically from day to day. Our days in the bottom
of the ravine by the Yellow River consist mostly of reducing large blocks
of fossil-bearing rock to smaller ones, a process that is randomly punctuated
by Wen’s standard victory call—“You yige ya-chuang! You yige
ya-chuang!” (I’ve got a jaw!)—whenever he finds something he thinks
is interesting. Wen himself is particularly fond of large fossils, possibly
because of his culture’s long-standing fascination with “dragon bones.”
Usually, I know that Wen’s most agitated cries mean that he has stumbled
across the limb bones or jaws of the hippolike animal known as Anthracokeryx,
the most common large mammal found at this locality. But
Wen appreciates that the rest of us become more excited by relatively
complete specimens of smaller mammals.

Today, Wen is in particularly fine form, whacking away at the freshwater
limestone with gusto. It is May 21, 1995, and Wen knows that the
field season is scheduled to end within the week, so that our team can
return to Beijing in time to plan the logistics of future research before
the American members have to catch their return flights home. The end
of the field season means big changes in all of our daily lives. Most of us
will return to our academic lifestyles, writing grant proposals and technical
articles, preparing lectures, and attending administrative meetings.
Wen will go back to being a farmer in the village of Zhaili. Maybe it’s
the thought of the upcoming changes that spurs Wen onward. In any case,
he seems determined to find something important today. Looking back
on it now, I doubt that Wen could possibly have dreamed of making such
a momentous discovery as he hoisted his pick once more.

The American members of the team include both paleontologists and
geologists. Mary Dawson, my colleague at the Carnegie Museum of Natural
History, specializes in the early evolution of rodents, rabbits, and
their kin. Her role in the discovery of the first Eocene vertebrates north
of the Arctic Circle, on Ellesmere Island in the Canadian Arctic archipelago,
has won her widespread acclaim. John Kappelman, an anthropologist
from the University of Texas, is a leading expert on the later phases
of higher primate evolution, especially the evolution of apes during the
Miocene Epoch. John’s role in our expedition relates to his other professional
hat, that of paleomagnetic stratigrapher. Together with Wulf
Gose, a geologist from the University of Texas, and Tim Ryan, his graduate
student, Kappelman hopes to determine the age of the fossils we
find, using the episodic reversals in the Earth’s magnetic field as a guide.
Wen Chaohua, a peasant farmer from the neighboring village of Zhaili,
rounds out our field crew. I first met Mr. Wen the previous year, when
we hired him as a manual laborer. Slight of build but surprisingly strong,
Wen rapidly earned a spot on our team because of his solid work habits,
his quick smile, and his unbridled enthusiasm for finding fossils. Though
Wen has only the minimal educational background typical of rural Chinese
of his generation, he shows plenty of raw intelligence. Had he been
fortunate enough to grow up under different circumstances, I’m sure Wen
could have been successful in almost any endeavor he chose to pursue.
This year, Wen looks positively professorial wearing his new eyeglasses,
which correct a minor astigmatism that had bothered him last year. Like
me, Wen sports a small hand lens tied around his neck, which he uses to
examine small fossils up close. In recognition of his hard work, Mary
Dawson gave Wen her own hand lens at the conclusion of our previous
field season. Now that he has the standard tools of the trade, Wen takes
even greater pride in his work. Our reward is a steady stream of fossils.
Wen’s role on our field crew is simply to extract large blocks of fossilbearing
rock from the bottom of the ravine. Other members of the team
then break each block down more finely in search of any fossils that might
lie inside. Wen’s tool of choice for this enterprise is a large, steel rock
pick hafted onto a stout wooden handle. This Wen wields with all of the
exuberance of a forty-niner searching for a vein of gold. Invariably, Wen

himself uncovers many fossils, simply because he exposes so much fresh
fossil-bearing rock with each powerful swing of his pick. At first, it was
hard to restrain Wen from attempting to extricate the fossils he encountered
during his daily assault on the layers of limestone and mudstone.
Now, with a field season of experience under his belt, Wen understands
that whenever he happens across a fossil, he must stop his work and alert
the rest of the team.

bottom of the ravine on the northern bank of the Yellow River seems like
a promising place to start.
To search for such elusive fossils, a highly interdisciplinary and international
team of scientists has converged on this remote corner of central
China. Each member brings a unique set of skills and knowledge to
the table. On the Chinese side are four scientists from the Institute of
Vertebrate Paleontology and Paleoanthropology (or IVPP), a branch of
the Chinese Academy of Sciences. Tong Yongsheng, a veteran of numerous
field campaigns all over the People’s Republic, originally hails from
Zhejiang Province, along China’s southern coastline. A muscular man
of medium build, Tong specializes in small mammals from the Eocene,
especially rodents and insectivores (shrews, hedgehogs, and the like).
Wang Jingwen, who grew up in Beijing, primarily studies ungulates, or
hooved mammals, from the Eocene. Lately, though, Wang has developed
an abiding interest in early primates, which allows the two of us to collaborate
closely on joint research projects. Huang Xueshi boasts the most
eclectic interests of any member of our team, having worked on fossils
ranging in age from Paleocene to Oligocene. Huang’s excellent mastery
of English, combined with his strong local dialect, makes him the object

of the occasional joke. Other Chinese sometimes ask him to speak to them
in English so that they can better understand him! Guo Jianwei, the
youngest Chinese member of the team, focuses on the evolution of ruminant
artiodactyls—the large group of even-toed ungulates that includes
living deer, giraffes, antelopes, goats, and cattle.

