May 3, 2011

Ancient ‘Nutcracker Man’ Preferred Eating Grass

New research finds that the ancient pre-human known as "Nutcracker Man" did not dine on nuts after all, but instead dined on large quantities of grasses and sedges -- a discovery that upsets conventional wisdom about the diet of early humans.

"It most likely was eating grass, and most definitely was not cracking nuts," said University of Utah geochemist Thure Cerling, lead author of the study.

The "Nutcracker Man", or Paranthropus boisei, is an ancient human relative that roamed the African landscape more than 1 million years ago, and lived side-by-side with direct ancestors of humans, said University of Colorado-Boulder anthropology Professor Matt Sponheimer, a study co-author.

The species was given its nickname of "Nutcracker Man" due to its large, flat molar teeth and thick, powerful jaw. 

"[Paranthropus boisei]"¦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," said study co-author Kevin Uno, a University of Utah Ph.D. student in geology.

Cerling and colleagues determined the 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. 

Using a drill, Cerling pulverized some of the tooth enamel into powder.

"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 said.

"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.

The research revealed that not only did 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 percent C4 plants such as grasses, ranging from a low of 61 percent to a high of 91 percent.

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 said.

"They were competing with them."

"They were eating at the same table," he said.

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 conducted in 2008 on two teeth from "Nutcracker Man" in Tanzania also indicated the creatures ate a diet of grasses.  However, the current study, with teeth from 22 individuals, 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 larger geographic area than was known before.

"Wherever we find this creature, it is predominantly eating tropical grasses or perhaps sedges, which include papyrus," Cerling said.

Paranthropus was part of a line of close human relatives known as australopithecines, which includes the famous 3-million-year-old Ethiopian fossil Lucy, seen by some as the matriarch of modern humans.

Some 2.5 million years ago, the australopithecines are believed to have split into the genus Homo -- which produced modern Homo sapiens -- and the genus Paranthropus, which dead-ended, Sponheimer said.

"One key result is that this hominid had a diet fundamentally different from that of all living apes, and, by extension, favored very different environments," he said.

"And having a good idea of where these ancient creatures lived and what they ate helps us understand why some early hominids left descendants and others did not."

The first skull of a Paranthropus boisei individual was discovered in 1959 in Tanzania.

In 2006, a team led by Sponheimer found that a cousin of Paranthropus boisei known as Paranthropus robustus had a far more diverse diet than once believed, clouding the notion that it was driven to extinction by its finicky eating habits.  That study showed that Paranthropus robustus had a diverse diet ranging from fruits and nuts to sedges, grasses, seeds and perhaps even animals.

So what led to the end of the line for Paranthropus? It could well have been direct competition with Homo -- which was becoming skilled in extensive bone and stone technology -- or it could have been a variety of other issues, including a slower reproductive rate for Paranthropus than for Homo, Sponheimer said.

The current study was published in the May 2 online edition of the journal Proceedings of the National Academy of Sciences.

University 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 University, anthropologist Matt Sponheimer of the University of Colorado at Boulder and famed anthropologist Meave Leakey, who is affiliated with the National Museums, Stony Brook and the Turkana Basin Institute in Nairobi.


Image 1: The skull of Paranthropus boisei, known for decades as Nutcracker Man because of its large, flat teeth. Researchers from the University of Utah and other institutions are publishing a new study in which carbon isotope ratios 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. Credit: National Museums of Kenya

Image 2: 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 University 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. Credit: Melissa Lutz Blouin, University of Arkansas


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