Lucy, it turns out, had company _ another prehuman that also walked but spent more of its time in trees. 
 
 This image provided by the Cleveland Museum of Natural History shows a bone fragment from a 3.4-million-year-old partial foot recovered during an excavation in Ethiopia. A new study determined that the... (Associated Press) 
 
 Until now, there was no proof of another human relative living around the same time as the species made famous by the Lucy skeleton. But a fossil discovery reveals there was another creature around 3 million years ago and it gives new insight into the evolution of a key human trait _ walking on two legs. 
 
 The creature came to light when an international team of researchers unearthed a partial foot in eastern Africa. Like Lucy, it walked upright, but had a grasping foot that it used to climb tree branches. Scientists said it's now clear that various human relatives experimented with upright walking. 
 
 "This is just another window into solving the problem of how we got from a primitive foot to the modern human foot," said Bruce Latimer of Cleveland's Case Western Reserve University, who helped discover the fossil remains. 
 
 Various hominin species have co-existed throughout human evolutionary history, but this is the first sign of another during Lucy's time. 
 
 So what was this tree-climbing and ground-dwelling creature? Scientists don't yet know because no skull or teeth have been recovered to make a determination. But it's clear the foot did not come from Lucy's species, Australopithecus afarensis. 
 
 It's rare to find prehuman feet because bones are fragile and don't preserve well. So American and Ethiopian scientists led by the Cleveland Museum of Natural History were excited when they excavated eight foot and toe bones in 2009 in the remote Afar region of Ethiopia, 30 miles north of where Lucy was discovered in 1974. 
 
 By analyzing the bone structure and dating the surrounding dirt, the team concluded the fragments came from the right forefoot of a human relative that lived 3.4 million years ago. While Lucy had humanlike feet, this creature was less advanced. 
 
 The discovery was detailed in Thursday's issue of the journal Nature. The authors did not name the new species because they know so little about it. 
 
 "This find is the first good evidence that there was a second, different species lineage" at that time, said Tim White, director of the Human Evolution Research Center at the University of California, Berkeley, who had no role in the discovery. 
 
 The ability to walk upright is a key feature that separates humans from other great apes. That a different human relative ambled around the same period as Lucy suggests upright walking evolved more than once, scientists said. 
 
 Bipedalism "was a complicated affair and not just a `one-off' occurrence," William Harcourt-Smith of the American Museum of Natural History in New York, who was not part of the study, said in an email. 
 
 Over the past millions of years, the human foot has changed to give us a springy step. We have a stout big toe that lines up with the other toes. We also have a stable heel and an arch that distributes our weight when we walk, run or jump. 
 
 The new specimen's foot resembled that of Ardi, short for Ardipithecus ramidus, a species that lived a million years earlier than Lucy in what is now Ethiopia. But scientists don't know whether it is a descendant or close relative. Like Ardi, its big toe is set apart from the rest of its foot, allowing it to grip tree branches, and it had no arch. There are signs in the bones and joints that it walked on two legs _ at least some of the time. Instead of pushing off from the big toe like modern human, it took off from the outside of its feet. 
 
 Scientists said it's hard to glean what its stride was like without knowing the shape of its ankles, knees and hips. But it likely was not very efficient and moved around awkwardly. Without a foot arch, it also could not travel as far as Lucy. 
 
 While the 3-foot 6-inch (1.06-meter) Lucy spent some time in the forest, her vastly different feet meant that she was better adapted and more comfortable wandering around open fields than the newly discovered creature was. 
 
 Lucy discoverer Donald Johanson called the new find "one of those fascinating evolutionary experiments" that tried walking but never fully committed. 
 
 It "didn't seem to want to make up its mind whether it wants to live in the trees or on the ground," said Johanson, founding director of the Institute of Human Origins at Arizona State University. 
 
 What are the chances the two interacted? If they met, scientists said they probably did not socialize, given their different lifestyles. 
 
 "They went on with their own lives," Johanson said. 
 
 ___ 
 
 Follow Alicia Chang's coverage at http://www.twitter.com/SciWriAlicia ||||| Image caption Over three million years ago, Ethiopia's Afar region was wooded and had lakes 
 
 Scientists have obtained a fascinating new insight into the evolution of humans and our ability to walk. 
 
 It comes from the fossilised bones of a foot that were discovered in Ethiopia and dated to be 3.4 million years old. 
 
