New Study Confirms That "Ida" is Not Our Great-Great-Great-Great-Etc. Grandmother

laelaps — Wed, 03 Mar 2010 07:16:49 +0000

The exceptionally preserved skeleton of Darwinius, known popularly as "Ida." From PLoS One.

Almost ten months ago an international team of researchers introduced the world to an exquisitely-preserved primate from the 47 million year old oil shales of Messel, Germany. Dubbed Darwinius masillae, and nicknamed "Ida" and "The Link", the fossil was touted as one of our earliest primate ancestors in a massive media campaign worthy of a Hollywood blockbuster. Yet the trouble was that there was no solid evidence that Darwinius was one of our ancestors. Despite the marketing blitz promoting the fossil the team of scientists who described it did not provide sufficient evidence that the lemur-like primate was anywhere close to our ancestry, and it would take the description of a related fossil primate several months later to put "Ida" in her place. Darwinius was not one of our ancient progenitors, as had been proclaimed, but instead belonged to an extinct branch of early primates which were more closely related to living lemurs and lorises.

Now another team of early primate experts has published a new analysis of the famous fossil. Writing in the Journal of Human Evolution paleontologists Blythe Williams, Richard Kay, Christopher Kirk, and Callum Ross have independently confirmed that the original description of Darwinius which appeared in the journal PLoS One was deeply flawed. Understanding why, however, requires a bit of background.

For over a century scientists have known that there are two major divisions among living primates: the haplorrhines ("dry nosed primates") and the strepsirrhines ("wet nosed primates"). The former group contains tarsiers plus anthropoid primates (monkeys and apes) while the latter is composed of lemurs, lorises, and bush babies, and independent lines of evidence have confirmed that these groups diverged tens of millions of years ago. Because of this we know that fossil primates from at least the past 55 million years must have fallen into one group or another, but the description of Darwinius aimed to throw a monkey wrench into the scientific consensus of early primate relationships.

As recognized by the scientists who described it, Darwinius was an adapiform primate which belonged to a now-extinct group of lemur-like species. Although adapiformes had once been contenders for the role of anthropoid ancestors during the 1970's and 1980's they have since been recognized as strepsirrhine primates, meaning that there was no way they could be the ancestors of monkeys (and hence apes). Despite this change, however, the authors of the Darwinius paper attempted to rehabilitate the status of adapiformes by proposing that Darwinius possessed more traits in common with haplorrhines than strepsirrhines. This would not necessarily make it one of our ancestors, but it would place it one our side of the family tree and make it more reasonable to think of it as a close relative of the earliest anthropoid primates.

This hypothesis was refuted several months later when an independent team of researchers described another 37 million year old adapiform they named Afradapis. Though not nearly as complete as Darwinius, there was enough of Afradapis to determine its relationship to other fossil primates, and the authors of the new study used this as an excuse to parse the primate evolutionary tree by comparing 360 traits across 117 living and extinct primates. Not surprisingly, the results of these comparisons were more consistent with the established consensus of early primate relationships, and the scientists ascertained that the confusion about the relationship of Darwinius to other primates may have been caused by the fact that it possessed independently evolved traits seen in later anthropoid primates (but not early ones). If you were to compare Darwinius to only living primates you might think Darwinius was a close relative of anthropoids, but the actual earliest known fossil anthropoids did not share the same features.

A simplified evolutionary tree of primate relationships showing the placement of Darwinius in relationship to other groups. From Williams et al., 2010.

The new paper by Williams, Kay, Kirk, and Ross contributes to this understanding by considering how early primates are identified as either haplorrhines and strepsirrhines. Early representatives of both groups can look awfully similar to each other and lack many of the tell-tale characteristics that can be useful in telling their living relatives apart. In order to assess the relationships of Darwinius the authors of the new study provide a rundown of tell-tale characteristics that can been seen in its skeleton and what those traits mean for its relationships to other primates.

One of the most important features in determining the place of Darwinius can be seen in the skull, or rather, it can't. Haplorrhine primates have a plate of bone behind the eye which strepsirrhines lack, and Darwinius does not appear to have this trait. And, curiously enough, Darwinius possesses a different trait that is missing in early haplorrhines. The original description of Darwinius stated that its two lower jaw bones were partially fused, but though this trait is seen in living haplorrhine primates it is not seen in early haplorrhine primates. The fusion of the lower jaws in Darwinius cannot be taken as a sign of affinity to haplorrhines because it is indicative of convergent evolution, not a close genetic relationship.

