WASHINGTON – Fossil hunters have unearthed the fossil skeleton of a baby who died 3.3 million years ago, marking the first time scientists have found the nearly complete remains of a child of an ancient human ancestor.

The child, a girl who was about 3-years-old when she perished in what may have been a flash flood, provides an unprecedented window into human evolution, in part because she belongs to the same species as “Lucy,” one of the most famous hominid specimens in paleontology, experts said.

That prompted some scientists to refer to the new skeleton as “Lucy’s baby,” even though they estimate she lived some 150,000 years earlier. The researchers who found her in an Ethiopian desert named her Selam, which means peace in Ethiopian.

Although scientists have found individual bones and bone fragments of children from this and other species of human predecessors, and a few skeletons, the discovery represents one of the most complete individuals ever recovered, and by far the oldest. Bones of infants are so small and soft that few survive.

“I’m very excited,” said Zeresenay Alemseged of the Max Planck Institute in Leipzig, Germany, who led the international team reporting the find in today’s issue of the journal Nature. “This is a unique discovery in the history of paleoanthropology.”

Although scientists are still painstakingly extracting the fossilized bones from stone, they have already begun making striking discoveries, including a tiny throat structure that suggests that if the foot-and-a-half tall toddler cried out for its mother, her wails probably sounded more like a chimp than a human baby.

“If you imagine how this child would have sounded if it was crying out for its mother, its cry would appeal more to chimp ears than to human ears,” said Fred Spoor of University College in London, who is helping studying the remains. “Even though it’s a very early human ancestor, she would sound more apelike than humanlike.”

The remains also confirm how much of a hybrid these creatures were between humans and apes. While they had legs like humans that enabled them to walk upright on two feet, they had shoulders like gorillas that may have also enabled them to climb trees; while their teeth seem to have grown quickly, like chimps’ teeth, their brains may have matured more slowly, like humans.

“This confirms the idea that human evolution was not some straight line going from ape to human,” said Rick Potts of the Smithsonian Institution. “The more we discover, the more we realize that different parts evolve at different times, and some of these experiments of early evolution had a combination of humanlike and apelike features.”