Latest news with #human evolution
Daily Mail
a day ago
- Science
- Daily Mail
Mysterious species found living alongside our earliest ancestors deemed missing link in evolution
A lost chapter in human evolution has been discovered among a collection of teeth that dates back 2.8 million years. Researchers from Arizona State University announced that they have found a previously unknown species of ancient humans that appear to have coexisted with members of the genus Homo, our direct ancestors, in Africa. The team added that this era, between 2.6 and 2.8 million years ago, was a critical period in human evolution because it marked the earliest appearance of the Homo species ever found. Researchers also discovered the oldest known stone tools at the Ledi-Geraru site in the Afar region of Ethiopia. In 2013, another team unearthed a 2.8-million-year-old Homo jawbone at the same site. However, the 13 teeth uncovered here recently do not belong to our direct ancestors. Instead, the research team found that they came from a new member of the Australopithecus species, a group closely related to modern humans who lived in Africa between two and four million years ago. Unlike previous fossils from the species Australopithecus afarensis, these teeth were noticeably different, showing that a new evolution of early humans developed in this region and overlapped with members of our family tree. Researchers said this lost Australopithecus species suggests that human evolution was complex, with multiple species coexisting, not just a simple progression from ape to human. The most famous member of the Australopithecus afarensis species has been a fossil named 'Lucy,' whose fossil skeleton was discovered in 1974 in Hadar, Ethiopia. Australopithecus walked upright, a key human trait, but examinations of skull fragments have found they had smaller brains and ape-like features, such as larger teeth and robust jaws for chewing tough plants. However, researchers have not been able to find any fossils at the Ledi-Geraru site that match Lucy's species. The differences in the 13 Australopithecus teeth unearthed there, along with the presence of the Homo species, suggest that Lucy's species did live beyond 2.95 million years ago, according to the study in Nature. ASU paleoecologist Kaye Reed said: 'This new research shows that the image many of us have in our minds of an ape to a Neanderthal to a modern human is not correct — evolution doesn't work like that.' 'Here we have two hominin species that are together. And human evolution is not linear; it's a bushy tree, there are life forms that go extinct,' Reed added in a statement. The 'bushy tree' theory Reed mentioned refers to the concept of multiple early human species living simultaneously in ancient times. Some would go extinct while others would lead to the development of modern humans, like the species Homo. Researchers added that the new fossils don't represent a single 'missing link' but rather show evidence of diverse overlap during this evolutionary period. 'We know what the teeth and mandible of the earliest Homo look like, but that's it,' Reed explained. '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,' the study author continued. The genus Homo includes modern humans and our closest extinct relatives. The Ledi-Geraru Homo fossils, including the new teeth and the previously found jawbone, revealed that early Homo individuals likely had slightly larger brains and smaller teeth than Australopithecus. This suggests that the human diet was already shifting millions of years ago towards more meat or softer plants than Lucy's species ate. These humans also learned to use primitive tools, which the ASU researchers also found at the site. The fossils' age was determined by dating volcanic ash layers containing feldspar crystals, a method that pinpoints the time of eruptions sandwiching the fossils. The Ledi-Geraru landscape, once a vegetated area with rivers and lakes, was much different than today's arid badlands. The ASU team noted that future research will focus on tooth enamel to explore diet and potential interactions between the Homo and Australopithecus, such as whether these species competed for food or peacefully lived in different ecological regions of Africa.