A more detailed primate family tree with Afradapis and Darwinius underlined in red. Lemurs are underlined in blue. Anthropoids are underlined in green. From Seiffert et al., 2009.

Combined with other traits from the skull, teeth, and limbs, the new analysis paints a rather damning picture of the original Darwinius study. The only way that Darwinius could be considered a haplorrhine (and thus a potential anthropoid ancestor) would be to consider it entirely out of context from other fossil primates. It was clearly a part of a radiation of strepsirrhine primates, and as the authors of the new paper conclude:

The lack of clear synapomorphies [shared derived characteristics] linking Darwinius to living and fossil haplorhines, the undisputed positive evidence
that it is an adapiform, and the detailed evidence that adapiforms are stem strepsirrhines, suggests that Darwinius has little relevance for understanding haplorhine evolution.

To some such statement might seem superfluous. After all, didn't the description of Afradapis already put Darwinius in its place months ago? Yes, but it is still important to have independent teams of researchers appraise the same data. Even though the hypotheses presented in the Afradapis paper confirmed what many scientists had suspected they still required independent confirmation, and now Williams, Kay, Kirk, and Ross have supplied it. (Plus, as shown by the dates supplied on the paper, the new study was submitted almost four months before the publication of the Afradapis paper so I certainly cannot blame the researchers for submitting a paper that came to convergent conclusions.)

What I am still waiting for, however, is a thorough analysis of the relationships of Darwinius by the team that originally described it. One of the ringleaders of the media circus surrounding the primate, paleontologist Jorn Hurum, promised that the initial description was just the first of many papers that would put Darwinius in context. To date no additional papers have appeared, and given the inadequate interpretation of Darwinius in the original paper I cannot help but wonder how Hurum and his colleagues can conceivably cast the adapiform as one of our close fossil relatives. I guess we will just have to wait and see.

Williams, B., Kay, R., Christopher Kirk, E., & Ross, C. (2010). Darwinius masillae is a strepsirrhine--a reply to Franzen et al. (2009) Journal of Human Evolution DOI: 10.1016/j.jhevol.2010.01.003

laelaps Wed, 03/03/2010 - 02:16

Tags

evolution

mammals

paleontology

Primates

I think it's really a shame that Ida was so overhyped, for it is truly an amazing specimen. I think the reason the media jumped on it so eagerly is that the public is just so obsessed with the "missing link" between humans and other primates. I think that's a real bummer, because there are so many other fascinating transitions in the fossil record. Personally, I'm much more interested in the dino-bird transition.

Important to note that nobody here is an "independent team of researchers". There are two teams, each with a cute fossil, each understanding that there is no way they can get 100% clear answers from the fossils, each pushing their own hypotheses, publishing competing papers and not revealing conflicts of interest when talking to the press. Why is Beard always interviewed as "independent expert" when he is part of one of the teams (the one which published the "paper" you are blogging about here)? He uses the cover of the media to attack Ida without revealing he is just trying to destroy competitors.

Misspelled. Baird.

@Coturnix: If his criticisms are valid and supported by the facts then is it really relevant that he is competing with them?

Bora; I used the phrase "independent team of researchers" because each of the three studies I discussed here was carried out by different groups of scientists. I felt it was important to make this distinction since the new paper by Williams et al. supports some of the hypotheses put forward by the Seiffert paper.

As for Beard, you are mistaken. He was not an author on any of the papers. He has often been consulted by the press because he is an expert on anthropoid origins (helped by his work on Eosimias) and written a popular book on the subject (Hunt for the Dawn Monkey). Your mention of him in your comment is a non sequitur since he is nowhere in the post and he was not an author on the Nature or Journal of Human Evolution papers. As far as I can tell at the time of the comment he has not even commented on this new paper yet. Your assertion that he is just using the media to attack competitors has, as far as I can see, no actual basis, and I can't help but wonder what you think the competing interests of the other research teams might be (especially since the Ida paper passed through to publication without any mention of competing interests despite heavy media involvement - it took Carl Zimmer's posts to get the paper amended).

