A fossil skeleton touted as a "revolutionary scientific find that will change everything" was unveiled today at a press conference in New York City. With Mayor Michael Bloomberg and filmmakers in attendance, an international team of researchers introduced the world to "Ida," the skeleton of a primate that, the team claims, may be a missing link between primitive primates and humans. But many experts aren't so enthusiastic. "It's an extraordinarily complete, wonderful specimen, but it's not telling us too much that we didn't know before," says paleoanthropologist Elwyn Simons of Duke University in Durham, North Carolina.
Researchers have been trying to trace the origins of anthropoids--a group of higher primates that include apes, monkeys, and humans--for decades. The earliest undisputed fossils of anthropoids lived in Egypt between 32 million and 35 million years ago. In the past 15 years, researchers have found older fossils, including Eosimias, that lived 45 million years ago in China and India--and most researchers argue that these diminutive fossils either are the earliest anthropoids or are their close relatives. A few researchers, however, argue instead that anthropoids arose from a more primitive group of primates--so-called adapids.
This is the view proposed by paleontologist Jørn Hurum of the Natural History Museum of the University of Oslo and paleontologist Philip Gingerich of the University of Michigan, Ann Arbor, in a paper published today in PLoS One. For the past 2 years, the two have been part of a team of scientists that has secretly studied the 47-million-year-old juvenile fossil of Ida, named for Hurum's 6-year-old daughter. The squirrel-monkey size fossil is 95% complete and remarkably preserved, including the contents of her gut when she died. Although private collectors discovered the fossil in 1983, it was split in two. They sold one half to a museum in Wyoming, and a private collector held the other half until 2 years ago, when Hurum bought it for the museum in Oslo.
Using high-resolution computed tomography scans, the team analyzed the skeleton from the Messel quarry in Messel, Germany, where it was discovered. They found features in the face, teeth, and foot that suggested to them that Ida belongs to a group of adapids known as the Cercamoniinae--and that adapids belong in the superfamily (Haplorhini) that includes anthropoids (and humans) instead of the more primitive group that includes living lemurs (Strepsirrhines), where adapids have traditionally been placed. Specifically, they argue that Ida is not on the primitive lemur line because she lacks two key characteristics shared by lemurs: a grooming claw on her second toe and front teeth arranged into a toothcomb. Also, the vertical, spatula shape of her front teeth and a bone in her ankle called the talus are shaped like members of our branch of the primates. And that means adapids are the link between primitive primates and anthropoids--and, hence, the lineage leading to humans. "This is the first link to all humans," said Hurum at the press conference.
Many paleontologists are unconvinced. They point out that Hurum and Gingerich's analysis compared 30 traits in the new fossil with primitive and higher primates when standard practice is to analyze 200 to 400 traits and to include anthropoids from Egypt and the newer fossils of Eosimias from Asia, both of which were missing from the analysis in the paper. "There is no phylogenetic analysis to support the claims, and the data is cherry-picked," says paleontologist Richard Kay, also of Duke University. Callum Ross, a paleontologist at the University of Chicago in Illinois agrees: "Their claim that this specimen should be classified as haplorhine is unsupportable in light of modern methods of classification."
Other researchers grumble that by describing the history of anthropoids as "somewhat speculatively identified lineages of isolated teeth," the PLoS paper dismisses years of new fossils. "It's like going back to 1994," says paleontologist K. Christopher Beard of the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, who has published jaw, teeth, and limb bones of Eosimias. "They've ignored 15 years of literature."