Smithsonian.com

An artist's conception of the unusual humans living in southwestern China 11,500 to 14,300 years ago. Image © Peter Schouten

Last week, an international group of researchers reported the discovery of fossils belonging to a strange population of hominids that lived in southwestern China as recently as 11,500 years ago, at the end of the Pleistocene Epoch. The fossils resemble modern humans in many ways but possess some unusual characteristics. The traits may be evidence that Homo sapiens were more diverse in the past—or a sign that scientists have uncovered a new species.

Anthropologist Darren Curnoe of the University of New South Wales in Australia led the analysis of the fossils, detailed in the journal PLoS ONE. The bones—a partial skull, skull cap, jaws and teeth—came from Longlin Cave in Guangxi Province and Malu Cave in Yunnan Province, and date to  11,500 to 14,300 years ago. In comparing the Chinese bones with those of recent humans, H. sapiens living during the Pleistocene, Neanderthals and Homo erectus, the researchers concluded the Chinese fossils have a unique mix of modern features and traits rarely, if ever, seen in recent and Pleistocene humans, such as a very broad face and a protruding jaw.

The most dramatic interpretation of the fossils is that they represent a newly discovered species that lived alongside modern humans in East Asia until very recently. Anthropologist Chris Stringer of the Natural History Museum in London thinks that’s a feasible idea. In fact, the fossils could be the remains of the mysterious Denisovans, Stringer told New Scientist. Scientists discovered the Denisovans a few years ago while analyzing DNA recovered from a finger bone found in a Siberian cave that dated to 30,000 to 48,oo0 years ago. The DNA didn’t align with that of modern humans or Neanderthals, the only species known to inhabit the area at the time. Since then, scientists have been looking to match a face to the DNA. This idea will be confirmed only if the researchers manage to retrieve DNA from any of the Chinese fossils.

A less headline-worthy explanation is that these hominids were members of an early, unknown migration of H. sapiens out of Africa. (Genetic evidence indicates there were at least two migrations into Eurasia: one at 60,000 to 70,000 years ago and another at 30,000 to 40,000 years ago.) Once these people settled in East Asia, they somehow remained isolated from other human populations for thousands of years and eventually died out without leaving behind descendants. Under this scenario, the population’s unusual features suggest our species was more diverse thousands of years ago than it is today. This possibility is supported by other fossils found in Africa. Curnoe and his colleagues describe H. sapiens fossils found in East, South and North Africa, dating from 12,000 to 100,000 years ago, that possess a mix of modern and more primitive traits.

This situation reminds me of the search for the earliest modern humans. Many of these fossils also retained primitive features, which has made it difficult for anthropologists to decide which ones are truly modern humans and which ones aren’t. Likewise, anthropologists now have to determine whether modern humans could have been more diverse near the end of the Pleistocene than they had previously thought or whether more hominid species were living back then than they had previously expected.

The skull of Sahelanthropus. What does its body look like? Image courtesy of Wikicommons

Hominid Hunting went on an unexpected hiatus in January. I’m finally back. For my first post, I thought I’d share what I’ve been thinking about for the past couple months: my fantasy fossil finds, or the hominid discoveries I’d most like to see. In no particular order:

1. The skeleton of Sahelanthropus: In 2002, anthropologists announced the discovery of a new hominid (PDF): Sahelanthropus tchadensis. Unearthed in Chad, the find was exciting because it was the first—and still only—hominid found west of Africa’s Rift Valley. And at six million to seven million years old, it was the earliest known hominid. But the species’ place in the hominid family tree is not secure. The original discovery consisted of a skull, jaw and a few isolated teeth. (Since then, researchers have found (PDF) a few additional jaws and teeth.) The position of the skull’s foramen magnum—the hole near the base of the skull where the spinal cord exits—is like that of a hominid, more forward under the skull, indicating an erect posture and upright walking. But to confirm Sahelanthropus‘ hominid status, and convince the skeptics that it’s not a non-hominid ape, scientists need to find the species’ post-cranial bones.

2. The skull of Orrorin: Around the same time that Sahelanthropus was discovered, researchers dug up another new hominid species, Orrorin tugenensis, in Kenya. Like Sahelanthropus, the hominid was very ancient, about six million years old. The discovery consisted of 13 fossils, including thigh bones, finger bones and isolated teeth and jaw fragments. The thigh bones show the telltale signs of walking upright while the rest of the known body looks more apelike, which is expected for a very early hominid. But to get a fuller picture of the species it would be nice to have a complete skull.

