December 5, 2011
Human Evolution’s Cookie Monster, Oreopithecus
The skeleton of Oreopithecus bambolii. Image courtesy of Wikicommons
In the 1950s, a Swiss paleontologist named Johannes Hürzeler made an intriguing discovery. In a coal mine in the Tuscany region of Italy, he unearthed dozens of fossils, including a largely complete skeleton, belonging to an ape species named Oreopithecus bambolii (the name refers to the Greek word for hill or mountain, not the delicious chocolate cookie). A jaw of the species had been found in 1872, but the new treasure trove of fossils painted an unusual picture of the ape. The ape’s features implied it walked upright on two legs, just like humans. In fact, Hürzeler thought the nine-million-old species might have been a human ancestor. Others concluded it was just an ape that had evolved human-like characteristic due to convergent evolution. Still others who saw the fossils saw no human-like traits at all.
More than 50 years later, the debate continues.
In the 1990s, researchers Meike Köhler and Salvador Moyà-Solà, both of the Miquel Crusafont Catalan Institute of Paleontology in Spain, restored and reanalyzed a collection of Oreopithecus fossils housed in a Swiss museum. They claimed features of the ape’s pelvis, spine, legs and feet resembled those of australopithecines and modern humans, new evidence that Oreopithecus was capable of walking upright and probably did so habitually. Subsequent work on hand fossils suggested the ape also had the precise gripping skills that allow humans to thread a needle or turn a key in a lock.
Despite the similarities to humans, Köhler and Moyà-Solà argued that Oreopithecus was indeed an ape and not part of our lineage. The species evolved its unusual traits because of its unusual environment. Nine million years ago, during the Miocene epoch, the world’s climate was warmer and apes lived throughout much of Europe. The region of Italy where Oreopithecus was found was a swampy island at the time. Animals on islands often evolve unusual traits. (Scientists think the hobbit, Homo floresiensis, was exceptionally small because it lived on an island.) Oreopithecus lived in a place that lacked predators, so it was safer for the ape to travel on the ground. Waking upright, rather than climbing and swinging through the trees, also saved the ape energy, the researchers suggested. But the island was far from being a Shangri-La. The confined space meant food was limited and competition was fierce. Walking upright and precise manipulative abilities may have increased the ape’s foraging efficiency.
This view of Oreopithecus was not universally accepted. Other paleoanthropologists, such as Randall Susman of Stony Brook University in New York, interpreted the fossils differently. Where Köhler and Moyà-Solà saw human traits, Susman saw typical ape characteristics, such as long arms, short legs and curved toes, features associated with tree climbing. Some studies have suggested Oreopithecus may have been similar to modern orangutans. Susman also noted the Oreopithecus fossils are poorly preserved, and some of the bones are crushed, making it difficult to draw definitive conclusions.
Researchers have yet to find additional Oreopithecus fossils, so the debate remains in a stalemate. And Oreopithecus continues to be the most enigmatic ape of the Miocene.
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Two thoughts.
First: Every time we find an older, well-preserved hominin it seems to push back the origin of bipedal locomotion in primates. When I was young, it was presumed to be an adaptation that went hand-in-hand (chuckle) with tool use. Ardipithecus’ almost-upright locomotion was the latest big surprise. I wonder if Oreopithecus could possibly bear on the question? Is it possible that it evolved not in hominins but our common ancestor with chimpanzee line, but then been lost from that line?
Second: I find paleoanthropologists to be much too prone to excessive certainty. They might almost be partisan politicians, if they stuck to only two interpretations of the evidence. Why can’t they just do as researchers in other sciences are wont to do, and say of their favorite interpretation, “it’s one reasonable hypothesis,” or even “we don’t know yet”?
Comment by Jeff Michals-Brown — December 9, 2011 @ 10:40 pm
Jeff, you raise some interesting points. I agree that it’s probably best not to talk with too much certainty when it comes to human evolution. Every new find can rewrite what we thought we knew. In terms of Oreopithecus, if the fossils really are in such a poor state, it’s probably difficult to draw any definitive conclusions.
In terms of bipedalism being present in the last common ancestor of chimps and humans, I think it’s unlikely. Here’s why. Orangutans split from the African apes about 15 million years ago, then gorillas split from chimps+humans about 10 million years ago, and finally chimps and humans split some 7 million years ago. We know that orangutans and gorillas are not bipedal. If the last common ancestor of chimps and humans were bipedal, that means chimpanzees underwent an evolutionary reversal, when a species loses a recently evolved trait and goes back to the more primitive condition. In other words, it sort of “reverted” back to the non-bipedal form of gorillas and orangutans. Scientists think evolutionary reversals are rare in evolution. It is more parsimonious, as they say, to assume bipedalism only evolved in our lineage.
Comment by Erin Wayman — December 12, 2011 @ 6:17 pm
The latest evidence shows that the latest oreopithecines lived at the same time as the earliest African hominin, Sahelanthopus (6.7 to 7.1 million years ago) at a time when there was a land bridge connection between North Africa and Italy. It should also be noted that Sahelanthropus and Oreopithecus are extremely similar in their cranio-dental morphology.
Oreopithecus has 15 cranio-dental similarities with Sahelanthroups; Australopithecus has 14; Homo, 10; Pan and Gorilla, 5; Pongo, 4; and Hylobates; 3.
Comment by Marcel F. Williams — December 28, 2011 @ 1:51 pm
Disparition définitive de Homo Floresiensis 16’000 an AV JC, mais pourquoi donc?
Après 100’000 ans de refroidissement climatique, la majorité du carbone terrestre est à cette époque au fond des océans, sous forme d’hydrate de méthane, et de méthane saturant l’eau des océans. La convection du magma terrestre devient par hasard un peu plus forte: elle aspire donc les continents vers le bas et elle fait remonter le fond des océans autour du rift. Tout à coup, le rift s’ouvre sur toute sa longueur, le magma sort massivement, se répand sur le fond des océans, et vaporise l’hydrate de méthane. Un fort courant ascendant se forme au dessus du rift, et tous les océans se mettent à mousser du méthane, comme le champagne mousse du CO2. Ce qui fait monter le niveau de la mer de plusieurs Km. Arrivées en haut, les bulles de méthane flambent, vaporisant l’eau de mer. D’énormes nuages se forment sur toute la terre, provoquant des pluies diluviennes. Homo Floresiensis disparaît, noyé, mais Homo Sapiens survit. Allez maintenant sur Google Maps, en vision satellite, et introduisez, par copier-coller, les coordonnées suivantes: 39°26′ 26.26″N 44°14’5.3″E , et cliquez. Ensuite, cliquez 5 fois de suite sur +. Vous ne voyez pas ce que c’est? Cliquez sur “photos”, et cliquez sur toutes les photos! Surprise! 16 mille ans AV JC…
Comment by Jean-Francois Morf — December 29, 2011 @ 3:44 pm