 

 Despite unanimous scientific agreement that humans share a close
common ancestry with monkeys and apes, one of the most controversial
issues in paleoanthropology today is how, when, and where the first
anthropoids—the common ancestors of monkeys, apes, and people—
evolved. In stark contrast to the relatively abundant fossil record for early
humans, the fossil record for anthropoid origins is spotty, incomplete,
and seemingly incoherent. Paleontology, like other branches of science,
abhors such a vacuum. The main purpose of our expedition is to help
flesh out this distant phase of our evolutionary history. Yet the simple
fact that our team is searching for fossils of early anthropoid primates
in Eocene rocks in central China is, in several respects, unorthodox—if
not downright heretical.
Our goal is to test a bold new hypothesis about anthropoid origins—
one that moves the birthplace of these remote human ancestors from
Africa to Asia while it ruptures the established evolutionary timetable by
tens of millions of years. This sweeping idea rests on the wobbly foundation
provided by some fragmentary fossils from another Chinese site
known as Shanghuang that I had recently named Eosimias (“dawn monkey”
in Latin and Greek). If we are to have any hope of gaining scientific
traction, we must find better fossils of Eosimias and animals like it. The

Figure 1. Major differences in cranial anatomy distinguish prosimians from anthropoids.
Illustrated here (from left to right) are skulls of a ruffed lemur (Varecia variegata), a South
American squirrel monkey (Saimiri sciureus), and a human (Homo sapiens). Note the basic
similarity in skull form in the two anthropoids, which differ from the lemur in having a relatively
larger brain, a reduced snout, fused mandibular symphysis and metopic suture, and
a complete postorbital septum. Original art by Mark Klingler, copyright Carnegie Museum
of Natural History.

Monkeys, apes, and humans are collectively known as anthropoids or
“higher primates.” Compared to prosimians, living anthropoids possess

larger brains, eye sockets that are almost completely surrounded by bone,
a single lower jaw bone (or mandible) formed by the fusion of two separate
bones at the chin, and many other anatomically advanced features.
In terms of their behavior, anthropoids again differ from most prosimians,
although there is some overlap between species of each group. In
general, anthropoids tend to live in complex groups characterized by intricate
social interactions among individual members. Some prosimian
species, in contrast, live quite solitary lives. All anthropoids aside from
the South American owl monkey (Aotus) are diurnal—that is, they are
mainly active during daytime. Many prosimians, notably tarsiers, bushbabies,
lorises, and some lemurs, strongly prefer to move about and feed
at night. These profound differences between prosimians and anthropoids
extend to the molecular level. Analyses of long sequences of the DNA of
various species of monkeys, apes and humans show that all of these species
are far more similar to one another than any of them are to prosimians.
In an evolutionary context, this means that, whether we analyze anatomy,
behavior, or DNA, the conclusion remains inescapable. We humans are
much more closely related to monkeys and apes than we are to lemurs
or tarsiers. Put slightly differently, monkeys share a more recent common
ancestor with us than they do with prosimians.

In terms of its prevailing climate, the Eocene was virtually a mirror
image of the Pleistocene or “Ice Ages,” when much of human evolution
transpired. It began with a pronounced episode of global warming some
fifty-five million years ago. Such optimal conditions allowed tropical and
subtropical forests—and the animals that inhabit them—to occur at much
higher latitudes than they do today. Because primates have always prospered
in these warm forest habitats, the Eocene was truly a heyday for
primate evolution. Among their other accomplishments, Eocene primates
extended their geographic range far beyond its current limits. Fossils of
Eocene primates have been found as far north as Saskatchewan in North
America, England and Germany in Europe, and Mongolia in Asia. As I
discuss in greater detail in subsequent chapters, the fossil record shows
that during the Eocene, even these northern continental regions supported
diverse evolutionary radiations of primates. After enduring for more than
twenty million years, the greenhouse world of the Eocene ended thirtyfour
million years ago, when the Earth’s climate once again became cooler
and drier. It is unlikely to be a coincidence that this severe climatic deterioration
witnessed the extinction of primates in North America and
Europe, where tropical and subtropical habitats disappeared.
The vast majority of the fossil primates known from the Eocene resemble
the most primitive primates alive today. These animals, collectively
known as prosimians, include the diverse radiation of lemurs native
to Madagascar, the bushbabies of continental Africa, the lorises of
Africa and southern Asia, and, perhaps strangest of all, the tarsiers of
Southeast Asian islands. Prosimians resemble other primates, including
humans, in possessing nails rather than claws on most digits of their hands
and feet, and in having eyes that face forward to allow for enhanced,
“stereoscopic” vision. Like all primates aside from humans, prosimians
have a grasping big toe, functionally akin to the human thumb. Yet
prosimians also differ from humans and our nearest primate relatives,
the monkeys and apes, in many aspects of their anatomy, physiology, and
behavior.