Ida has several characteristics shared by humans such as an opposable thumb, relatively short arms and legs, and forward facing eyes. But she may not have been on the same branch of our family tree, says a new study.
Credit: The Link
SYDNEY: Earlier this year a fantastically preserved 47-million-year-old primate, was the subject of a heated debate. But a new study says it can’t possibly be an ancestor of humans.
Erik Seiffert, and his team, did an extensive analysis, detailed in the British journal Nature this week, which looking at 360 anatomical features of 117 living and extinct primates.
They also took a closer look at the jaw and teeth of a newly discovered 37-million-year-old Eocene primate from Africa, named Afradapis – a relative of Darwinius, the species at the centre of the controversy.
“Our analysis of early primate relationships is the largest that has ever been undertaken, and our results indicate that Afradapis and Darwinius played no role in the origin of higher primates,” said Seiffert, an anatomist at Stony Brook University, in New York, USA.
Largest yet study
The controversy began when a team led by Jørn Hurum, from the Natural History Museum in Oslo, Norway, published a paper in May 2009 which described the discovery of Darwinius masillae, an early primate they dubbed 'Ida' (see ”Astounding primate fossil excites experts”).
Their analysis placed her in a category alongside the ancestors of monkeys, apes and humans, on the basis that she had primitive features that were similar to those species. These traits included a monkey-like jaw, spatula shaped teeth, a short face and a steeper ankle joint.
The press machine surrounding the announcement – which simultaneously released a book and a DVD narrated by David Attenborough – referred to Ida as a ‘missing link’ in the early history of primates – an idea which some experts discounted as conjecture.
Convergent evolution
Seiffert said his new data suggests that Ida and her close relatives (the adapiforms) are instead part of the 'strepsirrhine' sister group to monkeys and apes, which includes modern lemurs.
“Our analysis indicates that adapiforms were the first African primates to show the specialised tooth and jaw features that are seen in living anthropoids [monkey, apes and humans],” Seiffert said.
According to him, however, these similarities found in Darwinius and Afradapis developed coincidentally in a process known as convergent evolution.
Jonathan Perry, an anatomist from Midwestern University, and co-author on Seiffert’s paper, added that the traits seen in these species appear to be more complex than some found in apes that appeared later. This suggests that they may have developed the similarities simply because they shared the same eating habits, he said.
Hurum told Cosmos Online that he is not convinced by the new study. The Afradapis fossil is incomplete, mostly made up of a lower jaw, and is 10 million years younger than Darwinius, he said, limiting the extrapolations that can be made from it.
He also argued that Seiffert and his team selectively chose aspects of his original description of Ida, while ignoring others.
Though many of the more primitive primates from the Eocene have no descendants, and some lived at the same time as the earliest monkeys and apes, “this does not exclude at least some of them from being members of the stem group from which all higher primates evolved,” said Hurum.
Debate continues
Chris Beard, curator of vertebrate palaeontology at the Carnegie Museum of Natural History in Pittsburgh, U.S., was initially sceptical at the suggestion that Ida was a missing link. He commented that “[the new analysis] confirms my views. Ida is about as far away from the anthropoid lineage as one can get and still be a primate.”
“It is really the first thorough and systematic analysis of where the fossil primate skeleton known as Ida fits on the family tree of living and fossil primates,” added Beard.
Hurum said that his team, are currently in the process of high-resolution CT scanning to gain a clearer understanding of Ida’s hand and feet morphology. He believes that the steeper ankle joint is an important feature that needs to be taken into consideration, instead of focusing on similarities and differences of the jaw and teeth alone.
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