Yahoo
2 days ago
- Science
- Yahoo
Fossils show two types of ancient human ancestors lived at the same place and time. One was possibly an unknown species
Ancient, fossilized teeth, uncovered during a decades-long archaeology project in northeastern Ethiopia, indicate that two different kinds of hominins, or human ancestors, lived in the same place between 2.6 million and 2.8 million years ago — and one of them may be a previously unknown species. The discovery provides a new glimpse into the complex web of human evolution. Ten of the teeth, found between 2018 and 2020, belong to the genus Australopithecus, an ancient human relative. Meanwhile, three teeth, found in 2015, belong to the genus Homo, which includes modern humans, or Homo sapiens. The results were published Wednesday in the journal Nature. Such an overlapping of two hominins in the fossil record is rare, which had previously led scientists to believe that Homo appeared after Australopithecus, rather than the two being contemporaries. Australopithecus species walked upright much like modern humans, but had relatively small brains, closer in size to those of apes. The emergence of Homo species, with their larger brains, is easy for people today to view as some sort of evolutionary upgrade on a path to modern humanity. But the coexistence of the two demonstrates that hominins developed, and lived, in multiple varieties at once. 'This new research shows that the image many of us have in our minds of an ape to a Neanderthal to a modern human is not correct — evolution doesn't work like that,' said study coauthor Kaye Reed, research scientist and president's professor emerita at the Institute of Human Origins and emeritus professor at the School of Human Evolution and Social Change at Arizona State University, via email. 'Here we have two hominin species that are together. And human evolution is not linear, it's a bushy tree, there are life forms that go extinct.' Since 2002, Reed has been a codirector of the Ledi-Geraru Research Project, which is focused, in part, on searching for evidence of early Homo species. In 2015, the team announced the discovery of the oldest known Homo jawbone at 2.8 million years old. It has also searched for later evidence of Australopithecus afarensis, which first appeared 3.9 million years ago, but there is no sign of these ancient human relatives in the fossil record after 2.95 million years ago — suggesting they went extinct before Homo's first appearance. Australopithecus afarensis is best represented by the famed fossilized remains of Lucy, discovered in 1974 in Ethiopia. Lucy was shorter than an average human, reaching about 3.3 feet (1 meter) in height, had an apelike face and a brain about one-third the size of a human brain. Her fossil showcased a mixture of humanlike and apelike traits and provided proof that ancient human relatives walked upright 3.2 million years ago. When the team discovered the Australopithecus teeth during two separate digs in 2018 and 2020, it compared them with species such as afarensis and another hominin group known as garhi, but they didn't match up. Instead, the scientists believe the teeth belong to a previously unknown species of Australopithecus that walked the Earth after Lucy — and alongside an early Homo species. 'Once we found Homo, I thought that was all we would find, and then one day on survey, we found the Australopithecus teeth,' Reed said. 'What is most important, is that it shows again, that human evolution is not linear. There were species that went extinct; some were better adapted than others, and others interbred with us — we know this for Neanderthals for sure. So anytime that we have another piece to the puzzle of where we came from, it is important.' Cracks in Earth's surface The teeth were found in Ethiopia's Afar region, a key place for researchers seeking answers about human evolution. A variety of preserved fossils have been found there as well as some of the earliest stone tools, Reed said. The Afar region is an active rifting environment — the tectonic plates beneath its earth are actively pulling apart and exposing older layers of sediment that shed light on almost 5 million years of evolution, Reed said. 'The continent is quite literally unzipping there, which creates a lot of volcanism and tectonics,' said study coauthor Christopher Campisano, associate director and associate professor at the Institute of Human Origins and associate professor at the School of Human Evolution and Social Change at Arizona State, in a video the school released. 'At 2 1⁄2, 3 million years ago, these volcanoes spewed out ash that contain crystals called feldspars that allow us to date the eruptions that were happening on the landscape when they're deposited.' The Australopithecus teeth documented in the new study were dated to 2.63 million years ago, while the Homo teeth are from 2.59 million and 2.78 million years ago. But the team is cautious about identifying a species for any of the teeth until it has more data and more fossils. 