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The 3.5-million-year-old skull of Kenyanthropus platyops. Image: Pavel Švejnar/Wikicommons

Three and a half million years ago was the heyday of Australopithecus afarensis. But Lucy’s species may not have been alone. In 1999, researchers working in West Turkana, Kenya, uncovered a roughly 3.5-million-year-old hominid skull with a face too flat to belong to A. afarensis. The skull’s finders decided it must be a new species, Kenyanthropus platyops.

At the time, anthropologists disagreed over K. platyops‘ identity and place in the human family tree. While some researchers take the species as a sign that there was a diversity of hominid types around during the middle Pliocene epoch, others say the K. platyops skull is not actually a distinct species at all—it’s simply a distorted skull of an A. afarensis.

Where does the debate stand today?

In 2010, some of the original describers of K. platyops—Fred Spoor of the Max Planck Institute for Evolutionary Anthropology in Germany and Meave Leakey of the Koobi Fora Research Project—worked with Koobi Fora’s Louise Leakey to reanalyze the skull. In their new analysis, the team used CT scans of the skull to assess how distorted the fossil really is. Although the skull contains numerous cracks, the shape of the skull and teeth remain largely unaffected by the damage, the researchers reported in Proceedings of the Royal Society B.

With that in mind, Spoor and the two Leakeys compared the physical features of K. platyops to those of A. afarensis and six other extinct hominid species, in addition to modern humans, chimpanzees and gorillas. According to the researchers, the results confirmed that K. platyops was significantly different from other hominid species, mainly in its flat face, forward-facing cheekbones and small molars (over time, the molars got bigger and bigger in the many species of Australopithecus before getting small again in the genus Homo). Thus, the fossil deserves to be in its own species, they concluded.

Of course, one paper never really settles a debate in human evolution. The Smithsonian Human Origins Program, for example, doesn’t include K. platyops in its list of hominid species and categorizes the K. platyops skull as A. afarensis. Many scientists probably won’t be convinced unless more fossils matching K. platyops are found. There are some other fragments of teeth and skull from West Turkana that may belong to the species, but those fossils don’t really shed any further light on the issue.

For those who do accept K. platyops as a distinct hominid, there’s not much to say about the species. Given its age, it’s possible that K. platyops made the famous footprints preserved at Laetoli in Tanzania. The footprints reveal that some sort of hominid with a modern gait was alive at the time. The more popular theory, however, is that A. afarensis was the upright walker at Laetoli.

Regardless of K. platyops‘ status as a species, it’s not the only evidence that more than one type of hominid lived in East Africa alongside Lucy. In April, researchers unearthed a 3.4-million-year-old hominid foot in Ethiopia that retained too many features related to climbing to be the foot of  A. afarensis. Who knows—maybe it belonged to K. platyops.

A piece of the elbow from Australopithecus anamensis found in northern Kenya. Image courtesy of Wikicommons

Kenya is a hotspot of human evolution. Birthplace of famed fossil hunter Louis Leakey, the country is home to the remains of at least seven hominid species. Here’s a look at Kenya’s top fossil finds:

1. Orrorin tugenensis: In 2001, a team of researchers reported they had unearthed more than a dozen hominid fossils in the Tugen Hills of western Kenya. The bones date to 5.8 million to 6.2 million years ago, making them some of the oldest hominid fossils. The team, led by Brigitte Senut of the National Museum of Natural History in Paris and Martin Pickford of the Collège de France, determined that they had found a hominid based largely on the species’ thigh, which had telltale features related to walking upright. They named the new species Orrorin tugenensis, meaning “original man in the Tugen region” in the local language. In 2008, an analysis confirmed that the species was indeed capable of walking bipedally. That means Orrorin is in the running for the title of our earliest hominid ancestor.

2. Australopithecus anamensis: A probable direct ancestor of Australopithecus afarensis, A. anamensis lived in East Africa 3.9 million to 4.2 million years ago. The first fossil of this species was uncovered at the site of Kanapoi in northern Kenya in 1965, but the excavators didn’t know what to make of it. Almost 30 years later, in 1994, paleoanthropologist Meave Leakey’s team found similarly aged fossils in the nearby site of Allia Bay. Leakey concluded that the Kanapoi and Allia Bay fossils belonged to a previously unrecognized species that lived a few hundred thousand years before Lucy.

3. Kenyanthropus platyops: Meave Leakey’s team found another new hominid species in 1999. Justus Erus, one of Leakey’s field assistants, found a skull broken in two halves in the West Turkana region. The 3.5-million-year-old skull had many primitive features, including a small brain. But it had several surprisingly modern-looking traits, such as a flat face and small cheek teeth normally associated with the genus Homo. Since then, no other K. platyops specimens have been identified. This has led some researchers to conclude the species isn’t its own species at all. Instead, it may be just a damaged, distorted A. afarensis skull.

4. The Black Skull: In 1985, paleoanthropologists Alan Walker and Richard Leakey discovered a 2.5-million-year-old hominid skull in the Lake Turkana region. Known as the Black Skull, the cranium was darkened by manganese minerals in the soil where it was unearthed. The skull, plus several isolated jaws previously found in the area, resembled the so-called robust hominids—Paranthropus boisei and Paranthropus robustus. The Black Skull had massive molars, flat cheeks and a large jaw. In addition, it had a thick ridge of bone running lengthwise from the top to the base of the skull, called a sagittal crest, where enormous chewing muscles attached. Many researchers think these fossils belong to a species called Paranthropus aethiopicus, a likely ancestor of the later Paranthropus species. Others disagree (PDF) and argue the species’ true name should be Australopithecus aethiopcus. These researchers say the Black Skull is too primitive to be the ancestor of the robust hominids. And their similarities are superficial—an example of parallel evolution, when two closely related species evolve similar characteristics due to similar environmental pressures.

5. The earliest Homo fossil: In 1967, paleoanthropologist Andrew Hill found a bone fragment in the Chemeron Formation of the Tugen Hills. The bone came from the temporal region of a hominid skull, the area near the ear. Comparisons with australopithecines and later species of Homo indicate the bone is probably some early form of Homo. With an age of 2.4 million years, it’s the earliest known Homo specimen.

6. Homo rudolfensis: At the Koobi Fora site in northern Kenya, Bernard Ngeneo found an unusual skull, known as KNM-ER 1470, in 1972. Dating to 1.9 million years ago, the skull’s owner lived at the same time as Homo habilis, the earliest known species of Homo. But the skull’s larger brain size and larger cheek teeth—characteristic of the earlier australopithecines—have led some anthropologists to classify KNM-ER 1470 as a separate species: H. rudolfensis.

7. Turkana Boy: Unearthed in 1984 by prolific fossil hunter Kamoya Kimeu in West Turkana, Turkana Boy is a nearly complete skeleton of an approximately 9-year-old Homo erectus child that lived 1.6 million years ago. The skeleton has helped researchers demonstrate H.erecuts was the first hominid to have a tall body and long legs: Scientists estimate the child was over 5 feet tall when he died and likely would have reached 6 feet had he lived to be an adult.

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?