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An artist’s reconstruction of Purgatorius, a probable primate ancestor. Image: Nobu Tamura/Wikicommons

Finding the earliest primates isn’t easy. The first members or our order probably lived about 65 million years ago and were rat-sized critters known mainly from teeth. With such scant evidence, researchers have had a hard time classifying these creatures and making connections to modern primates. Still, scientists have identified dozens of early primate, or probable primate, species. If you’re unfamiliar with our earliest origins, here are five primates to know.

Purgatorius: Discovered at Montana’s Hell Creek Formation, this shrew-sized mammal lived roughly 65 million years ago at the end of the Cretaceous period. Purgatorius‘ place in the primate family tree is debated. Aspects of the genus’ teeth align it with a group of extinct, primate-like mammals called plesiadapiforms. Some scientists say that the number and variety of teeth Purgatorius had makes it a possible common ancestor to primates and plesiadapiforms. Last week, paleontologists from Yale University announced they found  the first known Purgatorius ankle bones. The researchers say the fossils reveal the animal had flexible feet like modern tree-living mammals do, implying the earliest primates were indeed arboreal animals as scientists suspected.

Altiatlasius: A few molars and a jaw fragment are all that’s known of this small mammal discovered in Morocco. Many paleontologists consider Altiatlasius, which lived some 57 or 56 million years ago, to be the first true primate. How the ancient primate relates to modern primate lineages is unclear. While some researchers believe it’s similar to a group of primitive tarsier-like primates, others think it might be an ancient forefather of monkeys and apes.

Teilhardina: Named for the French paleontologist Pierre Teilhard de Chardin, Teilhardina has been found at North American and Asian sites dating to almost 56 million years ago. Scientists group the genus with the omomyids, a family of tarsier-like primates that emerged during the Eocene epoch some 56 million to 34 million years ago. Last year, scientists reported they had unearthed a cache of Teilhardina fossils in Wyoming’s Big Horn Basin that included the first evidence that early primates had nails instead of claws. The tips of the animal’s finger and toe bones were flattened, indicating the presence of fingernails, the researchers reported in the American Journal of Physical Anthropology.

Notharctus: This North American genus lived about 50 million years ago and belonged to a family of lemur-like primates called adapiforms. Notharctus had a long tail, leaped from tree to tree and snacked on leaves. A report published in PLOS ONE in January described fossils from this primate that indicate it would have had something like a cross between a fingernail and a claw on its second toe—kind of like modern lemurs, lorises and bush babies (or galagos) that all have a “grooming” claw on their second toe. But it’s not yet clear whether Notharctus was on its way towards evolving a true grooming claw, or on its way towards evolving a true nail.

Eosimias: Discovered in China, Eosimias lived about 45 million years ago. The size and shape of its teeth suggest it was the earliest ancestor of the lineage leading to monkeys and apes (and us!). Fossils of its feet suggest Eosimias walked on all fours like a modern monkey.

Dating and mapping fossil finds is one way anthropologists track early human migrations. The bones from Qafzeh, Israel, (a drawing of one of the skulls, above) indicate Homo sapiens first left Africa more than 100,000 years ago. Image: José-Manuel Benito/Wikicommons

By 200,000 years ago, Homo sapiens had emerged somewhere in Africa. By 14,000 years ago, our species had spread to every continent except Antarctica. What happened in between—the pattern of where humans went and when—is still being worked out. To reconstruct the peopling of the world, anthropologists rely on several types of clues.

Fossils: The most obvious way to track our ancestors’ movements is to look for their physical remains. Researchers sketch out travel routes by mapping where the oldest human fossils are found. The earliest Homo sapiens bones outside of Africa come from a cave site in Israel called Qafzeh. Here the skeletons of both adults and children date to as far as 125,000 years ago. This first foray out of Africa didn’t last long. Humans disappeared from the fossil record outside of Africa for many tens of thousands of years, perhaps because the climate became too harsh. Fossils tell us humans made a successful, sustained exodus by at least 50,000 years ago. Human fossils found at Australia’s Lake Mungo site, for example, have been dated to between 46,000 and 50,000 years ago (PDF).

The problem with relying on skeletal remains to map early migrations is that the timing of our ancestors’ travels is only as good as the methods used to date the fossils. Sometimes scientists find bones in places that are not easily dated by geological techniques. And in some areas, fossils aren’t prone to preservation, so there are probably huge gaps in our knowledge of the paths early humans took as they spread around the world.