 The researchers say they do not have enough remains to identify the species of hominin, or human ancestor, from which the right foot came. 
 
 Butthey tell Nature journalthat just the shape of the bones shows the creature could walk upright at times. 
 
 The fossil haul consists of eight elements from the forefoot - bones such as metatarsals and phalanges. 
 
 The specimens were pulled from clay sediments at Burtele in the central Afar region, about 520km north-east of the capital Addis Ababa. 
 
 It is a significant discovery because it demonstrates there was more than one pre-human species living in East Africa between three and four million years ago, each with its own method of moving around. 
 
 Image caption The eight elements are all from the forefoot 
 
 The other creature was the famous "Lucy" animal (Australopithecus afarensis), whose remains were first identified in the Afar in the 1970s. 
 
 Lucy's body was built for walking. Her big toe was aligned with the other four digits of the foot, and she had a human-like arch that allowed for very efficient locomotion. 
 
 The owner of the partial foot from Burtele was notafarensis; that can be said definitively. 
 
 The fossils indicate it had no arch and the big toe was opposed to the other digits, enabling the animal to grasp branches in a tree. 
 
 But the fact this creature could and would walk on the ground is evidenced by the nature of the bone joints. These were arranged such that the foot could push off, or toe-off - something only humans do as they walk, and something flat-footed apes cannot achieve. 
 
 "If you look at the lateral metatarsal head along with the proximal toe bone, the phalanx - that particular joint is really unique in hominids," explained team member Dr Bruce Latimer of Case Western Reserve University, US. 
 
 "You can see it's a very different kind of a joint, because when you toe-off and push forward in that last phase of walking, your toes are highly flexed. In order to achieve that, you have to change the base of the phalanx and the metatarsal head - you have to change both sides of the joint. And it's a highly characteristic type of change that we can pick out immediately," he told the BBC. 
 
 The scientists can only speculate as to identity of the Burtele species. Without skull and teeth elements, a formal classification is impossible. 
 
 The team says the animal's morphology is reminiscent in some respects to a 4.4-million-year-old creature known asArdipithecus ramidus. Although, again, it is notramidus. 
 
 "It may be a relic species that was lingering around until 3.4 or 3.3 million years ago, and which had its origins way back inArdipithecus ramidustimes," suggested team leader Dr Yohannes Haile-Selassie. 
 
 Image caption The initial find was made in 2009. The analysis has continued since then 
 
 "But obviously we cannot put it into theArdipithecusgenus or call it aramidusspecies because we do not have any craniodental elements associated with this foot. 
 
 "We've kept digging at the Burtele site; we have a few isolated teeth, but that's all," the Cleveland Museum of Natural History curator told BBC News. 
 
 It is, though, a remarkable thought that there were these two very distinct species effectively rubbing shoulders with each other 3.4 million years ago in what is now Ethiopia. 
 
 The landmark Lucy specimen unearthed in 1974 was found at Hadar, about 50km from Burtele. Other remains ofafarensishave been discovered closer still. 
 
 Dr Isabelle De Groote is a palaeoanthropologist at London's Natural History Museum. 
 
 "I think this is really exciting," she said. 
 
 "We have so few foot remains, they so rarely preserve, that we tend to take great leaps through evolution where there are no specimens at all representing long periods of time," she commented. 
 
 "This new foot helps elucidate the process of how the bi-pedal foot evolved. We can see something of the sequence in how changes to bones occurred." 
 
 Jonathan.Amos-INTERNET@bbc.co.uk and follow me onTwitter
– Lucy was not alone. Scientists have unearthed fossilized bones that they believe must have belonged to the foot of another pre-human species that walked upright around 3 million years ago, the AP reports. It's the first evidence of such a species during that era since the one made famous by the Lucy skeleton. This foot clearly comes from a different species, but like Lucy its foot was designed to both walk and grab tree branches, with an opposable toe. The bones were discovered in Ethiopia, and dated to 3.4 million years ago, according to the BBC. For now, scientists can't classify the creature further, because they haven’t found its skull. "We've kept digging," says the curator of the Cleveland Museum of Natural History. "We have a few isolated teeth, but that's all." Still, even this limited find "is really exciting," one London palaeoanthropologist says. "This new foot helps elucidate the process of how the bi-pedal foot evolved."