This photo of casts of two palates demonstrates the large size of the teeth of Paranthropus boisei (left), an early human relative that lived in East Africa between 2.3 million and 1.2 million years ago and was known as Nutcracker Man. Much smaller teeth from a human skull are shown on the right. A new study led by Univ. of Utah researchers shows that Nutcracker Man didn’t eat nuts as had been believed for decades, but instead used the large, flat teeth to chew grasses or plants known as sedges. Photo: Melissa Lutz Blouin, Univ. of Arkansas
For decades, a 2.3 million- to 1.2
million-year-old human relative named Paranthropus boisei has been
nicknamed Nutcracker Man because of his big, flat molar teeth and thick,
powerful jaw. But a definitive new Univ.
of Utah study shows that
Nutcracker Man didn’t eat nuts, but instead chewed grasses and possibly sedges—a
discovery that upsets conventional wisdom about early humanity’s diet.
“It most likely was eating grass, and most
definitely was not cracking nuts,” says geochemist Thure Cerling, lead
author of the study published in an online edition of the Proceedings of
the National Academy of Sciences.
Study co-author Kevin Uno, a Univ. of Utah PhD
student in geology, adds: “This study provides evidence that Paranthropus
boisei was not cracking nuts, but was instead eating mainly tropical
grasses or sedges. It was not competing for food with most other primates, who
ate fruits, leaves, and nuts; but with grazers—zebras’ ancestors, suids
[ancestors of pigs and warthogs], and hippos.”
Cerling and colleagues determined the extinct,
upright-walking Paranthropus boisei‘s diet by analyzing carbon isotope
ratios in the tooth enamel of 24 teeth from 22 individuals who lived between
1.4 million and 1.9 million years ago and were closely related to and once
thought part of the genus of human ancestors named Australopithecus.
Both extinct Paranthropus and the human genus Homo arose from
Univ. of Utah researchers Cerling and Uno
conducted the study with three scientists from the National Museums of Kenya—anthropologist
Emma Mbua and paleontologists Francis Kirera and Fredrick Manthi—and with
Frederick Grine of Stony Brook Univ., anthropologist Matt Sponheimer of the Univ.
of Colorado at Boulder and famed anthropologist Meave Leakey, who is affiliated
with the National Museums, Stony Brook and the Turkana Basin Institute in
Drilling for evidence of prehistoric dinners
Cerling used a drill to pulverize some tooth enamel into powder, but only 2
milligrams per tooth and only from the broken surface of broken teeth, leaving
the original surfaces intact for future study. Still, there was anticipation
among officials at the National Museums of Kenya, where the teeth are housed.
“The sound of the drill may make a lot of
paleontologists and museum staff cringe, but as the results of this study show,
it provides new information that we can’t get at any other way,” Uno says.
“And we’ve gotten very good at drilling.”
Carbon isotope ratios in tooth enamel can reveal
whether ancient animals ate plants that used what is called C3 photosynthesis—trees
(and the leaves, nuts, and fruits they produce), shrubs, cool-season grasses,
herbs, and forbs—or plants such as warm-season or tropical grasses and sedges
that use what is known as C4 photosynthesis. (Sedges vaguely resemble grasses,
but their stems’ cross-sections usually are triangular, which means
“sedges have edges” when rotated between thumb and finger.)
The study found that not only did the Nutcracker
Man Paranthropus boisei not eat nuts or other C3 plant products, but
dined more heavily on C4 plants like grasses than any other early human, human
ancestor, or human relative studied to date. Only an extinct species of
grass-eating baboon had a diet so dominated by C4 plants.
Carbon isotopes showed the 22 individuals had
diets averaging 77% C4 plants such as grasses, ranging from a low of 61% to a
high of 91%.
That’s statistically indistinguishable from grass
diets of grazing animals that lived at the same time: the ancestors of zebras,
pigs and warthogs, and hippos, Cerling says.
The skull of Paranthropus boisei, known for decades as Nutcracker Man because of its large, flat teeth. Researchers from the Univ. of Utah and other institutions are publishing a new study in which carbon isotope ration in tooth enamel reveal that the early human relatives, which went extinct, likely used its big teeth and powerful jaw to chew grasses, but didn’t eat nuts. Photo: National Museums of Kenya
“They were competing with them,” he
adds. “They were eating at the same table.”
The researchers also analyzed oxygen isotope
composition in the fossil teeth, which indicated Paranthropus boisei
lived in semi-arid savannah with woodlands along rivers or lakes.
Research in 2008 on two teeth from Nutcracker Man
also indicated the creatures ate a diet of grasses and perhaps sedges. But with
teeth from 22 individuals, the new study shows the species was eating grass and
other C4 plants over a much longer time period (from 1.4 million to 1.9 million
years ago) and bigger geographic area (a 500-mile-wide swath of East Africa)
than was known before.
“Wherever we find this creature, it is
predominantly eating tropical grasses or perhaps sedges, which include
papyrus,” Cerling says.
Rethinking the diets of early human
ancestors and relatives
The new study of Nutcracker Man may provoke a major change in how we view the
diets of other early humans and human relatives.
“Much of the previous work has been on the
size and shape of the teeth, along with microwear analysis,” Cerling says.
“Our results [on Paranthropus boisei] are completely different
than the conclusions based on 50-plus years of research along those lines. It
stands to reason that other conclusions about other species also will require
revision. P. boisei greatly extends the range of potential diets for
early human lineages.”
Specifically, scientists have believed human
ancestors in the genus Australopithecus—which gave rise to now-extinct
Paranthropus and to Homo or early humans—also had head and
tooth features suggesting they ate hard objects like nuts.
Cerling says carbon isotope ratios in
australopiths’ teeth now should be studied, since the Paranthropus findings
bring in to question interpretations that are made without isotopic information
“The high proportion of C4 vegetation in the
diet of Paranthropus boisei makes it different from any other hominin
to date, even its closest relative, Paranthropus robustus from
southern Africa,” Uno says. “The
results make an excellent case for isotope analysis of teeth from other members
of our family tree, especially from East Africa.”
A brief biography of ‘Nutcracker Man’
The cranium of the extinct early human relative now known as Paranthropus
boisei was discovered by Meave Leakey’s in-laws, Mary and Louis Leakey, in
1959 at Olduvai Gorge in Tanzania, and helped put the Leakeys on the world
Dated at 1.75 million years old, it initially was
known as Zinjanthropus boisei (zinj for an African religion named
Zanj, anthropus for ape-human and boisei after expedition benefactor Charles
Boise) and later as Australopithecus boisei, before scientists decided
it deserved a separate genus, making it Paranthropus boisei.
The discovery of other P. boisei fossils
revealed the species lived in East Africa (including Kenya
from 2.3 million years ago to 1.2 million years ago. The short creatures had
big, flat premolars and molars; thick tooth enamel; muscle-attachment surfaces
for large chewing muscles; and powerful jaws. Those characteristics earned Paranthropus
boisei the nickname Nutcracker Man—a name that has been attributed to
South African paleoanthropologist Phillip Tobias, a colleague of the Leakeys.
According to Dale Peterson’s biography of
anthropologist Jane Goodall, the Leakeys took privately to calling the Zinj
skull “Dear Boy,” and that it was Tobias who convinced them to switch
the genus to Australopithecus and who also suggested that the thick
molars made the skull look like a children’s wooden toy named Nutcracker Man.
“So while the rather obscure and academic
debates about naming and grouping the skull kept all the specialists
entertained, for the public at large, this same fossil became simply Nutcracker
Man,” Peterson wrote.
“Nutcracker Man never has been used in the scientific literature, but
that’s the common name,” Cerling says.