Artifacts: Archaeologists also look for the items people made and left behind. For example, stone tool discoveries suggest an alternative route out of Africa. For decades, scientists assumed humans left Africa via the Sinai Peninsula, but in the last several years some researchers have favored a “southern” route: leaving from the Horn of Africa, crossing the narrowest part of the Red Sea and entering into southern Arabia. Last year, archaeologists reported finding stone tools in Oman dating to roughly 106,000 years ago. At that time, the Arabian Peninsula was a much more hospitable place than it is today, home to numerous freshwater lakes. As the region became drier, people might have moved east into Asia or returned to Africa.

Of course, when the only remains at an archaeological site are tools, it’s hard to say with absolute certainty who made them. The researchers working in Oman noted that the tools they found in Arabia match the technology of modern humans found in eastern Africa about 128,000 years ago. The team made the case that the tool makers on either side of the Red Sea belonged to the same cultural group—and therefore the same species. But as anthropologists discover more species, such as the Hobbit or the Denisovans, that lived alongside modern humans outside of Africa up until a few tens of thousands of years ago, it becomes harder to say stone tools alone indicate the presence of Homo sapiens.

DNA: Genetic data can help fill in the holes in the human migration story that fossils and artifacts can’t address. Anthropologists collect DNA samples from different ethnic groups around the world. Next, they count up the genetic differences caused by mutations in certain sections of the genome. Groups that are more closely related will have fewer genetic differences, which implies they split off more recently form each other than they did with more distantly related groups. Scientists calculate when in the past different groups diverged from each other by adding up all of the genetic differences between two groups and then estimating how often genetic mutations occurred. Such analyses not only give a sense of when different parts of the world were first inhabited, but they can also reveal more intricate patterns of movement. For example, genetic data suggest North America was colonized by three separate waves of people leaving Siberia across the Bering Strait.

Genetic data are not foolproof, however. The estimated divergence times are only as accurate as the estimated mutation rate, which scientists still debate. In the early days of DNA studies, scientists used either mitochondrial DNA, passed down only by the mother, or the Y chromosome, inherited only from father to son. Neither of these types of DNA presented the full picture of what people were doing in the past, as mitochondrial DNA only tracks maternal lineages while the Y chromosome only follows paternal lines. Today, whole genome sequencing is beginning to allow researchers to trace entire populations.

Languages: Anthropologists use languages in methods analogous to studying DNA; they look for patterns of similarities, or differences, in vocabularies or other aspects of language. Earlier this year, researchers compared different languages within the Indo-European language family to determine where these languages arose. After assessing the relationship between the languages, the researchers considered the geographic ranges where those languages are currently spoken. They concluded that the Indo-European language family originated in what is today Turkey and then spread west into Europe and east into southern Asia as people moved into these areas. But such linguistic analyses may only track relatively recent migration patterns. For example, H. Craig Melchert, a linguist at the University of California, Los Angeles, told Science News that the Indo-European languages can only be traced back about 7,000 years.

Some of the Western Stemmed projectile points found in Oregon’s Paisley Cave. Image: Jim Barlow

A hundred years ago, archaeologists thought Native Americans came to North America only 5,000 years ago. That belief changed in the 1920s and 1930s as researchers started finding stone projectile points associated with the fossils of mammoths and giant bisons—animals that went extinct more than 10,000 years ago. For decades, the oldest known points dated to 13,000 years ago. Called Clovis points, they contained characteristic “flutes,” or long, concave grooves, where a spear locked into place.

More recent evidence reveals humans reached the New World, via the Bering Strait, by at least 15,000 years ago. These early Americans weren’t making Clovis points. Last week, archaeologists announced in Science another example of pre-Clovis technology.

The tools come from Oregon’s Paisley Caves. Dennis Jenkins of the University of Oregon and colleagues determined people were living in the area by at least 14,000 years ago based on the radiocarbon dates of human coprolites (fossilized dung) found in the cave. They also found projectile points of the same age or slightly older than Clovis points. Known as the Western Stemmed Tradition, these points are narrower, lack flutes and require a different chipping method to make than Clovis points.

The team suggests the Clovis and Western Stemmed points probably developed independently from an even earlier tool technology, with the Clovis originating in the Plains and Southeast and the Western Stemmed arising in the West. This fits with a discovery reported last year in Science. At the Debra L. Friedkin site in central Texas, archaeologists recovered more than 16,000 artifacts dating to 13,200 to 15,500 years ago. Among the artifacts were blades and two-sided flakes that Clovis tools could have evolved from, the researchers suggested. (A study published online in the Journal of Archaeological Science, however, challenges those dates and even argues that the artifacts may actually be Clovis tools.)

