On May 20 of last year, at a remarkable press conference in New York, a group of researchers announced—with much ballyhoo—that they’d found a 47-million-year-old primate fossil named Darwinius masillae (nicknamed “Ida”). Ida, the finest fossil primate in existence, was touted loudly as the missing link between the two major branches of primates, the Haplorhini (anthropoids [apes and monkeys] and tarsiers), and the Strepsirrhini (lemurs and lorises; see figure below). Concurrent with the press conference was a History Channel documentary and a book about Ida, Colin Tudge’s The Link, that proclaimed, with much heavy breathing, that Ida was, as one of the earliest primate ancestors of our own species, an earthshaking discovery (see my review of the book here).
The description of Ida was eventually published in a paper by Franzen et al. in the journal PLoS ONE, a journal that doesn’t exercise stringent scientific review of submitted papers. The reaction of both bloggers and scientists was very critical, with many pointing out that Ida didn’t look like a missing link at all, but may have been only an adapiform primate, a representative of a lineage within the Strepsirrhini that went extinct without leaving descendants. The phylogenetic analysis of the PLoS paper, they claimed, was cursory and incomplete. A later paper in Nature by Seiffert et al. cast further doubt on Ida’s status, suggesting that the features that led Ida’s discoverers to lump her with the haplorhines were convergent—that they had evolved independently in haplorhines and adapiforms and thus could not serve as evidence for Ida’s anthropoid ancestry.
Well, a paper just out in the Journal of Human Evolution, by Blythe Williams et al. (including my Chicago colleague Callum Ross), appears to drive the final nail in Ida’s coffin—at least regarding her status as a missing link between the major branches of primates. Summarizing all the evidence in a cladistic framework (combining, as Williams et al. say, “hundreds of dental, skull, limb-bone, embryological, physiological and molecular characters of living and fossil primates”), they come up with two conclusions:
1. First, the Eocene adapids (of which Ida was one) were not, as Franzen et al. implied, more closely related to anthropoid primates than to lemurs and lorises. Rather, the adapids were stem strepsirrhines that lived well after that group diverged from the haplorhines (our own ancestors).
2. Second, detailed study of Ida’s mandibles, teeth, orbit, leg bones and other traits show that she possesses no clear synapomorphies (shared derived traits) with haplorhines, but rather is clearly an adapiform. All the evidence, then (more will soon be published in Proceedings of the National Academy of Sciences) puts Ida far from the haplorhines and anthropoids, and firmly in the now-extinct adapids. Franzen’s failure to recognize this apparently rests partly on their unaccountable failure to use any fossil haplorhines in their original phylogenetic analysis.
Figure 1 from Williams et al. shows where Darwinius sits in the primate phylogeny (we’re with the crown Anthropoidea):
Science Daily gives a precis of the paper here.
Well, in science you win some and lose some, and all of us are familiar with being wrong. But it’s something else to be wrong when you’ve rushed prematurely into print, proclaiming earth-shattering conclusions from a slipshod analysis. A win for the bloggers, who called Franzen et al. out within days of their announcement.
Williams, B. A., R. F. Kay, E. C. Kirk, and C. F. Ross. 2010. Darwinius masillae is astrepsirrhine—a reply to Franzen et al. (2009). J. Human Evolution, online.
Franzen, J.L., Gingerich, P.D., Habersetzer, J., Hurum, J.H., von Koenigswald, W., Smith, B.H., 2009. Complete primate skeleton from the middle Eocene of Messelin Germany: morphology and paleobiology. PLoS ONE 4, e5723.
Erik R. Seiffert, Jonathan M. G. Perry, Elwyn L. Simons & Doug M. Boyer. 2009. Convergent evolution of anthropoid in Eocene adapiform primates. Nature 461:118-1122.