Article Contents:
- Introduction: a new challenge to the human family tree
- The story of the “Burtele foot” discovery
- A new species: Australopithecus deyiremeda
- Coexistence with Lucy: rewriting history
- Primitive traits and different adaptations
- Scientific debate: a new species or an intermediate stage?
- The need for more fossils
- Frequently asked questions
Introduction: a new challenge to the human family tree
Paleontologists have long believed that only a single species of early human ancestors, Australopithecus afarensis (known from the famous “Lucy” fossil), lived in East Africa between about 3 and 3.8 million years ago. Lucy was considered the “mother of humanity,” the ancestor from which all later species arose. But a new discovery in Ethiopia could turn this traditional view upside down.
A report published in the journal Nature indicates that a partial foot fossil dating back 3.4 million years belongs to a completely different species, meaning that at least two early human ancestor species may have shared the same landscape at the same time.
The story of the “Burtele foot” discovery
The story began in 2009, when Yohannes Haile-Selassie and his team were scouring the desert landscape of Burtele, a fossil site in the Afar region of Ethiopia. Stephanie Melillo, then a graduate student, spotted something striking: an ancient human-like foot bone.
“It was the fourth metatarsal half,” says Haile-Selassie, a paleontologist at Arizona State University, referring to the bone connecting to the fourth toe. After finding the other half, the team decided to thoroughly search the area, crawling on their hands and knees. The team eventually discovered eight pieces of a partial forefoot. They concluded that these fossils, dubbed the “Burtele foot,” did not belong to Lucy’s species (A. afarensis).
A new species: Australopithecus deyiremeda
Now, after gathering additional fossils from the Afar region, Haile-Selassie and his team have determined that the Burtele foot likely belongs to a distinct species they named Australopithecus deyiremeda.
This species was first named by Haile-Selassie and co-authors in 2015 based on upper and lower jaw fragments found in the region. At the time, researchers did not believe there was enough evidence to link the foot bones to this species. But since then, the team has discovered more fossils near where the foot was found, including fragments of the pelvis, skull, jaw, and additional teeth, which they also attributed to A. deyiremeda. The spatial proximity convinced the team that the foot must also belong to this species.
Coexistence with Lucy: rewriting history
“This is the most definitive evidence to show that multiple related species coexisted at the same time in our evolutionary history,” Haile-Selassie says. This discovery suggests that human evolution was not a simple straight line from one ancestor to another, but rather resembled a branching tree where different species lived side by side and competed for resources.
Fred Spoor, a paleontologist at the Natural History Museum in London, agrees that it is plausible to attribute the foot to A. deyiremeda, reinforcing the idea of coexistence.
Primitive traits and different adaptations
A. deyiremeda appears to have had more primitive traits than Lucy. Importantly, it had a grasping big toe, much like that of great apes, making it easier to climb trees. In contrast, Lucy’s foot was much more adapted for walking upright on the ground.
Some features of the A. deyiremeda fossils resemble an older species, Australopithecus anamensis, which lived 3.8 to 4.2 million years ago, more than they resemble Lucy.
Chemical analysis of A. deyiremeda teeth also indicates that it primarily ate plants from wooded areas, such as leaves, shrubs, and fruits. This is a less diverse diet than the mix of grassland and woodland foods consumed by Lucy. These differences in locomotion and diet may have allowed the two species to coexist without directly competing for the same resources.
Scientific debate: a new species or an intermediate stage?
Despite the compelling evidence, not all scientists agree that A. deyiremeda represents a unique species. Leslea Hlusko, a paleontologist at the Spanish National Research Center on Human Evolution in Burgos, points out that the dental features of A. deyiremeda show similarities to both the older A. anamensis and the younger A. afarensis.
She argues that this indicates A. deyiremeda may represent an intermediate stage between the two species rather than a unique species in its own right. “If you have an evolving lineage, this is exactly what you would expect: to have some traits of the previous species and some traits of the next species,” she says. Hlusko also notes that the Burtele foot is incomplete, and there are no known foot fossils from the older species (A. anamensis) for comparison, making it difficult to say for certain that the new bones come from a distinct species.
The need for more fossils
Whether it is a new species or not, experts agree that the picture of human evolution is far from complete. There are large gaps in the fossil record. There are very few relevant fossils from the period between 4.5 and 7 million years ago, which could reveal more details about the split between chimpanzees and human ancestors, Spoor says. There is a similar gap between 2.8 and 3.2 million years ago, when the genus Homo (modern humans) is thought to have emerged, Haile-Selassie says. Until more fossils are found, researchers can only draw a partial picture of human evolution from fragmented remnants of the past.
Frequently asked questions
1. What is “Lucy”?
Lucy is a famous fossil of a nearly complete skeleton belonging to the species Australopithecus afarensis, which lived about 3.2 million years ago and is considered one of the most important discoveries in the study of human evolution.
2. What is the new discovery?
The discovery is a partial foot fossil (“Burtele foot”) believed to belong to another species called Australopithecus deyiremeda, which lived at the same time and place as Lucy.
3. How does the “deyiremeda” foot differ from Lucy’s foot?
The deyiremeda foot has a grasping big toe, making it more adapted for climbing trees, whereas Lucy’s foot is more adapted for walking on the ground.
