By Brandon Keim October 21, 2009 | 1:42 pm | Categories: Anthropology
Originally promoted as the stem of the primate family tree, it now appears that Darwinius masillae — better known as “Ida,” the fossil that “changes everything” — belonged to a fringe branch.
This is the conclusion of researchers who analyzed primate fossils to determine where their own discovery, dubbed Afradapis and closely related to Darwinius, belongs on the tree. Far from spawning the ancestors of humans, the 47 million-year-old Darwinius seems merely to have gone extinct, leaving no descendants.
“It’s the first phylogenetic analysis of this important animal,” said study co-author Jonathan Perry, a Midwestern University paleoanthropologist. “By our analysis, the taxon Darwinius does not appear to be” at the root of all simians, said Perry. “It’s on the opposite side of the tree.”
The analysis of Perry’s team, published Wednesday in Nature, would likely be of purely academic interest had Darwinius been introduced according to paleontological custom. That would have been in carefully written papers presented for review to the scientific community, who already had some informal familiarity with the research. But that’s precisely what didn’t happen.
Known from a single specimen purchased by the University of Oslo from a private fossil collector and studied in total secrecy, Darwinius was announced to the world at a May press conference featuring New York City mayor Michael Bloomberg. The scientific article describing Darwinius, published in PLoS ONE, came after the TV special and book, both entitled The Link.
“This is the first link to all humans,” said Jørn Hurum, a member of the Darwinius team, at the press conference. His colleague Jens Franzen likened its scientific impact to “an asteroid falling down to Earth.” Hurum said the fossil, named “Ida” in honor of his daughter, would be a paleontological “Mona Lisa for the next 100 years.” Ida was front-page news; Google celebrated it with an iconic logo cartoon. The only people unimpressed by their conclusions were scientists.
As prominent paleontologists soon pointed out, Hurum’s team was pushing a theory that most researchers had already dismissed, that anthropoids — monkeys and apes, including ourselves — are descended from lemur-like members of a primate subfamily called adapids, of which Darwinius was one.
According to Hurum’s team, Darwinius possessed many of the physical traits expected in the earliest ancestral anthropoid, so it must be that ancestor. And since Darwinius was clearly an adapid, then adapids were at the root of the anthropoids. But their paper made no reference to extensive fossil and genetic evidence suggesting otherwise.
At the time, asked by The New York Times about his team’s promotion, Hurum said that “any pop band is doing the same thing,” and that “we have to start thinking the same way in science.” Contacted by e-mail about the Nature study, he said, “At last the scientific discussion starts!”
The Nature paper marks the debut of another adapiform, called Afradapis and known from a handful of fossil teeth and jawbone fragments gathered over the last several years in Egypt.To better understand Afradapis’ place in the primate narrative, Perry’s team studied fossil measurements gathered from 117 living and extinct primate species. In what’s known as a cladistic analysis, they ran the measurements through a computer program that determined the most likely evolutionary configuration of the species.
No such analysis was performed by Hurum’s team on Darwinius. And according to Perry’s cladistics, both Darwinius and Afradapis are located where conventional wisdom expected them to be — on an early twig of the branch that produced lemurs, and far from the lineage that spawned monkeys and great apes.
The study “is spot-on in its interpretation of the phylogenetic position of Darwinius,” said Richard Kay, a Duke University evolutionary anthropologist whose review of The Link was entitled, “Much Hype and Many Errors.”
Christopher Beard, a Carnegie Museum of Natural History paleontologist who originally called Darwinius “a third cousin twice removed,” also agreed with the Nature results. Darwinius “is only very distantly related to living and fossil anthropoids,” said Beard.
Hurum retorted that “there’s a lot of ways to do cladistics,” and said the Nature authors used only some of their Darwinius measurements, ostensibly omitting those that might have provided a different evolutionary narrative.
Philip Gingerich, a University of Michigan paleontologist and member of the Darwinius team, said the Nature team’s explanation of Afradapis was “implausible,” given how much it looks like a monkey — and Darwinius looks even more monkey-like.
This back-and-forth is typical of science and especially paleoanthropology, a research field predicated on competing interpretations of tiny bone fragments. It’s also the sort of dialogue that was missing from Darwinius’ overhyped debut.
“Ultimately it’s about science, and how sound the science is,” said Perry.
Images:
1. Darwinius masillae, from PLoS ONE.
2. The adapiform branch of the primate family tree, from Nature. D. masillae is highlighted, and located beside Afradapis; the great apes, including humans, trace their origins to the stem and crown Anthropoidea.
+++++
Source/Fonte.
