Revisiting a Renowned Skull From Early Human Homo Erectus

by AMNH on Apr 13, 2021 11:05 am

Two scientists in the field examine a specimen together.

University of Witwatersrand geologist Silindokuhle Mavuso (left) and study lead author Ashley Hammond (right) at the East Turkana site in Kenya.
A. Hammond/© AMNH

Nearly 50 years ago, scientists working in East Turkana in northern Kenya found a small skull fragment that became one of oldest pieces of evidence for Homo erectus, a very successful early human who roamed the world for nearly 2 million years. But some paleoanthropologists expressed skepticism about the age of the skull fragment—1.9 million years—arguing that it could have come from a younger fossil deposit, possibly moved to the spot where it was found by water or wind.

Now, a new study led by Museum Assistant Curator Ashley Hammond cements the age and origin of this renowned specimen and describes two new fossils found at the site. The specimens may be the earliest pieces of the Homo erectus skeleton yet discovered. Details are published today in the journal Nature Communications.

[UPBEAT MUSIC]

[An anthropological crew digs and plants orange landscaping flags in the dirt of a dry landscape. Three people brush dirt away from an area marked off and partially excavated. Four people look through what remains in a sifter after sifting out the dirt.]

[Dr. Ashley Hammond sits in her office in the Division of Anthropology, drawers of specimens are placed on the table next to her.]

ASHLEY HAMMOND (Assistant Curator of Biological Anthropology, Division of Anthropology): Fieldwork sometimes is not as glamorous as it might seem from movies.

[Back in the field, one crew member hands a metal basket of dirt and rocks to be sifted to another crew member.]

ASHLEY HAMMOND: Fieldwork is often in a very remote place–in East Africa, for instance, it is very hot and dry.

[Photographs of East African landscapes cycle onscreen: scrub brush and low trees on dry soil, a large rocky plateau in the hazy distance, craggy desert stretching out into the horizon.]

ASHLEY HAMMOND: But it’s a really magical environment. There’s an element of discovery everywhere you go. You know that every time you cross that next little ridge or go down into the next gully, you might find a fossil.

[The American Museum of Natural History’s logo appears over a desert landscape image, it is replaced with the title “Searching for Human Ancestors in East Africa” and subtitle “Paleoanthropologist Ashley Hammond”.]

[Hammond speaks from her office.]

ASHLEY HAMMOND: My name is Dr. Ashely Hammond and I am the Assistant Curator of Biological Anthropology at the American Museum of Natural History.

[Hammond picks up a gorilla skull from a specimen cabinet in an anthropology collections space and examines it.]

ASHLEY HAMMOND: I am a paleoanthropologist…

[Hammond measures a fossil with calipers.]

ASHLEY HAMMOND: …which means that I am a paleontologist who works on the fossil record…

[Hammond examines a model of a primate skull at the anthropology preparator’s desk.]

ASHLEY HAMMOND: …for humans and our relatives.

[The camera pushes in on three model skeletons–one of a primate, one of a human ancestor, and one of a modern human–at the entrance of the Museum’s Hall of Human Origins.]

ASHLEY HAMMOND: Everyone wants to find a hominin, a human ancestor.

[Photographs of Hammond on digs in various fieldsites.]

ASHLEY HAMMOND: So this involves fieldwork, trying to get out to field sites that are at the very early time periods during which hominins would have evolved.

[A Google Earth view of the Earth spins and zooms in on Eastern Africa, with a placemark labeled “Kenya”.]

ASHLEY HAMMOND: My fieldwork over the last five years or so has really been focused in Kenya.

The East African Rift Valley passes right through Kenya…

[The areas on the map where tectonic movement creates a geological rift are highlighted in white. The border of the country of Kenya appears, showing that much of the rift is located within that country.]

ASHLEY HAMMOND: …and this allows a lot of old ancient sediments to be uplifted and available for us to find new fossils.

[The outlines of Kenya and the East African Rift Valley disappear.]

ASHLEY HAMMOND: And the region that I work in in Turkana is especially great for this.

[A new placemark labeled “East Turkana” appears in northern Kenya, directly where the rift valley outline had been. The map zooms into East Turkana and fades into a photograph of the landscape.]

ASHLEY HAMMOND: It’s really, in my mind, the most important place in the world for studying ape and human evolution.

[An anthropology crew member sifts sediment in the field in East Turkana.]

ASHLEY HAMMOND: We have sediments that span the entire range during which apes and humans have evolved.

[The field crew sets out for the dig area and walks along looking for fossils.]

ASHLEY HAMMOND: The best way to look for fossils at our sites is essentially walking across the landscape and looking for locations where fossils are coming out of the ground.

[Hammond speaks from her office.]

ASHLEY HAMMOND: So when we find something and we recognize that it’s a hominin, typically the first thing I do is I tell everyone to stop and slowly back away.

[Hammond LAUGHS]

[A barefoot anthropology crew member brushes dirt away from a potential fossil.]

ASHLEY HAMMOND: Maybe even, depending on the state of the fossil, take off their shoes, and then we can work the surface more delicately.

[Two crew members on their hands and knees carefully brush dirt away from a dig site.]

ASHLEY HAMMOND: And we walk around, or crawl around, and flag all of the different pieces of bone on the surface.

[A crew moves slowly through an area, planting orange landscaping flags into the ground to mark pieces of fossil.]