Are there professional rivalries here? Almost certainly, especially since intense debates about anthropoid origins have been going on for the past 40 years or so. Even so, I do not believe that such professional tension undercuts the findings of the two new papers. The Journal of Human Evolution study rightly points out how considering Darwinius out of context led Frazen et al. to incorrect conclusions and the Seiffert et al. paper provided a detailed cladistic analysis that placed Darwinius as a strepsirrhine primate, not a haplorrhine. In other words, both studies presented actual data to support their phylogenetic conclusions whereas Franzen et al. did not provide sufficient evidence to support their case (which was even more prominently trumpeted in the media circus). Indeed, the Seiffert et al. paper was especially significant in that one of the authors was Elwyn Simons, a fossil primate expert who previously favored the adapiform-anthropoid connection but has since changed his mind.

We can argue about professional rivalries all we like, but the fact is that the two more recent studies supported their conclusions with solid evidence while the original Darwinius description suggested a major shift in the primate family tree without the requisite analysis. Hurum has promised that one is on the way, and I look forward to seeing it. I will certainly be glad to discuss it here when it is published.

And, since you mentioned competing interests, we should probably restate our own interests here, yes? I am a freelance science writer who wrote two commentaries for the Times about Darwinius and Afradapis (and I appeared twice on the BBC Radio 4 program "Material World" to discuss the same subject) while you work for PLoS (the company that runs PLoS One, the journal in which the initial Darwinius description appeared) as an Online Discussion Expert. I have been very critical of certain aspects of the Darwinius paper while you, as an employee of PLoS, obviously have an interest in defending the work of the company.

I am sorry if my ongoing commentary has hit a sore spot, but I do not believe that the phylogenetic conclusions of the description in PLoS One were well-supported by evidence. There have now been two independent studies by two different teams of researches that have failed to support the hypotheis of Franzen et al. Had the authors behind the initial description provided a rigorous evolutionary analysis, instead of rushing the paper due to media pressure, we might not have reason to be so frustrated. Science is a human endeavor in which personalities clash and rivalries flare up, but in this case the subsequent studies of Darwinius have so far shown that Franzen et al. were incorrect in their assessment.

Brian is correct. I am not a co-author on either of the technical papers that have appeared in the past several months that take "Ida" to task. Aside from this post, I have not commented publicly on the latest paper by Williams et al. in the Journal of Human Evolution. As far as I know, I am not part of some sordid scientific conspiracy to debunk "Ida" and/or PLoS One.

I am slightly offended that Mr. Zivkovic, who I have never met, and who has no obvious dog in this fight other than working for PLos One, would go out of his way to attack me here. Mr. Zivkovic, if you have interesting data bearing on the subject of anthropoid origins, please divulge it. Otherwise, stand down and go back to your editorial chores. And by the way, try and do a better job of the latter next time around.

Awesome post and response, Brian.

And yes, to reiterate, "independent" when referring to a source means "independent of the research group who did the study" not "independent of the debate/field". Who would the latter be? People without the knowledge to comment properly would defeat the point.

And cue the creationists who will gleefully gloat that yet another supposed human ancestor has been debunked.

Thanks Ida-hypers, thanks a lot.

[sigh.]

maybe i'm just an alien, but i am quiet sure i don't come from apes. no i'm not another racist or religious zealot, instead i derive this from the fact that evolution says we are all biologically and distantly related. i'm a real person and when i do elope with my wife she sure isn't going to be related to me.

personally i think that no one is related to each other (just a thought). one thing i'm more sure of is that there are a lot of fake people out there. when i mean fake i mean that i dont think they are real, as in not sentient; much like the animals we eat (and if I may add the crack dealer that 'accused' me for not buying his product on the bus tonight bothers me less then most of you people that think you eat beings that at one point were alive).

what i think is that there is a natural progression of animals that raised other animals. the bacteria that we so-called evolved from raised a different (more evolved) bacteria. after that the sea creature raised a more evolved sea creature. the ape a more evolved ape. all the way to current 'human' upbringing. of course in my theory these beings only raised the next subsequent being and they were of no biological relation.

i have no proof of this and it is only a thought, but it sure is better then the random bloke thinking he is related to his spouse.

I may have come out as too rough, but one need not be a co-author of a paper to be a part of a clique - and such 'membership' needs to be stated transparently.

