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.

MISSING LINKS AND DAWN MONKEYS

What is unique about this particular ravine, though, is not the loess.
In this part of Shanxi Province, loess is ubiquitous, draping over older
geological features like autumn leaves covering a well-kept lawn. But here,
as the ravine approaches the Yellow River, it cuts deep into the loess. For
the last fifty yards or so of its existence, the ravine finally succeeds in
breaking through the loess altogether to expose the much older underlying
strata. Even to the untrained eye, it is clear that these rocks are different,
both in terms of their composition and their segregation into different
layers or beds. They consist of alternating bands of blue-green
mudstone, pale yellow and white limestone, and thick gray sandstones,
the last of which show internal evidence of stratification in the form of
minute swales of sand grains known as cross-bedding. The fossils we seek
are concentrated in the layers of mudstone and limestone. They are
roughly forty million years old, about six times older than the earliest
putative hominids ever discovered. They pertain to an interval of Earth
history known as the Eocene, the Greek roots of which translate more
or less as “dawn of recent [life].”
As its etymology suggests, the Eocene was a pivotal period in the history
of life on Earth—a time of transition from ancient to modern. The
earliest members of most living orders of mammals first appeared and
became geographically widespread, replacing more archaic forms that
left no living descendants. Such distinctive and highly specialized types
of modern mammals as bats and whales first showed up in the Eocene,
together with the earliest odd-toed ungulates (horses, rhinos, and tapirs),
even-toed ungulates (pigs, camels, and primitive relatives of deer and antelopes),
and others. The order of mammals to which we belong, the Primates,
also first became geographically widespread and ecologically
prominent at the beginning of the Eocene, although a few scattered fossils
hint that primates are somewhat older yet. At the same time, the
Eocene witnessed the decline and extinction of many groups of mam-

mals that first evolved alongside the dinosaurs, or immediately following
their demise. Examples include the vaguely rodentlike multituberculates,
the raccoon- or bearlike arctocyonids, and the large herbivores
known as pantodonts and uintatheres. The Eocene also witnessed a great
evolutionary diversification of flowering plants, together with the insects
that feed on them.3

MISSING LINKS AND DAWN MONKEYS

To the north and east, wheat fields extend across the plateau as far as
the eye can see. Immediately west of the ravine, the sleepy village of Zhaili
shelters the peasant farmers who tend the surrounding fields. A narrow
path, hewn into the western wall of the ravine, provides access to the
bottom some 150 feet below for the villagers and their sheep and goats.
Walking down this path, you can’t help but notice the peculiar nature of
the nearly vertical walls of the ravine. The rock defining both sides of
the ravine is soft and pliable, so easy to work that many people in this
part of China actually carve small caves into it, which function as storage
rooms or even small homes. Geologically, this type of rock is known
as loess. It is composed of wind-blown sediment laid down by countless
dust storms that swept across this part of China during the Pleistocene
Epoch, when vast ice sheets were expanding and contracting farther north
in Siberia.

MISSING LINKS AND DAWN MONKEYS

A fuller consideration of human origins requires us to place our own
evolutionary history within a broader context. Did humans take longer
to evolve our unique characteristics than other living primates, or did
our ancestors simply experience unusually high rates of evolution? For
that matter, how unique are humans with respect to other primates anyway?
Which seemingly “human” traits are ours alone, and which are
shared with various primate relatives? Where do humans lie on the family
tree of all primates, and what does that tree look like? Where do primates
lie on the larger family tree of all mammals? Were there particularly
critical events during the earlier phases of our evolutionary history,
before our own lineage branched away from those leading to chimpanzees
and other living primates? Today, these questions pose far greater scientific
challenges than simply filling in the constantly shrinking gaps in
the human fossil record. Yet, ironically, when most people hear the term
“missing link,” they think of a gap in the fossil record that supposedly
fails to link modern humans with our apelike ancestors. The dirty little
secret of paleoanthropology is that, while there are plenty of missing links,
they don’t occur where most people think they do. They exist farther
back in deep time. Ultimately, this is why I’m at the bottom of a ravine
on the banks of the Yellow River.
The ravine itself is a natural erosional feature, an ephemeral drainage
flowing into the Yellow River from the north. It dissects a relatively flat
plateau, which—like most rural parts of central China—is now under intensive
wheat cultivation. Standing on top of the plateau at the head of
the ravine offers a panoramic view of the surrounding terrain. To the
south, on the far side of the Yellow River in Henan Province, lie rugged
mountains composed primarily of limestone of Ordovician age. Some 450
million years ago—about twice the age of the earliest known dinosaurs—
the rock now forming the crest of this range was deposited in a warm,
shallow sea not unlike that surrounding the modern Bahamas.

