Reunion of fossil halves splits scientists

Palaeontologists have identified a new species of primate by putting together two halves of an unusually complete fossil, which were separated for decades by the vagaries of the fossil trade. One half of the fossil — which some media reports have been quick to label ‘the missing link’ — was even doctored by a past owner to make it look more impressive.

The relationship of the new species, Darwinius masillae, to other early primates has sparked an academic controversy, a press conference earlier today at the American Museum of Natural History and a television documentary to air next week. The lack of certain key features ally the 47-million-year-old Darwinius with early haplorrhines, the ancestors of anthropoids such as monkeys, apes and humans, write the authors. However, in the same paragraph they write, “We do not interpret Darwinius as anthropoid.”

This nuance was missing from an announcement last week made in advance of the study’s formal publication, which declared in block capitals that the find would “change everything”. The Daily Mail reported the fossil’s existence on 10 May when it announced the documentary about the find, and The Wall Street Journal followed with a 15 May story highlighting the potential for the find to stoke conflict between creationists and evolutionary scientists.
Family tree

The fossil is “mainly notable for its completeness”, says Christopher Beard, curator of the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, who was not involved in the study. In addition to the bones, the fossil contains an outline of the animal’s soft tissue, including partial impressions of its fur and digestive tract. But the authors’ interpretation of the species as a haplorrhine ancestor is less likely to meet with wide acceptance, he says. “It’s very easy to allocate this fossil to the adapiform group”, which includes ancestors to modern lemurs and lorises, Beard says.

Where the species belongs on the primate family tree is unlikely to be resolved between the publication of the study in PLoS ONE1 today and the appearance of the television documentary next week. “That’s the fundamental scientific issue that I suppose will have to be hashed out in the months ahead as more people get access to the specimen,” Beard says.

“There are four different views about the relationships between the different kinds of primates,” says Colin Tudge, an author of The Link, a book that was commissioned to accompany the documentary of the same name. Most scientists who study primate fossils from this period, the Eocene, associate adapids with modern-day lemurs, he says, which, unlike modern-day anthropoids, have wet noses and special teeth and claws used for grooming. Darwinius lacks the modern grooming features, a detail that the study authors say helps place it among the early haplorrhines but that Beard says could simply be because the specimen is older than present-day lemurs.
Fossil furore

The skeleton was found in sediments in Messel, Germany. Tudge says study author Jørn Hurum of the University of Oslo in Norway nicknamed it ‘Ida’, after his daughter. The sediments were a paratropical rain forest at the time Ida lived, but they were a failing shale mine when the site was excavated in the 1970s and 1980s. Sheets of shale containing fossils were often broken apart, report the study authors, and many such fossils appeared in private collections in subsequent years.

One half of Ida appeared in a private Wyoming museum in 1991, and an analysis by Jens Franzen of the Natural History Museum of Basel, Switzerland, revealed that the fossil contained fake parts2. The second half of Ida reportedly appeared on the open market in Germany in 2007, where Hurum purchased it on behalf of the Natural History Museum of the University of Oslo.

“Basically it looks like a road kill,” Tudge says — because the layers of sediment slowly compressed the fossil, which lay on its side at the bottom of an anoxic lake that may have periodically released methane, killing nearby animals and providing an excellent fossil record of life in the Eocene. The study authors suggest that Ida died young — perhaps just nine months old — and might have weighed 600 to 900 grams if she had grown to full size. The lack of a baculum bone, found in the male genitalia of many mammals, identifies her as a female.

Beard says that such well-preserved fossils are of great interest to the palaeontology community, particularly because this individual was young and because her gender is known. “This lets you study the growth and development of a primate that lived almost 50 million years ago.” For instance, researchers debate when primates began to show signs of sexual dimorphism — identifiable differences between males and females. “That’s commonly encountered especially among living anthropoid primates,” he says, but not among lemurs. “What we need now is we need males [from Messel] in order to get at that.”

“It’s always good to have more indications of what the soft anatomy was like,” says Beard.

“As for the who’s related to who,” says Tudge, “that’ll go on forever.”

First published by Nature News: [html] [pdf].