A new study in Nature described 13 fossilized teeth from Ethiopia’s Ledi-Geraru site that belonged to both a primitive Homo and an unknown species of Australopithecus. The paper detailed teeth dated between 2.8 and 2.6 million years ago and added evidence that at least two early hominin lineages coexisted in the same region around 2.6 million years ago.
An international team of paleoanthropologists identified a previously unknown species of Australopithecus in Ethiopia that coexisted with early representatives of the genus Homo, reported Scientific American. The find consisted of ten teeth corresponding to the new Australopithecus species and three from a primitive Homo. The species remained unnamed due to the limited number of fossils.
Ledi-Geraru, in Ethiopia’s Afar region and a few dozen kilometers from Hadar - where the partial skeleton of Lucy was found - was known for earlier discoveries including a 2.8 million-year-old jawbone that was the oldest known human specimen and some of the oldest known stone tools made by hominins dating to about 2.6 million years. The Ledi-Geraru Research Project was directed by the University of Arizona, which led the project since 2002. The discovery team, led by Kaye Reed, a paleoecologist at Arizona State University, continued to search for more fossils at the site.
Researchers reported that the Ledi-Geraru Australopithecus teeth looked different from those of Australopithecus afarensis and Australopithecus garhi. Analyses of enamel, size, and shape revealed enough differences to distinguish them from other known species. The team concluded that the Ledi-Geraru Australopithecus teeth belonged to a new species rather than Australopithecus afarensis. They said they could not name the new species based on teeth alone and needed more complete fossils before that could happen, ideally a skull. “We need to find something with more characteristics, like a skull or a skeleton. I wish we had it already,” said Kaye Reed, a paleoecologist at Arizona State University and co-author of the study, according to EL PAÍS.
The fossils were precisely dated using volcanic sediments that covered the teeth. The ash contained feldspar crystals that allowed scientists to date the sediments. “We can date the eruptions that were happening on the landscape when they’re deposited,” said Christopher Campisano, a geologist at Arizona State University. “The geology provides essential age control for the deposits across 2.3 to 2.95 million years ago,” added Ramon Arrowsmith, a geologist at Arizona State University.
The team reconstructed a paleoenvironment of rivers lined with trees, wetlands, and prairies, supported by grazing animals and large herbivores whose dental enamel recorded a grass-based diet. They described a landscape where rivers migrated across vegetated terrain into shallow lakes that expanded and contracted over time, in contrast to the modern faulted badlands visible at Ledi-Geraru today.
By 2.5 million years ago there were three genera—Australopithecus, Paranthropus, and Homo—and multiple lineages overlapped in time and space. “The image that many have in mind, that of a progression from ape to Neanderthal to modern man, is false. Human evolution does not work like that; it is random and resembles a bushy tree, with life forms that adapt or go extinct,” said Reed.
Diet emerged as a key question. Reed’s team examined dental enamel to find out what these species ate, and analyses of enamel and dental wear could provide answers. “If they ate the same foods, in a relatively arid environment, one of them might have been forced to consume secondary foods or compete for food,” said Reed. “This last point is only speculation for now,” cautioned Reed.
Outside experts noted implications for early hominin geography and ecology. “The new paper tells us this is happening in Ethiopia … a really interesting time frame, because it’s maybe the earliest population of our genus Homo,” said John Hawks, an anthropologist at the University of Wisconsin-Madison. “The area offered resources Homo and Australopithecus could use. Grasslands and rivers would have provided water to drink, plants to eat and large animals to hunt. Right now, we can say very little with certainty about direct interaction between Australopithecus and Homo. We know that both genera sometimes overlapped in time and space, but there is no behavioral evidence linking the two,” said Frances Forrest, an archaeologist at Fairfield University in Connecticut.
The announcement rekindled debates about species identification from limited remains. Some experts argued that the teeth could correspond to evolved Australopithecus afarensis and that more cranial or mandibular remains were needed to confirm a new species. Tim White said the new conclusions were unconvincing, and María Martinón was also skeptical. Researchers Marina Martínez de Pinillos and Leslea Hlusko noted that when working with isolated teeth, it was easy to misinterpret the differences.
Ledi-Geraru revealed the oldest member of the genus Homo, a 2.8 million-year-old jawbone, confirming the antiquity of the lineage. “We know what the teeth and mandible of the earliest Homo look like, but that’s it. This emphasizes the critical importance of finding additional fossils to understand the differences between Australopithecus and Homo, and potentially how they were able to overlap in the fossil record at the same location,” said Brian Villmoare, a researcher in the Department of Anthropology at the University of Nevada, Las Vegas.
“Everything we find is a piece in the puzzle of human evolution,” said Reed, according to Live Science.
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