ASHLEY HAMMOND: And then we go through and very carefully document and collect the fossil finds.

[The crew brushes, sifts, and takes note of the fossil finds.]

ASHLEY HAMMOND: After we leave the field, we go back to the National Museum of Kenya in Nairobi…

[Photograph of the exterior of the National Museum of Kenya, embossed text on the wall reads “Nairobi National Museum.”]

ASHLEY HAMMOND: …where the fossils are deposited for future generations to come and study.

[Photographs of storage shelves in the National Museum of Kenya where human ancestor fossils are kept.]

ASHLEY HAMMOND: But I want to continue to work on hominins year-round. So what we often do at the museum is laser scan different fossils…

[A small bone rotates on a laser scanner.]

[Hammond speaks to camera in front of the laser scanner, holding some primate bone specimens.]

ASHLEY HAMMOND: …and then turn them into 3D models that we can work on here in the United States.

So right now I am demonstrating our 3D scanner. It’s scanning actually a monkey bone.

[A hand secures the monkey bone in place on the scanner. A computer screen next to the scanner shows the 3D model of the monkey bone as it is being rendered.]

ASHLEY HAMMOND: And we can turn this monkey bone into a 3D rendering…

[A lab technician rotates the 3D rendering of the monkey bone on the computer screen.]

ASHLEY HAMMOND: …and use that as comparative data with some of our fossils.

[Hammond sits at a table with trays of primate fossil specimens, measuring one with calipers.]

ASHLEY HAMMOND: When you’re working with fossils, often they are very fragmentary. So you have to tailor your analyses based on what you have to work with.

[Hammond speaks to camera.]

ASHLEY HAMMOND: You have to be more creative.

[Computer screen capture of a 3D rendered femur bone.]

ASHLEY HAMMOND: So I developed some really advanced shape analysis techniques.

[Hammond looks at a 3D fossil rendering on a computer screen with a lab assistant.]

ASHLEY HAMMOND: Things like fitting a sphere to a very fragmentary joint surface to estimate joint size. And this allows us to really compare shapes across different species or specimens in a much more advanced way than possible in the past.

[Hammond speaks to camera.]

ASHLEY HAMMOND: I’m really focused on trying to piece together the evolutionary history of the ape and hominin pelvis.

[Hammond holds up a cast of a fossil primate pelvis.]

ASHLEY HAMMOND: The pelvis is really informative about the biology of an animal.

[Footage of several human ancestor skeleton casts in the Museum’s Hall of Human Origins, including Lucy, the Australopithecus.]

ASHLEY HAMMOND: It can tell you about what species you’re looking at. It can tell you about whether or not you’re looking at a male or a female. Sometimes you can even tell if an individual has given birth. And you can even get information about where an individual is from.

[Hammond handles fossils in her office.]

ASHLEY HAMMOND: I still think it’s a really big question about what the starting point for the human lineage looked like.

[Dioramas from the Museum’s Hall of Human Origins show models of human ancestors hunting and preparing food and clothing.]

ASHLEY HAMMOND: What kind of behaviors we were using, how we became bipedal and so forth.

[Hammond speaks from to camera.]

ASHLEY HAMMOND: So the only way to really get at that question is to get out and do more fieldwork.

[Back in the field, Hammond leads her crew to a fossil dig site.]

ASHLEY HAMMOND: So I’m very excited to get out with me and my crew and see what kind of fossils we can find.

“Homo erectus is the first hominin that we know about that has a body plan more like our own and seemed to be on its way to being more human-like,” said Hammond, a paleoanthropologist in the Museum’s Division of Anthropology. “It had longer lower limbs than upper limbs, a torso shaped more like ours, a larger cranial capacity than earlier hominins, and is associated with a tool industry—it’s a faster, smarter hominin than Australopithecus and earliest Homo.”

When the East Turkana skull specimen was found in 1974—well before fossil finds could be documented with GPS—limited notes and photos were taken. So Dr. Hammond and her team launched geological detective work, sifting through hundreds of pages from old reports and published research and combining those “clues” with satellite data and aerial imagery to pinpoint the locality.

They did not find any evidence of a younger fossil outcrop that may have washed into the area where the skull specimen was found, supporting the original age given to the fossil.

At the same time, fieldwork assisted by students and staff from the Koobi Fora Field School led to the discovery of two new hominin specimens within 50 meters of the reconstructed location. The specimens, a partial pelvis and a foot bone, potentially are H. erectus. They could be from the same individual, but there is no way to prove that after the fossils have been separated for so long. Still, they might be the earliest postcrania—“below the head”—specimens yet discovered for H. erectus.

Fingers holding an identification label above a partial pelvis.

“This kind of renewed collaboration not only sheds new light on verifying the age and origin of Homo erectus but also promotes the National Museums of Kenya’s heritage stewardship in research and training,” said Emmanuel Ndiema, the head of archaeology at the National Museums of Kenya, which co-directs the Koobi Fora Field School.

The researchers also collected fossilized teeth from other kinds of vertebrates, mostly mammals, from the area. From the enamel, the team analyzed isotope data to paint a better picture of the environment in which the H. erectus individual lived. The work suggests that this early H. erectus was found in a paleoenvironment that included primarily grazers that prefer open environments to forest areas and was near a stable body of water.