3. Hobbit DNA: Almost ten years after Homo floresiensis was discovered on the island of Flores in Indonesia, anthropologists still disagree about whether the hobbit was a distinct species of Homo or a diminutive modern human with a genetic growth disorder, perhaps microcephaly. Extracting DNA from one of the hobbit fossils would help resolve the debate, revealing whether or not its genetic blueprints match our own.

4. Fossils of a Denisovan: The study of the Denisovans has the opposite problem. A couple years ago, researchers discovered a potentially new hominid species based purely on its DNA. The DNA came from an isolated finger bone found in a cave in Siberia. The bone dates to between 30,000 and 48,000 years ago, a time when modern humans and Neanderthals could have lived in the area. But the genetic material didn’t match either species. So now anthropologists know there was a third type of hominid in Eurasia at this time—but they have no idea what it looked like.

5. Australopithecus skin: When researchers stumbled upon Australopithecus sediba in a South African cave, they found more than just a possible link between australopithecines and the genus Homo. Some of the 1.977-million-year-old fossils are covered in a thin layer that might be skin. If so, it would be the first time anyone has ever found fossilized soft tissue from an ancient hominid. To investigate the matter, a pair of scientists has started the open-access Malapa Soft Tissue Project to gather ideas on the best way to analyze the possible skin.

6. More Homo habilis and Homo rudolfensis fossils: Homo habilis is the earliest known member of the genus Homo, living 2.4 million to 1.4 million years ago in East and South Africa. It was given its Homo status largely because its brain was bigger than the Australopithecus brain. The species is somewhat controversial, however, with some researchers believing it really was a species of Australopithecus. The issue became even more confused when scientists decided that at least one Homo habilis fossil was different from all the others. A 1.8-million-year-old skull found in Kenya’s Lake Turkana region had a much larger brain size than any other Homo habilis—nearly 200 cubic centimeters bigger. Now some researchers place this and a few other specimens in the species Homo rudolfensis. But many questions remain. Are the two really different species or part of one variable species? Finding more of the big-brained skulls, with associated post-cranial bones, might help researchers determine how different the two forms really were.

7. The skeleton of Gigantopithecus: The largest ape that ever lived went extinct about 300,000 years ago. All researchers know about Gigantopithecus comes from a few jaws and teeth. Based on that scant evidence, some anthropologists think the ape might have stood 10 feet tall and weighed a whopping 1,200 pounds. But to more accurately determine how gargantuan the ape was, and how it moved, someone needs to find some of its post-cranial parts.

8. More Kenyanthropus fossils: In 1999, anthropologists found the skull of the 3.5-million-year-old Kenyanthropus platyops. Researchers classified the skull as a new hominid species because of its unique mix of apelike and humanlike traits. For example, the species had small earholes like a chimp’s but a much flatter face. Many anthropologists don’t agree with this classification. The skull was in bad condition when it was found, and some researcher think it is just a distorted Australopithecus afarensis skull. The only way to settle the matter is to find more skulls that look like the original, if Kenyanthropus really ever existed.

9. A chimp relative: Almost nothing is known about the evolution of chimpanzees after they split away from the human lineage. The lack of fossil evidence may be due to where chimpanzee ancestors likely lived—warm, wet forests where fossils are not often preserved. But in 2005, a pair of anthropologists reported they had found three isolated chimp teeth dated to 500,000 years ago. Whether these teeth belonged to modern chimpanzees (which would imply they are a very long-lived species) or a chimpanzee ancestor is unknown. But what’s interesting about the teeth is where they were found: the Rift Valley of Kenya. Half a million years ago this part of Africa was largely a savannah, indicating ancient chimps were not restricted to forests. Still, even with this discovery, next to nothing is known about chimp ancestry. More fossils, from an even older period, would be a great find.

10. Something unexpected: Of course, the most exciting fossil discoveries are the ones you don’t anticipate and make scientists rethink some aspect of human evolution.

This is just my personal wish list. What’s on yours?

The skull of Australopithecus sediba. Picture by Brett Eloff, courtesy of Lee Berger and the University of the Witwatersrand

For this last Hominid Hunting post of 2011, I reviewed recent human evolution research highlights to come up with my picks for the top 10 hominid discoveries of the year. While genetic breakthroughs have hogged the spotlight the past couple of years, good old-fashioned fossil and archaeological finds were front and center in 2011.