In other early American news, a team led by David Reich of Harvard Medical School reconstructed the ancestry of Native Americans living in North and South America. They reported their findings last week in Nature. Based on a genetic analysis of 52 modern Native American groups and 17 Siberian groups, the researchers concluded the majority of Native Americans descend from a single Siberian population. Arctic people who speak Eskimo-Aleut languages also inherited about half of their genetic material from a second wave of Siberian immigrants. Members of a third migration contributed to the gene pool of  Na-Dene-speaking Chipewyans of Canada. Finding multiple migrations complements previous genetic, archaeological and linguistic studies.

Of course, that doesn’t mean there were only three migrations to the New World. The researchers only looked at the ancestry of living Native Americans. There could be early migrating groups that didn’t leave behind living descendants. That’s something we may never know.

Cliff Palace at Mesa Verde National Park in Colorado. Image: Andreas F. Borchert/Wikicommons

The United States celebrates its 236th birthday this week. If you’re tired of the same old fireworks and cook outs, consider taking a trip to one of the country’s many archaeological parks to learn more about the people who lived in the U. S. hundreds or thousands of years before the Founding Fathers signed the Declaration of Independence. Here are a few suggestions:

Meadowcroft Rockshelter, Pennsylvania: This site may be the oldest known archaeological site in the United States, dating to 15,000 to 16,000 years ago. About an hour southwest of Pittsburgh, Meadowcroft offers tours of the rockshelter where you can see stone tools and the remains of fires that hunter gatherers made thousands of years ago.

Lubbock Lake Landmark, Texas: Not far from Texas Tech University, Lubbock Lake is an unusual archaeological site because of its complete, continuous record of human occupation over the last 12,000 years. The site’s earliest residents were the Clovis people, once considered to be the first human inhabitants of North America, and the Folsom people, who lived in the area about 10,800 years ago. Archaeologists at Lubbock have found Clovis and Folsom hunting and butchering sites, filled with stone tools and mammoth and bison bones. But excavations of the site are still ongoing, giving visitors a chance to see archaeologists in action.

Cahokia Mounds, Illinois: As a native of Illinois, I’m embarrassed to admit that I’ve never visited Cahokia, an area a few miles northeast of St. Louis that was first settled around 700 AD. By about 11oo, Cahokia had grown to be the largest pre-Columbian city in what is now the United States, home to as many as 20,000 people. (It was so big, in fact, that in 1250, it was larger than the city of London.) Cahokia was the center of Mississippian culture, a corn-farming society that built large, earthen mounds. Seeing such mounds, which served as platforms for houses, temples and other structures, is the highlight of a visit to Cahokia. The site’s centerpiece is the 100-foot-tall Monks Mound, the largest prehistoric earthwork in North America. If you don’t plan to be in Illinois anytime soon, there are plenty of other Mississippian mound sites you can visit, such as Alabama’s Moundville, Arkansas’ Parkin site (visited by Spanish explorer Hernando de Soto in 1541) and  Mississippi’s Emerald Mound.

Mesa Verde, Colorado & Chaco Canyon, New Mexico: While the Mississippians were constructing mounds, people in the Southwest were building stone and adobe pueblos. The Ancestral Puebloans first came to Mesa Verde in about 550 AD. For 600 years, the Puebloans lived and farmed on top of the mesa. But near the end of the 12th century, they started to live beneath cliff hangings. Today, the park is home to 600 of these cliff dwellings. The largest is Cliff Palace, consisting of 150 rooms and 23 kivas, walled, subterranean rooms used for ceremonies. They didn’t live there very long, however. By about 1300, a drought forced the Pueblo people to find new territories to the south and east. (Despite the wildfires blazing across Colorado, Mesa Verde National Park is open to visitors.)

More than 100 miles south of Mesa Verde, Chaco Canyon was a major political and spiritual center of Pueblo culture from 850 to 1250 AD. Instead of cliff dwellings, the site is known for its monumental and ceremonial architecture, particularly multistory “great houses” made out of stone. A self-guided driving tour of the park passes by six of the site’s most famous structures.

Clearly, this list of American archaeological parks is by no means exhaustive—just a few places that I’d like to visit. Where would you like to go?

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.