Is Pierolapithecus the Last Common Ancestor of Humans and Apes?

A news release is also available in Spanish, Japanese, French and Catalan.

BARCELONA, Spain—A new ape species from Spain called Pierolapithecus catalaunicus, or its close relative, may have been the last common ancestor to all living great apes, including humans, researchers said Thursday at a press briefing in Barcelona. The Spanish paleontology team describes its fossil find in the 19 November issue of the journal Science, published by AAAS, the nonprofit science society.

Like other great apes, Pierolapithecus had a stiff lower spine and other special adaptations for climbing. These features, plus the fossil's age of about 13 million years, suggest that this species was probably close to the last great ape ancestor, according to Salvador Moyà-Solà of the Miguel Crusafont Institute of Paleontology and the Diputación de Barcelona in Spain.

Moyà-Solà joined colleagues Thursday 18 November to brief reporters at Sala Noble Edifici del Rellotge in Barcelona, a site known locally for an appearance by Albert Einstein in the mid-1920s, after he had won the Nobel Prize. This week's event, organized by AAAS, attracted about 50 Spanish reporters plus inquiries from journalists throughout Europe and the United States.

Members of the research team have nicknamed the ape "Pau," the Catalan name for Pablo, but also the word for "peace." Moyà-Solà said that a journalist friend came up wit the name at about the time the Iraq war was starting in March 2003. During Thursday's briefing, the scientists displayed reproductions of about 40 bones and bone fragments, including Pau's ribs, fingers, toes and face.

The great apes, which now include orangutans, chimpanzees, gorillas and humans, are thought to have diverged from the lesser apes, a group that contains modern gibbons and siamangs, about 11 to 16 million years ago.

Fossil evidence from this time period, the middle Miocene epoch, is sparse, however, and researchers have long been searching for the great ape ancestors that emerged after this split.

The scant fossil record has revealed several contenders, including Kenyapithecus, and Equatorius or the older Morotopithecus and Afropithecus, but the fossils that do exist indicate that these ancient "hominoids" were more primitive than Pierolapithecus, Moyà-Solà said.

The relatively complete Pierolapithecus skeleton shows a variety of important features shared by modern great apes, according to the researchers.

"The importance of this new fossil is that for the first time all the key areas that define modern great apes are well-preserved," Moyà-Solà said.

Although Pau was discovered in Spain, Moyà-Solà believes that his species probably also lived in Africa.

"Africa is the factory of primates," he said. "In the fossil record of the lower and middle Miocene in Africa, we have found a fantastic diversity of primitive hominoids with monkey-like body structures. In Eurasia, apes appeared suddenly in middle Miocene—before then, primates there were nearly unknown. For that reason, the source area in my opinion is Africa."

Pau was probably male, weighed approximately 35 kilograms and from its tooth shape appears to have been a fruit eater. The skeleton was discovered at a new paleontological site, Barranc de Can Vila 1, near Barcelona.

Pau's ribcage, lower spine and wrist show key signs of specialized climbing abilities that link this specimen with modern great apes. In contrast, monkeys, which belong to a more primitive group, have more generalized, versatile movement abilities and lack these particular traits.

For example, the ribcage, or thorax, is similar to that of modern great apes because it is wider and flatter than a monkey ribcage, the researchers report.

"The thorax is the most important anatomical part of this fossil, because it's the first time that the modern ape-like thorax has been found in the fossil record," Moyà-Solà said.

Specimens of other apes, such as Proconsul or Equatorius, have included some rib fragments, "but the morphology is primitive, completely like monkeys," he added.

In addition, Pau's shoulder blades lay along its back, as do those of modern great apes and humans. In monkeys, the shoulder blades are on the sides of the ribcage, the way they are in dogs.

In both Pierolapithecus and modern great apes, the lumbar section of the lower spine is relatively short and stiff. The vertebrae in this part of the spine therefore differ from monkey vertebrae, which allow more flexion and extension. These adaptations would have affected Pau's center of gravity, making it easier to assume an upright posture and to climb trees, the researchers say.

Also, in Pierolapithecus and modern great apes, only one of the two forearm bones "articulates," or attaches flexibly, to the wrist. This trait allows a relatively large degree of hand rotation and probably helped with climbing, according to Moyà-Solà.

Pau's skull was also distinctly great ape-like, the authors say. The face is relatively short, and the structure of the upper nose lies in the same plane as the eyes. In monkeys, a ridge between the eyes interferes with the plane of vision.

Pierolapithecus also had some more primitive, monkey-like features, such as a sloped face and short fingers and toes. Moyà-Solà and his colleagues think this is a sign that various traits emerged separately and perhaps more than once in ape evolution. For example, climbing and hanging abilities are often thought to have evolved together, but Pau's short fingers indicate that it didn't do a lot of hanging. Hanging-related traits may have evolved several times, showing up later in great apes, the researchers propose.

The first clue to the new fossil was a canine tooth turned up by a bulldozer that was clearing the land for digging. "Paleontologists in Spain say 'you don't find a good fossil, the good fossil finds you,'" Moyà-Solà said.

Moyà-Solà's spouse and co-author, Meike Köhler, said Thursday that the area around Barcelona is a basin surrounded by hills and mountains, making it rich in Miocene Era fossils. It was Köhler who developed a series of pictures of Pau that imbue the ape with life and personality not usually seen paleontological illustrations. According to Moyà-Solà, the illustrations helped many people to form a quick emotional bond to the ape who might be their very distant relative.

In addition to Köhler, Moyà-Solà's coauthors are David M. Alba and Isaac Casanovas-Vilar of the M. Crusafont Institute of Paleontology in Barcelona, Spain; and Jordi Galindo of Palaeotheria, S.C.P. Provençals, in Barcelona, Spain. Alba is also at Palaeotheria, S.C.P. Provençals, in Barcelona.

The study was supported by the Diputació de Barcelona, Departaments d'Universitats i Recerca i de Cultura de la Generalitat de Catalunya, CESPA GR, Ministerio de Educación y Ciencia, Fundació La Caixa, Fundación Conjunto Paleontológico de Teruel, and the Researching Hominid Origins Initiative.

— Kathy Wren and Michaela Jarvis

18 November 2004