'We know what the teeth and mandible of the earliest Homo look like, but that's it,' said Brian Villmoare, lead study author and associate professor in the department of anthropology at the University of Nevada, Las Vegas, in a statement. '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.' The Australopithecus teeth broadly resembled those of the afarensis species in contour and the size of the molars, but features of the cusps and canine teeth had not been previously seen in afarensis or garhi teeth, Villmoare said. The teeth were also different in shape than those of any Homo species, or of the ancient human relative Paranthropus, known for its large teeth and chewing muscles. 'Obviously these are only teeth,' Villmoare said, 'but we are continuing field work in the hopes of recovering other parts of the anatomy that might increase resolution on the taxonomy.' Even just finding the teeth was a complicated task, according to Campisano. 'You're looking at little teeth, quite literally, individual teeth that look just like a lot of other of the little pebbles spread on the landscape,' he said in the video. 'And so, we have a great team of local Afars that are excellent fossil hunters. They've seen these things their entire lives walking around the landscape.' A blip for evolution The new study is important because it provides insight into a time frame from 3 million to 2 million years ago, a mysterious period in human evolutionary studies, said Dr. Stephanie Melillo, paleoanthropologist and assistant professor at Mercyhurst University in Pennsylvania. Melillo was not involved in this research, but she has participated in the Woranso-Mille Paleontological Research Project in the Afar Triangle of Ethiopia. Part of the problem in learning about this stretch of prehistory is how ancient layers of dirt were deposited over the course of history in eastern Africa. 'Erosion in rivers and lakes were at a low level and only a little bit of dirt was deposited in the Afar,' Melillo wrote in an email. 'That deposited dirt contains the fossils — of our ancestors and all the animals that lived with us. When there is little deposition, there are few fossils.' A key feature helping archaeologists to understand humanity's evolution are structural basins, or 'bowls' on Earth's surface that naturally collect layers of sediment better than the surrounding landscape does — like the Turkana Basin stretching across southern Ethiopia and northern Kenya, Melillo said. Previous research has found evidence to suggest that Homo and Paranthropus coexisted there 1.5 million years ago. The new study focuses on the Afar Depression, a basin to the north of the Turkana. 'This contribution by Villmoare and colleagues demonstrates that in the Afar there was also some other species around with Homo — but it isn't Paranthropus,' Melillo said. 'Instead, they identify this 'non-Homo' genus as Australopithecus. They do a very convincing job of demonstrating why the new fossils are not Paranthropus.' The study adds to growing evidence that Australopithecus was not roaming the Afar Depression alone, she said. A mysterious coexistence When Australopithecus and Homo were alive, the Afar Region, now mostly a semidesert, had much more seasonal variation in rainfall than it does today, Reed said. Millions of years ago, the environment there was still dominated by a dry season, but it was interrupted by a brief wet season. Rivers that carried water across the landscape existed for only part of the year. Few trees grew near the river, and the environment nearby was largely wetlands and grasslands. 'We have a fossil giraffe species that was eating grass, which probably indicates they were stressed as they eat trees and bushes almost every place else,' Reed said. 'Were the hominins eating the same thing? We are trying to find out by examining isotopes in their teeth and microscopic scratches on their teeth.' Understanding whether or not Homo and Australopithecus had the same food sources could paint a portrait of how our ancient ancestors shared or competed for resources, Reed said. The team also wants to try to identify which hominin made the stone tools found at the site. At the moment it's impossible to tell exactly how the two hominins coexisted, but Reed said she is hoping that future findings will provide more answers. 'Whenever you have an exciting discovery, if you're a paleontologist, you always know that you need more information,' Reed said. 'You need more fossils. More fossils will help us tell the story of what happened to our ancestors a long time ago — but because we're the survivors we know that it happened to us.' Sign up for CNN's Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more.