10. Earliest Modern Humans in Europe: Paleoanthropologists believe modern humans (Homo sapiens) came to Europe about 43,000 years ago. This date is based on the age of sophisticated stone tools, not human fossils. This year two teams dated European fossils that are in line with the age of the tools: A human upper jaw discovered in southern England in 1927 was dated to  44,000 years ago, and two molars unearthed in Italy were dated to 45,000 years ago. These fossils are the oldest known human remains on the continent.

9. The Arches of Australopithecus afarensis: There’s no doubt that Lucy and her species, Australopithecus afarensis, walked upright. But the degree to which these hominids walked on the ground has been debated. The discovery of a 3.2-million-year-old foot bone confirmed that Lucy and her kind had arched feet and therefore probably walked much like modern people. The researchers who studied the fossil say it indicates Australopithecus afarensis no longer needed to spend much time in the treetops; however, other researchers disagree, saying hominids at this time were still good tree climbers.

8. World’s Earliest Mattress: In a rock shelter in South Africa, archaeologists uncovered a 77,000-year-old mattress composed of thin layers of sedges and grasses, predating all other known mattresses by 50,000 years. Early humans knew how to keep the bed bugs out; the bedding was stuffed with leaves from the Cape Laurel tree (Cryptocarya woodii), which release chemicals known to kill mosquitos and other bugs.

7. Neanderthal Mountaineers: Neanderthals evolved many traits to deal with the cold; for example, their short limbs helped them conserve heat. A mathematical analysis revealed that short limbs may have also helped Neanderthals walk more efficiently in mountainous terrains. Specifically, the fact that Neanderthals had shorter shins relative to their thighs meant they didn’t need to lift their legs as high while walking uphill, compared to modern people with longer legs. “For a given step length, they [needed] to put in less effort,” said lead research Ryan Higgins of Johns Hopkins University.

6. The First Art Studio: Archaeologists working in South Africa’s Blombos Cave discovered early humans had a knack for chemistry. In a 100,000-year-old workshop, they found all of the raw materials needed to make paint, as well as abalone shells used as storage containers—evidence that our ancestors were capable of long-term planning at this time.

5. Australopithecine Females Strayed, Males Stayed Close to Home: In many monkey species, when males reach adolescence, they leave their home to search for a new group, probably as a way to avoid breeding with their female relatives. In chimpanzees and some humans, the opposite occurs: Females move away. Now it appears that australopithecines followed the chimp/human pattern. Researchers studied the composition of strontium isotopes found in the teeth of members of Australopithecus africanus and Paranthropus robustus. An individual consumes strontium through food and it is taken up by the teeth during childhood. Because the isotopes (different forms of the element) in plants and animals vary by geology and location, strontium can be used as a proxy for an individual’s location before adulthood. In the study, the researchers discovered that large individuals, presumably males, tended to have strontium isotope ratios typical of the area where the fossils were found; smaller individuals, or females, had non-local strontium isotope ratios, indicating they had moved into the area as adults.

4. Confirmation of Pre-Clovis People in North America: Since the 1930s, archaeologists have thought the Clovis people, known for their fluted projectile points, were the first people to arrive in the New World, about 13,000 years ago. But in recent years there have been hints that someone else got to North America first. The discovery of more than 15,000 stone artifacts in central Texas, dating to between 13,200 and 15,500 years ago, confirmed those suspicions. Corroborating evidence came from Washington State, where a mastodon rib containing a projectile point was dated this year to 13,800 years ago.

3. Denisovans Left A Mark in Modern DNA: The Denisovans lived in Eurasia sometime between 30,000 and 50,000 years ago. Scientists don’t know what they looked like; the only evidence of this extinct hominid group is DNA extracted from a bone fragment retrieved from a cave in Siberia. But this year, several studies revealed the mysterious population bred with several lineages of modern humans; people native to Southeast Asia, Australia, Melanesia, Polynesia and elsewhere in Oceania carry Denisovan DNA.

