Posts tagged Professor Matt Sponheimer
The males of two bipedal hominid species that roamed the South African savannah more than a million years ago were stay-at-home kind of guys when compared to the gadabout gals, says a new high-tech study led by the University of Colorado Boulder.
The team, which studied teeth from a group of extinct Australopithecus africanus and Paranthropus robustus individuals from two adjacent cave systems in South Africa, found more than half of the female teeth were from outside the local area, said CU-Boulder adjunct professor and lead study author Sandi Copeland. In contrast, only about 10 percent of the male hominid teeth were from elsewhere, suggesting they likely grew up and died in the same area.
“One of our goals was to try to find something out about early hominid landscape use,” said Copeland, who also is affiliated with the Max Plank Institute for Evolutionary Anthropology in Leipzig, Germany. “Here we have the first direct glimpse of the geographic movements of early hominids, and it appears the females preferentially moved away from their residential groups.”
A paper on the subject is being published in the June 2 issue of Nature. Co-authors included CU-Boulder anthropology Professor Matt Sponheimer, Darryl de Ruiter from Texas A&M University, Julia Lee Thorp from the University of Oxford, Daryl Codron from the University of Zurich, Petrus le Roux from the University of Cape Town, Vaughan Grimes of Memorial University-St. John’s campus in Newfoundland and Michael Richards of the University of British Columbia in Vancouver.
The new study results were somewhat surprising, said Copeland. “We assumed more of the hominids would be from non-local areas, since it is generally thought the evolution of bipedalism was due in part to allow individuals to range longer distances,” she said. “Such small home ranges could imply that bipedalism evolved for other reasons.”
The team used a high-tech analysis known as laser ablation, zapping the hominid teeth with lasers to help them measure isotope ratios of strontium found in tooth enamel in order to identify specific areas of landscape use. A naturally occurring element, strontium is found in rocks and soils and is absorbed by plants and animals.
Since unique strontium signals are tied to specific geological substrates — like granite, basalt, quartzite, sandstone and others — they can be used to reveal landscape conditions where ancient hominids grew up, said Copeland. “The strontium isotope ratios are a direct reflection of the foods these hominids ate, which in turn are a reflection of the local geology.”
The study was funded by the National Science Foundation, the Max Planck Society, a University of Colorado LEAP Associate Professor Growth Grant and the University of Colorado Dean’s Fund for Excellence.
“It is difficult enough to work out relations between the sexes today, so the challenges in investigating the ways that male and female hominids used the landscape and formed social groups over a million years ago are considerable, to say the least,” said CU-Boulder’s Sponheimer. “Disembodied skulls and teeth are notoriously poor communicators, so the real difficulty with a study like this is finding new ways to make these old bones speak.”
Strontium isotope signatures are locked into the molars of mammals by the end of tooth enamel formation — for the hominids, probably at about eight or nine years old when they were traveling with their mothers. The Sterkfontein and Swartkans cave systems that yielded the teeth are less than a mile apart and dominated by a sedimentary carbonate rock known as dolomite, which has a distinct strontium signal, she said.
The team tested 19 teeth dating from roughly 2.7 to 1.7 million years ago from both Australopithecus africanus and Paranthropus robustus individuals from the two caves, which are well known for yielding valuable scientific data on hominid evolution.
Because the male hominids, like male humans, were larger than the females, the team used the size of individual molars to determine which were most likely from males or females, said Copeland. They also compared them to teeth and jaw fossils recovered from five early hominid sites in South Africa.
Both Paranthropus robustus and Australopithecus africanus were part of a line of close human relatives known as australopithecines that included the Ethiopian fossil, Lucy, estimated to be some 3.2 million years old and regarded by many as the matriarch of modern humans. While Australopithecus africanus may be a direct ancestor of modern humans, Paranthropus robustus and its close relative, Paranthropus boisei, both dead-ended on a side branch of the hominid family tree for reasons still unknown.
The female dispersal pattern believed seen in the two hominid groups is similar to that of many modern humans, chimpanzees and bonobos, said Copeland. But it is a dispersal pattern unlike most other primates — including gorillas — where the females stay with the group they are born into and the males move elsewhere. “This study gets us closer to understanding the social structure of ancient hominids, since we now have a better idea about the dispersal patterns,” she said.