Yahoo
3 days ago
- Science
- Yahoo
Fossils show two types of ancient human ancestors lived at the same place and time. One was possibly an unknown species
Ancient, fossilized teeth, uncovered during a decades-long archaeology project in northeastern Ethiopia, indicate that two different kinds of hominins, or human ancestors, lived in the same place between 2.6 million and 2.8 million years ago — and one of them may be a previously unknown species. The discovery provides a new glimpse into the complex web of human evolution. Ten of the teeth, found between 2018 and 2020, belong to the genus Australopithecus, an ancient human relative. Meanwhile, three teeth, found in 2015, belong to the genus Homo, which includes modern humans, or Homo sapiens. The results were published Wednesday in the journal Nature. Such an overlapping of two hominins in the fossil record is rare, which had previously led scientists to believe that Homo appeared after Australopithecus, rather than the two being contemporaries. Australopithecus species walked upright much like modern humans, but had relatively small brains, closer in size to those of apes. The emergence of Homo species, with their larger brains, is easy for people today to view as some sort of evolutionary upgrade on a path to modern humanity. But the coexistence of the two demonstrates that hominins developed, and lived, in multiple varieties at once. 'This new research shows that the image many of us have in our minds of an ape to a Neanderthal to a modern human is not correct — evolution doesn't work like that,' said study coauthor Kaye Reed, research scientist and president's professor emerita at the Institute of Human Origins and emeritus professor at the School of Human Evolution and Social Change at Arizona State University, via email. 'Here we have two hominin species that are together. And human evolution is not linear, it's a bushy tree, there are life forms that go extinct.' Since 2002, Reed has been a codirector of the Ledi-Geraru Research Project, which is focused, in part, on searching for evidence of early Homo species. In 2015, the team announced the discovery of the oldest known Homo jawbone at 2.8 million years old. It has also searched for later evidence of Australopithecus afarensis, which first appeared 3.9 million years ago, but there is no sign of these ancient human relatives in the fossil record after 2.95 million years ago — suggesting they went extinct before Homo's first appearance. Australopithecus afarensis is best represented by the famed fossilized remains of Lucy, discovered in 1974 in Ethiopia. Lucy was shorter than an average human, reaching about 3.3 feet (1 meter) in height, had an apelike face and a brain about one-third the size of a human brain. Her fossil showcased a mixture of humanlike and apelike traits and provided proof that ancient human relatives walked upright 3.2 million years ago. When the team discovered the Australopithecus teeth during two separate digs in 2018 and 2020, it compared them with species such as afarensis and another hominin group known as garhi, but they didn't match up. Instead, the scientists believe the teeth belong to a previously unknown species of Australopithecus that walked the Earth after Lucy — and alongside an early Homo species. 'Once we found Homo, I thought that was all we would find, and then one day on survey, we found the Australopithecus teeth,' Reed said. 'What is most important, is that it shows again, that human evolution is not linear. There were species that went extinct; some were better adapted than others, and others interbred with us — we know this for Neanderthals for sure. So anytime that we have another piece to the puzzle of where we came from, it is important.' Cracks in Earth's surface The teeth were found in Ethiopia's Afar region, a key place for researchers seeking answers about human evolution. A variety of preserved fossils have been found there as well as some of the earliest stone tools, Reed said. The Afar region is an active rifting environment — the tectonic plates beneath its earth are actively pulling apart and exposing older layers of sediment that shed light on almost 5 million years of evolution, Reed said. 'The continent is quite literally unzipping there, which creates a lot of volcanism and tectonics,' said study coauthor Christopher Campisano, associate director and associate professor at the Institute of Human Origins and associate professor at the School of Human Evolution and Social Change at Arizona State, in a video the school released. 'At 2 1⁄2, 3 million years ago, these volcanoes spewed out ash that contain crystals called feldspars that allow us to date the eruptions that were happening on the landscape when they're deposited.' The Australopithecus teeth documented in the new study were dated to 2.63 million years ago, while the Homo teeth are from 2.59 million and 2.78 million years ago. But the team is cautious about identifying a species for any of the teeth until it has more data and more fossils. 