Thought to have used tools—and possibly fire—the creature is the oldest named species in the human genus, Homo, study author Darren Curnoe says.
The new-species designation is based on two-million- to 800,000-year-old fossil-skull pieces, jaws, teeth, and other bones found at the Sterkfontein caves complex in South Africa's Gauteng Province.
Though only fragmentary fossils from about six individuals have been found, upright-walking H. gautengensis is thought to have stood a squat three and a half feet (one meter) tall and weighed about 110 pounds (50 kilograms), according to Curnoe, an anthropologist at the University of New South Wales, Australia.
Compared with modern humans, the new species had proportionally long arms, a projecting face somewhat like a chimp's, larger teeth, and a smaller brain—though not too small for verbal communication.
"While it seems possible that Homo gautengensis had language," Curnoe said via email, "it would have been much more rudimentary than ours, lacking the complex tones and lacking a grammar, as all human languages have."
Human But Not Habilis?
Though it's said to be the oldest named human species, H. gautengensis, or "Gauteng man," appears too late in the evolutionary time line to be our direct ancestor, Curnoe believes.
"Large-bodied hominins like Homo erectus, which are likely to be our ancestors, have been found dating to the same period as [some] Homo gautengensis"—which suggests H. erectus's predecessor arose earlier than H. gautengensis, he said. Hominins, or hominids, are humans plus human ancestral species and their close evolutionary relatives.
Furthermore, Curnoe noted, human fossils some 300,000 years older than H. gautengensis have been found in East Africa and have yet to be classified. (Explore a prehistoric time line.)
"I think, in all honesty," he said, "we don't yet know which species was our earliest direct ancestor in the human evolutionary line."
Even though H. gautengensis isn't likely in our direct lineage,
the potential new species had humanlike characteristics, according to Curnoe.
The anthropologist said he's detected 40 features that appear to separate the bipedal creature from the more apelike human ancestors called australopithecines. The traits include "a much smaller face, with narrow teeth, and much smaller chewing muscles and jaws, compared to the australopithecines," he said.
For decades scientists—including Curnoe—have assigned the fossils now marked H. gautengensis to Homo habilis ("handy man"). Believed to have arisen between 2 million and 1.5 million years ago, H. habilis is widely considered the oldest named human species.
But, he said, "after 14 years of work on the South African Homo record, I decided that there was a strong case for recognizing and naming a new species"—one separate from, and older than, H. habilis.
For one thing, H. gautengensis individuals have smaller brains—perhaps only a third the size of our own. The new species also has smaller teeth and jaws than H. habilis, which may indicate a different diet and lifestyle, Curnoe said.
H. Gautengensis a Sometime Swinger?
While H. gautengensis likely lived mainly on the ground, there's evidence the human ancestor spent some time in the trees, Curnoe said.
Fossil traces of "inner-ear organs of balance suggest that there may have been a mixture of lifestyles," with "some individuals engaging in regular arboreal behavior and others perhaps much more terrestrial," Curnoe said.
Today it isn't unusual for gorillas and forest baboons to show such behavior, with females typically climbing trees more than males, the anthropologist noted.
Tools ... and a Touch of Cannibalism?
The H. gautengensis fossils were found alongside basic stone tools and evidence of the use of fire. The most complete human ancestor skull from the sediments associated with H. gautengensis is a widely studied mid-1970s discovery labeled Stw 53.
The stone tools would have been used for "'de-fleshing' and cutting open bones to access marrow, and probably also for digging and [preparing] plant foods," he said. "They might also have been used for processing animal hides."
Cut marks on the Stw 53 skull hint at darker practices—"that it was de-fleshed, either for ritual burial or cannibalistic consumption."
Along with the burned bones of a prehuman of the genus Paranthropus found in the same cave, the marks suggest that "hominin was certainly on the menu of Homo gautengensis," Curnoe added.
But H. gautengensis wasn't exclusively carnivorous. The new species had teeth apparently adapted for eating plant material that looks to have required plenty of chewing, according to the study, soon to be published in the human-biology journal HOMO.
New "Missing Link" Broken Already?
The new species hails from a region called the Cradle of Humankind, which also produced the recently announced Australopithecus sediba, said to be the "key transitional species" between the apelike australopithecines and the first human species.
But the new study casts doubt on those findings, Curnoe said.
The newfound Australopithecus—with its tiny brain and long, apelike arms and wrists adapted to life in trees—"is much more primitive than Homo gautengensis" yet they both "lived at the same time and in the same place," he said.
Assuming A. sediba co-existed with the new early human species, then A. sediba is "less likely to be the ancestor of humans" than its proponents say it is—it's simply too late in the fossil record‚ Curnoe argued.
Unruly Evolutionary Tree
Paleontologist Fred Spoor of the Max Planck Institute for Evolutionary Anthropology in Germany agrees that H. gautengensis and A. sediba appear to contradict each other.
In fact, he noted, the A. sediba team had argued that Stw 53 is a more primitive skull than that of A. sediba. In other words, H. gautengensis may not be human at all but an apelike australopithecine.
Spoor, who wasn't involved in either study, said experts have puzzled over Stw 53 for years.
For one thing, "there is not enough bone preserved to make an uncontroversial reconstruction" of the skull, Spoor said.
Furthermore, South African fossil hominins are much harder to date than those from East Africa, "where you have all these beautiful volcanic ash layers which you can date."
The "bizarre specimen" doesn't fit in with other known hominin skulls and may well signal a new species, he said—"a lot of people have suggested it." But whether that new species is human or australopithecine will continue to be debated.
Study author Curnoe, for his part, said, "The real significance of the new species is that it shows just how complicated, how bushy, our evolutionary tree was.
"There were many different species living at the same time, and alongside our own species and ancestors, until really very recently."
As for the fate of H. gautengensis, he said, "It is up to my colleagues to decide whether they are convinced that a new species is warranted and whether they will use [the designation] in their research.
"Ultimately, history will decide."
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