The team also used laser ablation to zap 38 fossilized teeth of baboons, antelope, and small, rodent-like creatures known as hyraxes that lived in the same area at about the same time as the two australopithecine species under study. The results showed nearly all of the mammal teeth were local, implying such groups had relatively small home ranges, much like the australopithecine males, said Copeland.
While Sponheimer said the study could be taken as support for the position that bipedalism arose for reasons other than improved locomotion, the data might also indicate that many hominids simply preferred to live on dolomite substrates where caves would have been abundant. “I’ve never thought of these early male hominids as the quintessential cavemen, but the potential use of caves at this early time period is something worth considering.”
In addition, the team analyzed more than 170 modern plants and animals within a 30- mile-radius the two cave systems, sampling 11 different geological substrates. The minimum distance from the cave systems to non-local geology areas is about two miles to the southeast, four miles to the northwest, and more than 20 miles each in northeast and southwest directions, said Copeland. It is still not clear where the roaming female australopithecines identified in the study spent their formative years, she said.
An ancient, bipedal hominid sporting a set of powerful jaws and huge molars that earned it the nickname “Nutcracker Man” likely didn’t crack nuts at all, preferring instead to slurp up vast quantities of grasses and sedges, says a new study.
The hominid, known as Paranthropus boisei, ranged across 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. It was long assumed Paranthropus boisei favored nuts, seeds and hard fruit because of its huge jaws, powerful jaw muscles and the biggest and flattest molars of any known hominid in the anthropological record, he said.
In the last several years, research on the wear marks of teeth from Paranthropus boisei by other research teams has indicated it likely was eating items like soft fruit and grasses, said Sponheimer. That evidence, combined with the new study that measured the carbon isotopes embedded in fossil teeth to infer diet, indicates the rugged jaw and large, flat tooth structure may have been just the ticket for Paranthropus boisei to mow down and swallow huge amounts of grasses or sedges at a single sitting, he said.
“Frankly, we didn’t expect to find the primate equivalent of a cow dangling from a remote twig of our family tree,” said Sponheimer.
Published in the May 2 issue of the Proceedings of the National Academy of Sciences, the study was led by University of Utah Professor Thure Cerling. Other authors included Emma Mbua, Frances Kirera, Fredrick Manthi and Meave Leakey from the National Museums of Kenya, Fredrick Grine from Stony Brook University in New York and Kevin Uno from the University of Utah.
“Fortunately for us, the work of several research groups over the last several years has begun to soften prevailing notions of early hominid diets,” said Sponheimer. “If we had presented our new results at a scientific meeting 20 years ago, we would have been laughed out of the room.”
For the new study, the researchers removed tiny amounts of enamel from 22 Paranthropus boisei teeth collected in central and northern Kenya, each of which contained carbon isotopes absorbed from the types of food eaten during the lifetime of each individual. In tropical environments, virtually all trees and bushes — including fruits and leaves — use the so-called C3 photosynthetic pathway to convert sunlight into energy, while savannah grasses and some sedges use the C4 photosynthetic pathway.
The isotope analysis indicated Paranthropus boisei individuals were much bigger fans of C4 grasses and sedges than C3 trees, shrubs and bushes. The results indicated the collective diet of the 22 individuals averaged about 77 percent grasses and sedges for a period lasting at least 500,000 years, said Sponheimer.
The research team also compared the carbon isotope ratios of Paranthropus teeth with the teeth of other grazing mammals living at the same time and in the same area, including ancestral zebras, hippos, warthogs and pigs. The results indicated those mammals were eating primarily C4 grasses, virtually identical to Paranthropus boisei. “They were eating at the same table,” said Cerling.
Paranthropus was part of a line of close human relatives known as australopithecines that includes the famous 3-million-year-old Ethiopian fossil Lucy, seen by some as the matriarch of modern humans. Roughly 2.5 million years ago, the australopithecines are thought to have split into the genus Homo — which produced modern Homo sapiens — and the genus Paranthropus, that dead-ended, said Sponheimer.
“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 by co-author Meave Leakey’s in-laws, Mary and Louis Leaky, 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 picky eating habits. Published in Science magazine, the 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, he said.
The new study was funded by the National Science Foundation and the CU-Boulder Dean’s Fund for Excellence.