'We know what the teeth and mandible of the earliest Homo look like, but that's it,' said Brian Villmoare, lead study author and associate professor in the department of anthropology at the University of Nevada, Las Vegas, in a statement. '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.' The Australopithecus teeth broadly resembled those of the afarensis species in contour and the size of the molars, but features of the cusps and canine teeth had not been previously seen in afarensis or garhi teeth, Villmoare said. The teeth were also different in shape than those of any Homo species, or of the ancient human relative Paranthropus, known for its large teeth and chewing muscles. 'Obviously these are only teeth,' Villmoare said, 'but we are continuing field work in the hopes of recovering other parts of the anatomy that might increase resolution on the taxonomy.' Even just finding the teeth was a complicated task, according to Campisano. 'You're looking at little teeth, quite literally, individual teeth that look just like a lot of other of the little pebbles spread on the landscape,' he said in the video. 'And so, we have a great team of local Afars that are excellent fossil hunters. They've seen these things their entire lives walking around the landscape.' A blip for evolution The new study is important because it provides insight into a time frame from 3 million to 2 million years ago, a mysterious period in human evolutionary studies, said Dr. Stephanie Melillo, paleoanthropologist and assistant professor at Mercyhurst University in Pennsylvania. Melillo was not involved in this research, but she has participated in the Woranso-Mille Paleontological Research Project in the Afar Triangle of Ethiopia. Part of the problem in learning about this stretch of prehistory is how ancient layers of dirt were deposited over the course of history in eastern Africa. 'Erosion in rivers and lakes were at a low level and only a little bit of dirt was deposited in the Afar,' Melillo wrote in an email. 'That deposited dirt contains the fossils — of our ancestors and all the animals that lived with us. When there is little deposition, there are few fossils.' A key feature helping archaeologists to understand humanity's evolution are structural basins, or 'bowls' on Earth's surface that naturally collect layers of sediment better than the surrounding landscape does — like the Turkana Basin stretching across southern Ethiopia and northern Kenya, Melillo said. Previous research has found evidence to suggest that Homo and Paranthropus coexisted there 1.5 million years ago. The new study focuses on the Afar Depression, a basin to the north of the Turkana. 'This contribution by Villmoare and colleagues demonstrates that in the Afar there was also some other species around with Homo — but it isn't Paranthropus,' Melillo said. 'Instead, they identify this 'non-Homo' genus as Australopithecus. They do a very convincing job of demonstrating why the new fossils are not Paranthropus.' The study adds to growing evidence that Australopithecus was not roaming the Afar Depression alone, she said. A mysterious coexistence When Australopithecus and Homo were alive, the Afar Region, now mostly a semidesert, had much more seasonal variation in rainfall than it does today, Reed said. Millions of years ago, the environment there was still dominated by a dry season, but it was interrupted by a brief wet season. Rivers that carried water across the landscape existed for only part of the year. Few trees grew near the river, and the environment nearby was largely wetlands and grasslands. 'We have a fossil giraffe species that was eating grass, which probably indicates they were stressed as they eat trees and bushes almost every place else,' Reed said. 'Were the hominins eating the same thing? We are trying to find out by examining isotopes in their teeth and microscopic scratches on their teeth.' Understanding whether or not Homo and Australopithecus had the same food sources could paint a portrait of how our ancient ancestors shared or competed for resources, Reed said. The team also wants to try to identify which hominin made the stone tools found at the site. At the moment it's impossible to tell exactly how the two hominins coexisted, but Reed said she is hoping that future findings will provide more answers. 'Whenever you have an exciting discovery, if you're a paleontologist, you always know that you need more information,' Reed said. 'You need more fossils. More fossils will help us tell the story of what happened to our ancestors a long time ago — but because we're the survivors we know that it happened to us.' Sign up for CNN's Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more. Solve the daily Crossword
Yahoo
3 days ago
- Science
- Yahoo
'It makes no sense to say there was only one origin of Homo sapiens': How the evolutionary record of Asia is complicating what we know about our species
