For half a century, Australopithecus afarensis—better known to the world as “Lucy”—has enjoyed a celebrity status rare in paleontology. She was the anchor, the “mother of us all,” and the singular evolutionary bridge between the trees and the tarmac. But a new analysis of a 3.4-million-year-old foot fossil suggests Lucy’s monopoly on our ancestry is effectively over.
The study, published in Nature, definitively assigns the enigmatic “Burtele foot” to a separate species: Australopithecus deyiremeda. This isn’t just a taxonomic housekeeping update; it is hard evidence that the human family tree was never a straight line. It was a messy, experimental web of coexistence.
- Coexistence confirmed: The Burtele foot proves A. deyiremeda lived alongside Lucy, shattering the “single species” hypothesis for this era.
- Evolutionary divergence: While Lucy walked somewhat like us, this neighbor retained a grasping big toe, suggesting a hybrid lifestyle of walking and climbing.
- Niche partitioning: Isotope analysis reveals the two species avoided competition by eating completely different diets—Lucy grazed on grasses, while deyiremeda stuck to the forest.
The Hardware Variance: Why the Foot Matters
To understand why this finding matters, look at the biomechanics. For decades, the assumption was that by 3.4 million years ago, the “bipedal locomotion” update had been fully installed across the hominin line. Lucy’s feet were largely adapted for walking.
The Burtele foot, however, represents a different engineering approach. As detailed by ScienceDaily, this species possessed an opposable big toe—a feature usually associated with apes—yet moved on two legs by pushing off its second digit. This suggests that evolution was “A/B testing” different methods of bipedalism simultaneously. One species (Lucy) committed to the ground; the other (deyiremeda) hedged its bets, keeping one foot in the trees.
The “Roommate” Problem Solved
One of the biggest questions in anthropology is how two similar hominin species could occupy the same real estate in the Afar region without driving one another to extinction. The new data provides the answer: ecological separation.
Advanced isotope analysis of tooth enamel indicates a strict dietary boundary. While Lucy was a generalist, consuming a mix of C3 (forest) and C4 (savannah) resources, A. deyiremeda was a specialist, feeding almost exclusively on woodland sedges and fruits. They were neighbors, but they weren’t fighting over the same menu.
Forward Outlook: Is Lucy a Dead End?
The most disruptive implication of this study is genealogical. As noted in coverage by Science News, the presence of multiple contemporary species forces a re-evaluation of our direct lineage. If A. deyiremeda shows anatomical links to later species that Lucy lacks, it is entirely possible that Lucy’s species was an evolutionary dead end—a successful side branch that ultimately withered.
What to Watch Next:
- The “Lumpers vs. Splitters” War: Expect pushback from conservative paleoanthropologists who may argue these variations are sexual dimorphism rather than speciation. However, the isotope data makes that defense increasingly difficult to hold.
- The 3-Million-Year Gap: The pressure is now on to find fossils in the 3.0 to 2.8 million-year window. This is the “black box” where the genus Homo emerges. If we find Homo-like traits in A. deyiremeda descendants rather than Lucy’s, the textbooks will need a total rewrite.
- The “Bushy” Tree: We should anticipate further announcements of “new species” from archived fragments. Now that the precedent for coexistence is set, researchers will re-examine “outlier” bones from the 1970s and 80s that didn’t fit the Lucy template.
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