|Arm bone fragments from a 1.34-million-year-old hominin, Paranthropus boisei, were discovered by an international research team, including a CU Denver anthropologist, in Tanzania. (Credit: University of Colorado Denver)|
While P. boisei was known for its massive jaws and cranium -- anthropologist Mary Leakey discovered the first skull in 1959 in northern Tanzania -- the build and skeletal adaptations of the rest of the archaic hominin's body have been unknown until recently.
During excavations at Olduvai in 2010-2011, the team discovered the partial skeleton of a large adult individual who is represented by various teeth and skeletal parts. Other team members are Manuel Dominguez-Rodrigo, Ph.D., professor of anthropology and prehistory at Complutense University, Madrid; Audax Mabulla, Ph.D., associate professor of archaeology, University of Dar es Salaam, Tanzania, Gail Ashley, Ph.D., professor of geological sciences, Rutgers University; David Uribelarrea, Ph.D. a professor of geology at Complutense University of Madrid; Henry Bunn, Ph.D., professor of anthropology, University of Wisconsin-Madison; and Travis Pickering, Ph.D., professor of anthropology, University of Wisconsin-Madison.
P. boisei was a long-lived species of archaic hominin that first evolved in East Africa about 2.3 million years ago. In the absence of evidence of other skeletal remains, it was commonly assumed that the skeleton of P. boisei was like that of more ancient species of the genus Australopithecus, from which P. boisei likely evolved.
"We are starting to understand the physiology of these individuals of this particular species and how it actually adapted to the kind of habitat it lived in," Musiba said. "We knew about the kind of food it ate -- it was omnivorous, leaning more toward plant material -- but now we know more: how it walked around and now we know it was a tree climber."
The size of the arm bones suggests strong forearms and a powerful upper body. "It's a different branch on our ancestry tree," Musiba said. "It came later than the other hominins, so the question now is 'what happened to it?' We're going to do more work on biomechanics and see what else this creature was doing."
He noted that the creature likely stood 3.5 to 4.5 [4.5 to 5.5] feet tall and possessed a robust frame. "We know that it was very strong," Musiba said. "It's unprecedented to find how strong this individual was. The stronger you are the more adaptive you are."
In summer 2014, the bones will be displayed as part of a large exhibit on human origins in Dar es Salaam, Tanzania. The joint-museum exhibit involves the Museum of Human Evolution in Burgos, Spain, the Regional Museum of Archaeology in Madrid, and the National Museum of Dar es Salaam.
With each find scientists are adding to the understanding of how humans evolved and adapted to their surroundings through time. "The more we are finding of these fossils, the more we are learning about the history of these species," Musiba said.
|Older version of skeleton. From Richard Leakey, Origins|
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No Nuts for 'Nutcracker Man': Early Human Relative Apparently Chewed Grass Instead
Study co-author Kevin Uno, a University of Utah Ph.D. 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 Australopithecus.
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.
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 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 says.
"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 in Tanzania 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 on diets.
"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 stage.
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 and Ethiopia) 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.