2. Out of Africa and Into Arabia: Traditionally, paleoanthropologists have thought modern humans left Africa through the Sinai Peninsula and into the Levant. But some researchers suggest our ancestors took a more southerly route, across the Red Sea and into southern Arabia. This year, several studies provided evidence pointing to this exit strategy. First, a team reported the discovery of 125,000-year-old stone tools in the United Arab Emirates. The researchers suggested humans ventured into Arabia when sea level was lower, making a trip across the Red Sea easier. (Geologists later verified the climate would have been just right at this time.) No fossils were found with the tools, but the scientists concluded they belonged to modern humans rather than Neanderthals or some other contemporaneous hominid. Another study this year complemented the finding: Paleoanthropologists also found stone tools, dating to 106,000 years ago, in Oman. The researchers say the artifacts match tools of the Nubian Complex, which are found only in the Horn of Africa. This connection implies the makers of those African tools, most likely modern humans, made the migration into Oman.

1. Australopithecus sediba, Candidate for Homo Ancestor: Last year, scientists announced the discovery of a new hominid species from South Africa’s Cradle of Humankind—Australopithecus sediba. This year, the researchers announced the results of an in-depth analysis of the 1.97-million-year-old species. They say a mix of australopithecine and Homo-like traits make Australopithecus sediba, or a species very similar to it, a possible direct ancestor of our own genus, Homo.

The outline of a mastodon skeleton, found at a pre-Clovis site in Washington, indicating where a spear hit the animal. Image courtesy of the Center for the Study of First Americans, Texas A&M University

Sometime near the end of the Pleistocene, a band of people left northeastern Asia, crossed the Bering land bridge when the sea level was low, entered Alaska and became the first Americans. Since the 1930s, archaeologists have thought these people were members of the Clovis culture. First discovered in New Mexico in the 1930s, the Clovis culture is known for its distinct stone tools, primarily fluted projectile points. For decades, Clovis artifacts were the oldest known in the New World, dating to 13,000 years ago. But in recent years, researchers have found more and more evidence that people were living in North and South America before the Clovis.

The most recently confirmed evidence comes from Washington. During a dig conducted from 1977 to 1979, researcher uncovered a bone projectile point stuck in a mastodon rib. Since then, the age of the find has been debated, but last month in the journal Science, Michael Waters of Texas A&M University and colleagues announced a new radiocarbon date for the rib: 13,800 years ago, making it 800 years older than the oldest Clovis artifact. Other pre-Clovis evidence comes from a variety of locations across the New World. Here’s a brief tour of some of the most important sites:

Ayer Pond, Orcas Island, Washington: While digging in a wetland in 2003, workers discovered the bones of ancient bison, later radiocarbon-dated to about 13,800 years ago. Cuts on the bones and other signs of butchering indicate humans were in the area at that time. The researchers speculate that the hunters dismembered the bison on top of a frozen pond, leaving the carcass behind to fall to the pond’s bottom when the ice thawed.

Debra L. Friedkin site, Texas: An excavation at this site yielded 15,528 artifacts dating from 13,200 to 15,500 years ago. Named the Buttermilk Creek Complex, these small, lightweight tools—an indicator that the artifacts were designed to be carried around a lot—do not resemble Clovis tools, the researchers reported earlier this year in Science. But they may be the type of artifacts which later developed into Clovis tools.

Monte Verde, Chile: One of the first challenges to the Clovis theory came from southern Chile. In the 1970s, archaeologists discovered the remains of a campsite that dated to about 14,000 years ago, but the age was contested. In 2008, researchers obtained new radiocarbon dates from seaweed associated with stone tools at the site, placing humans in Chile as early as 14,200 years ago.

Paisley Caves, Oregon: So far, all of the pre-Clovis sites lack human bones; the case for a human presence is based solely on the discovery of artifacts and butchered bones. The Paisley Caves in Oregon, however, contain a type of human remains: fossilized poop, or coprolites if you want to be more scientific (and polite). Fourteen coprolites at the caves resembled human coprolites based on size, shape and other physical features. DNA from the samples confirmed their human origin. Radiocarbon dating indicates people left the specimens behind between 14,000 and 14,270 years ago. Canid DNA in the coprolites suggests early Americans may have eaten dogs, wolves or foxes; alternatively, such animals later came by and urinated on the dung.

Meadowcroft Rockshelter, Pennsylvania: Just an hour’s drive from Pittsburgh, Meadowcroft may be the oldest site of human habitation in the New World. The first artifacts were found in the 1950s, and subsequent excavations unearthed small stone blades, flakes and a projectile point that date to as many as 15,200 years ago. Some researchers think humans first called the rockshelter home even earlier, about 16,000 years ago. To imagine what life was like for America’s earliest immigrants, you can take a tour of Meadowcroft, which is open to the public May through October.