When you buy through links on our articles, Future and its syndication partners may earn a commission. The story of our ancient ancestors began in Africa millions of years ago. But there are considerable gaps between the first and current chapters of that tale, and some anthropologists are looking to Asia to fill in missing information about how humans evolved. "The genus Homo evolved in Africa," Sheela Athreya, a biological anthropologist at Texas A&M University, told Live Science. But as soon as Homo left the continent, "all bets are off because evolution is going to treat every population differently." One bet Athreya is investigating is the notion that there wasn't a single origin of our species, Homo sapiens. Rather, the ancestors of today's humans living in different geographic regions took different evolutionary paths, before eventually coalescing into the human tribe we know today. Once humans left Africa, "you have so much complexity that it makes no sense to say there was only one origin of Homo sapiens," Athreya said. Key to this story is a different understanding of human evolution in Asia — and the possibility that Denisovans, a group of little-understood extinct human ancestors known from just a handful of fossils, were actually the same as a much earlier member of our family tree: Homo erectus, Athreya argues. Related: Strange, 300,000-year-old jawbone unearthed in China may come from vanished human lineage Early humans in ancient Asia There's a big gap in human evolutionary history. We know Homo evolved in Africa and that a human ancestor, Homo erectus, was already in Asia and parts of Europe by about 1.8 million years ago. But what happened in Asia between that point and the time when Homo sapiens arrived around 50,000 years ago? That picture is much less clear. To help fill it in, Athreya has considered the emergence of our species, Homo sapiens, during the Middle and Late Pleistocene epoch (780,000 to 11,700 years ago). Her "deep-dive" into the human fossil record of Asia has convinced her that there are evolutionary pathways in places like Java, Indonesia, that differ from the Pleistocene patterns seen in Africa and Europe. H. erectus reached Java at least 1.5 million years ago, and the species likely lasted there until 108,000 years ago. But the lack of more recent H. erectus bones doesn't necessarily mean they went extinct, Athreya wrote in a 2024 study with co-author Yousuke Kaifu, an anthropologist at the University of Tokyo. Instead, these Javanese H. erectus could have persisted until H. sapiens appeared in Sumatra as early as 73,000 years ago and interbred with them. The fossil record in China is similarly complicated. Around 300,000 years ago, there was a shift in what H. erectus fossils looked like, Athreya said. Skeletons in the Middle Pleistocene in China became more variable in form, and traits that were common in Western Eurasian groups like H. sapiens and Neanderthals, such as smoother bicuspid teeth, began to appear in these fossils. This means that — instead of completely dying out — H. erectus in China may have made a genetic contribution to populations living today, Athreya said, just as Neanderthals left genetic traces in people with European ancestry and Denisovans contributed DNA to people with Oceania ancestry. The idea isn't impossible, one expert told Live Science. Groups of ancient human relatives could have mated anywhere they met up, Adam Van Arsdale, a biological anthropologist at Wellesley College in Massachusetts, told Live Science. No matter where they lived, "I just think humans aren't that different" during the Pleistocene. What's more, anthropologists are starting to realize that many of these groups that looked very different could still have interbred. Twenty years ago, scientists would have said "there's no possible way" they could have interbred, Van Arsdale said. "And I just don't think we can assume that anymore." So far, no DNA has been recovered from H. erectus fossils, largely because most of their fossils are too old, so there's no genetic support for this idea. But emerging methods for extracting ancient proteins from fossils may soon make it feasible to identify some H. erectus genes. Another route to understanding the fate of H. erectus in Asia may be to look more closely at the enigmatic Denisovans. RELATED STORIES —Oldest wooden tools unearthed in East Asia show that ancient humans made planned trips to dig up edible plants —Ancient jawbone dredged off Taiwan seafloor belongs to mysterious Denisovan, study finds —140,000 year old bones of our ancient ancestors found on sea floor, revealing secrets of extinct human species Since the only known skull of a Denisovan looks similar, in many ways, to that of H. erectus, those two groups may actually be one and the same. "I don't think that genetics is going to find that Homo erectus was a separate dead-end lineage," Athreya said. "I would expect Denisovans to be Homo erectus." But until more work is done that combines DNA, artifacts and fossil bones in Southeast Asia, the full picture of human evolution cannot yet come into focus the way it has in places like Europe, Athreya said. Human evolution quiz: What do you know about Homo sapiens?