MISSING LINKS AND DAWN MONKEYS

Paleoanthropology is the scientific study of human origins. In the
strictest sense, paleoanthropologists seek to illuminate the evolutionary
history of the human lineage as it evolved from our more apelike ancestors.
Fossil hominids are the crown jewels of paleoanthropology. Without
them, theories about when, where, and how our species evolved
would be helter-skelter, unconstrained by hard data. One of the great triumphs
of twentieth century science has been the recovery of an amazing
diversity of hominid fossils, mainly from eastern and southern Africa,
but also from various parts of Eurasia, ranging from France and Spain
to China and Indonesia. Discoveries of new fossil hominids continue unabated.
Considered as a whole, the fossil record of early humans is now

complete enough that, at least in broad strokes, we know how humans
evolved from more apelike precursors. Virtually all paleoanthropologists
agree, for example, that the human lineage originated sometime between
five and seven million years ago in Africa, and that early humans acquired
the ability to walk upright on two legs millions of years before their brains
enlarged much beyond those of chimpanzees.2

MISSING LINKS AND DAWN MONKEYS

My persistence is rewarded when I split apart another block of greenish-gray limestone. Inside I find a nearly complete maxilla, or upper jaw, of a small rodent, replete with three black teeth that glisten like fresh obsidian in the sunlight. Peering through a hand lens that I keep tied to a leather thong draped like a necklace under my tee shirt, the diagnostic pattern of cusps and crests on the fossilized teeth readily identifies the creature as Pappocricetodon schaubi. A primitive progenitor of modern mice, rats, and gerbils, Pappocricetodon is the most abundant fossil mammal known from this site.1 Though it’s not exactly the pivotal discovery I had hoped for, finding the mortal remains of any animal that lived millions of years ago invigorates the mind. I begin to contemplate the weighty scientific issues that have led me to travel halfway around the world, to this remote part of central China’s Shanxi Province.

My particular area of scientific expertise, vertebrate paleontology, is
in the midst of a sea change. Much of what I learned as a graduate student
is being challenged by provocative new fossils and new methods of
interpreting them, if not discarded altogether. Increasing globalization
and the collapse of the Soviet Union and its satellite states have opened
up most of the world to paleontological exploration, including places
that, only a few years earlier, I never dreamed of being able to visit in
search of fossils. On a separate front, molecular biologists are sequencing
the DNA of various organisms at an increasingly frenetic pace, churning
out megabytes of raw data that are being used to test old ideas, and
to propose new ones, about the evolutionary relationships of living plants
and animals. All in all, it feels like a unique moment in history and a
great time to be a paleontologist, especially when you’re involved in one
of the most exciting debates to hit the field of paleoanthropology in many
years.

Missing Links and Dawn Monkeys

Missing Links and Dawn Monkeys

In rural China, the highest compliment you can get is not that you’re
attractive or smart. It’s that you work really hard. As I shift to stay in
the scant midday shade offered by a deep ravine on the northern bank
of the Yellow River, this proletarian attitude makes a lot of sense. When
I left the United States earlier this month, spring had barely begun. Checking
the calendar in my field notebook, I see that it’s only mid May—too
early in the season for a heat wave. Yet for the past few days, my team
has endured triple digit temperatures. Each of us sports a tan several
shades deeper than our normal hue. A few yards away, where he chips
at a piece of freshwater limestone that just might contain a fossil, my
colleague Wang Jingwen is beginning to live up to his nickname, which
translates roughly as “black donkey.” I’m told that the local villagers have
been praising our work ethic, because when it gets this hot, even the peasants
take a siesta under a shade tree.
We have no choice but to tolerate the heat of the noon sun, because
it provides the best lighting conditions for finding fossils. At this time of
day, there are no shadows to hide the small jaws and limb bones that
have been entombed in these rock strata for the past forty thousand millennia
or so. Having traversed twelve time zones to get here, I’m not about
to forgo the chance to find an important specimen merely because of the

oppressive heat.

adopt a monkey for free

Missing Links and Dawn Monkeys