“Basically, the story of the living apes is a mystery,” said Sergio Almécija, one of the authors of the new paper and a senior research scientist at the American Museum of Natural History in New York.

“We don’t have fossils that everyone agrees go to one of the branches of the living apes. At the same time, we have tons of fossils of apes. But no one agrees what they are because they are so different from the living ones.”

The incomplete fossilized remains used in the study come from the only known example of Pierolapithecus, discovered 20 years ago during expansion of a landfill in northeastern Spain, part of which has since become a vineyard.

It may be hard to imagine apes in this part of the world. But millions of years ago in the Mid-Miocene epoch, there were 10 times as many great ape species as there are today, and they were scattered across a much wider geographical area, including parts of Asia and Europe.

The apes of the Mid-Miocene also lived in woodlands that were far less hot and wet than the tropical forests where a small number of great apes now survive, all of them either endangered or critically endangered.

The Miocene landscape, however, shifted.

About 9.6 million years ago, changes to the climate wiped out much of the evergreen forest habitats in Eurasia. The loss “was disastrous for apes,” according to a paper in Nature Education Knowledge. Most apes disappeared from the region in an extinction event known as the Vallesian Crisis.

Pierolapithecus lived at an important moment, “just before the Earth’s climate changed and lots of these apes went extinct,” said Carol Ward, a professor of pathology and anatomical sciences at the University of Missouri School of Medicine who did not work on the paper.

Well-preserved fossils from this period are in short supply, Ward said. “The fossil record can be cruel. It gives us broken fossils, distorted fossils and fragmentary fossils.”

Such is the case with the lone set of remains from Pierolapithecus. The bones — which include the whole face, portions of the hands and pelvis, a foot, a few vertebrae and some ribs — were uncovered as workers created the landfill now known as Abocador de Can Mata near Barcelona.

“The face was a little smushed in different directions,” said Almécija, explaining that researchers suspected at first that bone fragments had been bent out of shape during the millions of years they lay buried beneath tons of sediment.

In the course of reconstructing Pierolapithecus, however, researchers realized that the bone fragments were not distorted. Many had shifted and separated from one another, leaving behind a kind of three-dimensional puzzle hampered by missing pieces.

CT scans have been used since the mid-2000s to reconstruct the images of long-extinct animals, including Sahelanthropus tchadensis, which, at about 7 million years old, is among the oldest known species assigned to the human family tree. But today’s equipment provides far better resolution, allowing scientists to achieve results that a decade ago would have been “almost impossible,” Almécija said.

The machine that scientists used to examine Pierolapithecus employs more-powerful X-rays than the traditional CT scanners found in a hospital. Known as a micro CT scanner, the device can penetrate dense material and produce much higher-resolution images.

Kelsey D. Pugh, a research associate at the American Museum of Natural History and a lecturer at Brooklyn College, led the CT analysis of Pierolapithecus.

“One part of the reconstruction is that you have the CT scans, which are of this damaged specimen, and you need to segment out what is bone and what is rock,” Pugh said. “You have to make decisions about which fragment should stay with which other fragment.”

Having assembled segments of bone, Pugh said, she then had to find the right position for each one, a task that took months and required “a lot of anatomical knowledge and a little bit of art.” One technique, called “mirror imaging,” made use of the symmetry in skulls. When fragments were absent from the left of the skull, she deduced what they ought to look like based on the fragments present on the right side.

The larger size of the pointed teeth called canines told the scientists they were looking at a male Pierolapithecus. It would have weighed about 75 pounds, roughly the size of a present-day female chimpanzee.

“The big surprise was that it was a mosaic,” said Almécija.

Pierolapithecus occupies an important branch on the tree of life, possessing a face similar to the great apes we know today — such as orangutans, chimpanzees and gorillas — and shorter hands like those of monkeys. Living apes have long hands and are able “to suspend themselves below the branches using their long, curved digits like hooks,” he said.

In the torso, Pierolapithecus was closer to living apes and humans, with the upright posture that helps humans walk on two feet and lets apes climb and suspend from tree branches, said Almécija. “Monkeys have more of a primitive body [form], like a cat or a dog.”

Pugh said what appears most distinctive about Pierolapithecus is the height of the face, in particular the distance between the areas of the skull that house the eyes and the nose. The eyes “sit quite high on the face,” Pugh said. “This is a feature we see in some other fossil apes, but it’s higher than most living apes.”

Kieran McNulty, an anthropology professor at the University of Minnesota who did not participate in the study, said that “this kind of detailed reconstruction is beneficial but takes a ton of work.”

The paper’s authors have made their CT scans of Pierolapithecus available to other scientists, a relatively rare practice in paleontology and paleoanthropology, McNulty said. This will allow other teams to attempt their own reconstructions of the species.

For scientists studying the evolution of hominids, the primate family that includes humans, the reconstruction and similar work should improve our understanding of the changes that have taken place over millions of years of ape evolution.

That will lead to “the really interesting question: Why did these changes take place?” Ward said. “Then we can start piecing together the story.”