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New fossil may be closest yet to ancestor of all great apes

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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 say. 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 Barcelona, Spain and his colleagues.

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 scanty 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 Pierolapithecus was discovered in Spain, Moyà-Solà believes that this species probably also lived in Africa. "Africa is the factory of primates. 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," he said.

The individual that the researchers discovered 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. Pierolapithecus’ 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, Pierolapithecus’ 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, Pierolapithecus’ shoulder blades lie 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 Pierolapithecus’ 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. Pierolapithecus’ 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 Pierolapithecus’ 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 sign of Pierolapithecus’ existence 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.

Ginger Pinholster | Quelle: EurekAlert!
Weitere Informationen: www.aaas.org

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