CNN
3 days ago
- Science
- CNN
Two types of ancient human ancestors coexisted more than 2 million years ago, fossils show
Ancient, fossilized teeth, uncovered during a decades-long archaeology project in northeastern Ethiopia, indicate that two different kinds of hominins, or human ancestors, lived in the same place between 2.6 million and 2.8 million years ago — and one of them may be a previously unknown species. The discovery provides a new glimpse into the complex web of human evolution. Ten of the teeth, found between 2018 and 2020, belong to the genus Australopithecus, an ancient human relative. Meanwhile, three teeth, found in 2015, belong to the genus Homo, which includes modern humans, or Homo sapiens. The results were published Wednesday in the journal Nature. Such an overlapping of two hominins in the fossil record is rare, which had previously led scientists to believe that Homo appeared after Australopithecus, rather than the two being contemporaries. Australopithecus species walked upright much like modern humans, but had relatively small brains, closer in size to those of apes. The emergence of Homo species, with their larger brains, is easy for people today to view as some sort of evolutionary upgrade on a path to modern humanity. But the coexistence of the two demonstrates that hominins developed, and lived, in multiple varieties at once. 'This new research shows that the image many of us have in our minds of an ape to a Neanderthal to a modern human is not correct — evolution doesn't work like that,' said study coauthor Kaye Reed, research scientist and president's professor emerita at the Institute of Human Origins and emeritus professor at the School of Human Evolution and Social Change at Arizona State University, via email. 'Here we have two hominin species that are together. And human evolution is not linear, it's a bushy tree, there are life forms that go extinct.' Since 2002, Reed has been a codirector of the Ledi-Geraru Research Project, which is focused, in part, on searching for evidence of early Homo species. In 2015, the team announced the discovery of the oldest known Homo jawbone at 2.8 million years old. It has also searched for later evidence of Australopithecus afarensis, which first appeared 3.9 million years ago, but there is no sign of these ancient human relatives in the fossil record after 2.95 million years ago — suggesting they went extinct before Homo's first appearance. Australopithecus afarensis is best represented by the famed fossilized remains of Lucy, discovered in 1974 in Ethiopia. Lucy was shorter than an average human, reaching about 3.3 feet (1 meter) in height, had an apelike face and a brain about one-third the size of a human brain. Her fossil showcased a mixture of humanlike and apelike traits and provided proof that ancient human relatives walked upright 3.2 million years ago. When the team discovered the Australopithecus teeth during two separate digs in 2018 and 2020, it compared them with species such as afarensis and another hominin group known as garhi, but they didn't match up. Instead, the scientists believe the teeth belong to a previously unknown species of Australopithecus that walked the Earth after Lucy — and alongside an early Homo species. 'Once we found Homo, I thought that was all we would find, and then one day on survey, we found the Australopithecus teeth,' Reed said. 'What is most important, is that it shows again, that human evolution is not linear. There were species that went extinct; some were better adapted than others, and others interbred with us — we know this for Neanderthals for sure. So anytime that we have another piece to the puzzle of where we came from, it is important.' The teeth were found in Ethiopia's Afar region, a key place for researchers seeking answers about human evolution. A variety of preserved fossils have been found there as well as some of the earliest stone tools, Reed said. The Afar region is an active rifting environment — the tectonic plates beneath its earth are actively pulling apart and exposing older layers of sediment that shed light on almost 5 million years of evolution, Reed said. 'The continent is quite literally unzipping there, which creates a lot of volcanism and tectonics,' said study coauthor Christopher Campisano, associate director and associate professor at the Institute of Human Origins and associate professor at the School of Human Evolution and Social Change at Arizona State, in a video the school released. 'At 2 1⁄2, 3 million years ago, these volcanoes spewed out ash that contain crystals called feldspars that allow us to date the eruptions that were happening on the landscape when they're deposited.' The Australopithecus teeth documented in the new study were dated to 2.63 million years ago, while the Homo teeth are from 2.59 million and 2.78 million years ago. But the team is cautious about identifying a species for any of the teeth until it has more data and more fossils. 