Very nice post, Brian. You've done a great job clarifying these relationships for me (a non-specialist), which I found confusing since the publication of the first Ida paper. Thanks.

Bora;

You intimate that there is some kind of "anti-Darwinius" clique, but I do not see any evidence for that. There are too many links for me to collect here, but head on over to the Wikipedia page for Darwinius and follow the bouncing urls if you need more evidence. Numerous researchers from a number of institutions (Beard, Ross, Kay, Simons, Seiffert, Kirk, etc.) have criticized the paper, and we now have two papers by two independent teams that back up these criticisms in the technical literature.

(And, as a sidebar, at least one interview did mention Beard's work on Eosimias in the context of the Darwinius controversy.)

The unflagging defense of Darwinius (by way of asserting that this is mainly about professional rivalries) makes no sense to me. The limited phylogenetic analysis in the Franzen et al. paper (if it can be called that) was terrible and the majority of the world's top experts on early fossil primates have rightly called "Foul!" It is hard for me to believe that all these authorities form some kind of clique that are just trying to keep Darwinius down, especially since at least one team (Seiffert et al.) went out of their way to do the work that "team Darwinius" should have done in the first place. It is not as if Beard is the only one issuing criticisms, and I find it very strange that you have played up the idea that the opposition to Darwinius is due to professional rivalry and not actual science.

Surely this doesn't really detract from the importance of Ida as a find, though? She's still a primate from very early on in the evolutionary path of primates. There is still valuable information we may be able to get from study of the fossil.

STOP THE PRESSES! Competing teams of scientists try to debunk each other! Recriminations flying on the internet!

Discoverers of fossil primate insist their find is on the human side of the family tree. Discoverers of different fossil primates insist that it isn't!

Surely, this is unprecedented! Or not.

I am not defending Darwinius. As I said above, both fossils are incapable of getting us to any kind of certainty. This is not about science, but about responsible journalism. All I am asking for is transparency. Just saying "...from the competing group..." when citing the anti-Darwinius fan-group members.

Coturnix, you're correct that both fossils (I assume you mean Afradapis and Darwinius)- on their own- are equivocal. And that's exactly why it was so important that somebody place those fossils in the context of other Eocene primates, as these authors have done here.

The interpretation of Darwinius as a Strepsirrhine is dubious at best if you look at her on her own and compare her to living Streps. Placing her in the context of the rest of the fossil record makes that interpretation untenable. This is very much about the science- To someone who has no horse in this game but is familiar with the fossils, presenting the story as "competing teams" sounds an awful lot like "teaching the controversy."

Are there professional rivalries here? Almost certainly, especially since intense debates about anthropoid origins have been going on for the past 40 years or so.

"The closer you get to humans, the worse the science gets."
-- biologists' proverb

The limited phylogenetic analysis in the Franzen et al. paper (if it can be called that)

It can't. What it can be called is a failure of peer review.

Surely this doesn't really detract from the importance of Ida as a find, though? She's still a primate from very early on in the evolutionary path of primates. There is still valuable information we may be able to get from study of the fossil.

Absolutely.

Yes, despite my criticisms surrounding the interpretation of Darwinius "Ida" is truly a wonderful specimen. It is wonderful that such a complete fossil primate has been found and no doubt it will help us to understand how some fossil primates grew, moved, ate, etc. (I wrote a post about these aspects of the find shortly after the description was published.)

In fact, the two recent critiques have used Darwinius to show something that I think is really interesting. Some adapiform primates independently evolved traits seen in later anthropoids; together Darwinius and Afradapis present an interesting case of convergent evolution.

As I have said on Twitter and elsewhere, if anything positive has come out of this kerfuffle it has pushed fossil primate experts to engage with the public and contribute some new papers on anthropoid origins. Maybe a symposium or two will come out of this, too, and I have no doubt that we'll be talking about Ida for some time to come. As Hurum himself has said, it will be interesting to look back on all this 10 years from now (though I think we have different ideas about how things might look then). :)

Martin R. @ 9: Even species are just constructs; don't let the resolution of the analysis fool you -- The only "real" objects in this are individuals.

as I know, however, this has not been done and so the show sometimes selectively matches some evidence to the story they wish to tell.

is it interestin????