'We know what the teeth and mandible of the earliest Homo look like, but that's it,' said Brian Villmoare, lead study author and associate professor in the department of anthropology at the University of Nevada, Las Vegas, in a statement. '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.' The Australopithecus teeth broadly resembled those of the afarensis species in contour and the size of the molars, but features of the cusps and canine teeth had not been previously seen in afarensis or garhi teeth, Villmoare said. The teeth were also different in shape than those of any Homo species, or of the ancient human relative Paranthropus, known for its large teeth and chewing muscles. 'Obviously these are only teeth,' Villmoare said, 'but we are continuing field work in the hopes of recovering other parts of the anatomy that might increase resolution on the taxonomy.' Even just finding the teeth was a complicated task, according to Campisano. 'You're looking at little teeth, quite literally, individual teeth that look just like a lot of other of the little pebbles spread on the landscape,' he said in the video. 'And so, we have a great team of local Afars that are excellent fossil hunters. They've seen these things their entire lives walking around the landscape.' The new study is important because it provides insight into a time frame from 3 million to 2 million years ago, a mysterious period in human evolutionary studies, said Dr. Stephanie Melillo, paleoanthropologist and assistant professor at Mercyhurst University in Pennsylvania. Melillo was not involved in this research, but she has participated in the Woranso-Mille Paleontological Research Project in the Afar Triangle of Ethiopia. Part of the problem in learning about this stretch of prehistory is how ancient layers of dirt were deposited over the course of history in eastern Africa. 'Erosion in rivers and lakes were at a low level and only a little bit of dirt was deposited in the Afar,' Melillo wrote in an email. 'That deposited dirt contains the fossils — of our ancestors and all the animals that lived with us. When there is little deposition, there are few fossils.' A key feature helping archaeologists to understand humanity's evolution are structural basins, or 'bowls' on Earth's surface that naturally collect layers of sediment better than the surrounding landscape does — like the Turkana Basin stretching across southern Ethiopia and northern Kenya, Melillo said. Previous research has found evidence to suggest that Homo and Paranthropus coexisted there 1.5 million years ago. The new study focuses on the Afar Depression, a basin to the north of the Turkana. 'This contribution by Villmoare and colleagues demonstrates that in the Afar there was also some other species around with Homo — but it isn't Paranthropus,' Melillo said. 'Instead, they identify this 'non-Homo' genus as Australopithecus. They do a very convincing job of demonstrating why the new fossils are not Paranthropus.' The study adds to growing evidence that Australopithecus was not roaming the Afar Depression alone, she said. When Australopithecus and Homo were alive, the Afar Region, now mostly a semidesert, had much more seasonal variation in rainfall than it does today, Reed said. Millions of years ago, the environment there was still dominated by a dry season, but it was interrupted by a brief wet season. Rivers that carried water across the landscape existed for only part of the year. Few trees grew near the river, and the environment nearby was largely wetlands and grasslands. 'We have a fossil giraffe species that was eating grass, which probably indicates they were stressed as they eat trees and bushes almost every place else,' Reed said. 'Were the hominins eating the same thing? We are trying to find out by examining isotopes in their teeth and microscopic scratches on their teeth.' Understanding whether or not Homo and Australopithecus had the same food sources could paint a portrait of how our ancient ancestors shared or competed for resources, Reed said. The team also wants to try to identify which hominin made the stone tools found at the site. At the moment it's impossible to tell exactly how the two hominins coexisted, but Reed said she is hoping that future findings will provide more answers. 'Whenever you have an exciting discovery, if you're a paleontologist, you always know that you need more information,' Reed said. 'You need more fossils. More fossils will help us tell the story of what happened to our ancestors a long time ago — but because we're the survivors we know that it happened to us.' Sign up for CNN's Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more.
