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New ape fossil challenges DNA evidence about ancient split from other primates

The views expressed are those of the author and are not necessarily those of Scientific American.


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primate skull found that might illuminate human and great ape evolutionWith high-speed DNA sequencing, scientists can look at slight genetic differences among humans, great apes and other primates to arrive at new estimates of when different ancestral groups split.

These findings provide invaluable insights into the evolutionary past, especially when the fossil record is sparse, as it is for the period when the ancestors of humans and great apes split from the Cercopithecoidea (or Old World monkey) lineage tens of millions of years ago.

DNA analysis has pegged this split some 35 million to 30 million years ago, but a new fossil specimen challenges that molecular data with rock-hard evidence.

The partial skull of an ancient primate, dubbed Saadanius hijazensis, seems to have trappings of both the Hominoidea and Cercopithecoidea lines. A group of researchers led by Iyad Zalmout of the Museum of Paleontology at the University of Michigan asserts that S. hijazensis is a catarrhine—a member of the common group before the two lineages split. The primate has been dated to the Oligocene between 29 million and 28 million years ago—indicating that the split between Old World monkeys and the ancestors of humans and great apes occurred more recently than genetic evidence has suggested.

The researchers used micro-computed tomography to scan the fossil fragments and compare the clues to other known ancestral great apes and Old World monkeys.

The skull belonged a male, weighing some 15 to 20 kilograms, with a "snout-like projection of the midface," and was found in a black-mangrove environment in what is now Saudi Arabia. The study was published online July 14 in Nature (Scientific American is part of Nature Publishing Group).

Although this ancient fragment cannot fill in all of the blanks in the human evolutionary tree, new primate species finds in this common, catarrhine line "are crucial for providing a method for recognizing basal hominoids," the authors concluded.

Image of cranium, found in 2009, courtesy of Iyad Zalmout/University of Michigan Museum of Paleontology





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  1. 1. BillR 6:42 pm 07/14/2010

    Why is it that everyone assumes that there is a clean break at each branch in the evolutionary tree? The original lineage can continue past any branching for quite some time before becoming extinct. The branching event(s) themselves would not result in the extinction or end of a line, other factors would.

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  2. 2. jtdwyer 7:48 pm 07/14/2010

    BillR – My thought exactly. While this new evidence indicates that a more ‘primitive’ line continued to exist later than previously thought, it does not preclude the earlier development of more ‘modern’ lines.

    An absence of fossils is not evidence of extinction. Since fossilization occurs only in special environment conditions at death, fossil samples do not necessarily provide a statistically valid representations of populations existing during past times. As I understand, droughts flooding conditions significantly effect fossil production.

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  3. 3. robert schmidt 8:19 pm 07/14/2010

    @BillR, as far as I know you are the only one who has mentioned anything about a "clean break" as a result of extinction. The primary driver of speciation is geographical separation not extinction. Ultimately anything that prevents two gene pools from mixing will result in speciation. Time can be another driver. For example; a modern species would have decreasing reproductive success breeding with members of its lineage the further back in time you went. This is not due to a speciation "event" but rather the accumulation over time of genetic changes that make the genomes incompatible. Though you could say the ancient holotype is currently extinct you would not be able to point to a moment in time where the one species became extinct and the other emerged. This is something that confuses people. Many people seem to believe that in a single generation a new species is born with completely new traits. The fact is if you compared every organism today to its parents, and its parents to their parents and so on you would see very little difference from one generation to the next all the way back to our common ancestor. It is the accumulation of changes over time and then comparing two distantly related organisms to one another that gives the appearance of abrupt change. And because fossilization is a rare event, and rarer still is the happy accident of finding a fossil, we don’t have many "intermediaries" to show that gradual change. One way to think of it is like watching a child grow. From one day to the next they look the same. You couldn’t point to a single day in which they physically changed from a child to an adult. But if you weren’t able to see them on a daily basis but instead compared photos taken months and years apart you would suddenly see drastic changes and would likely be able to group the pictures as child, teenager and adult.

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  4. 4. jtdwyer 9:10 pm 07/14/2010

    The article states:

    "DNA analysis has pegged this split some 35 million to 30 million years ago, but a new fossil specimen challenges that molecular data with rock-hard evidence."

    "The partial skull of an ancient primate, dubbed Saadanius hijazensis, seems to have trappings of both the Hominoidea and Cercopithecoidea lines. A group of researchers led by Iyad Zalmout of the Museum of Paleontology at the University of Michigan asserts that S. hijazensis is a catarrhine–a member of the common group before the two lineages split. The primate has been dated to the Oligocene between 29 million and 28 million years ago–indicating that the split between Old World monkeys and the ancestors of humans and great apes occurred more recently than genetic evidence has suggested. "

    The article indicates that a split between Old World monkeys and the ancestors of humans and great apes occurred. It also indicates that DNA analysis had indicated that the split occurred 30-35mya, but the discovery of a fossil with both ‘primitive’ and ‘modern’ characteristics dated to 28-29mya is considered to indicate that the (decisive) "split" occurred later.

    BillR – I think you understood the article correctly.

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  5. 5. robert schmidt 9:47 pm 07/14/2010

    @jtdwyer, yes a split did occur but not because one went extinct and the other didn’t. Clearly old world monkey’s still exist. The point of the article is that an animal with traits from both lineages is more modern than originally thought. Does this represent a third line that went extinct? Potentially, but if so it would also have traits not represented in either the hominid or old world monkey lineages. So, the split must of happened fairly close in time to when this organism lived. Keep in mind we aren’t talking about a few years here, were talking about time periods long enough for organisms to evolve significant differences in their phenotypes.

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  6. 6. jtdwyer 10:34 pm 07/14/2010

    robert schmidt – The article mad no mention of any absence of "traits not represented in either the hominid or old world monkey lineages" indicating that "the split must of happened fairly close in time to when this organism lived."

    I think your supposition goes to the heart of BillR & my objections to the article: it seems to indicate that the discovered fossil represents a common precursor to both modern humans and Old World monkeys. Keep in mind that you are not lecturing to an audience of ancient morons – it’s very tiresome.

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  7. 7. deuron 7:02 am 07/15/2010

    -"The primate has been dated to the Oligocene between 29 million and 28 million years
    agoindicating that the split between Old World monkeys and the ancestors of humans
    and great apes occurred more recently than genetic evidence has suggested."-

    The above statement seems to be a conclusion. Is it stated or shown anywhere in this
    article, that the split could not have occurred before the extinction of "Saadanius
    hijazensis"? It is an interesting find but, "Saadanius hijazensis" could have existed
    for several million years before this particular creature died. I’m not seeing
    sufficient information in this article to support the above conclusion, perhaps it was
    accidently omitted.

    I’m not trying to defend DNA analysis as an absolute measure either but, the title
    indicates that this find challenges its accuracy. I don’t see it. I admit the title
    is provocative (it made me read it).

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  8. 8. Johnay 11:05 am 07/15/2010

    How long ago did horses and donkeys split? Perhaps this individual was a primate "mule".

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  9. 9. robert schmidt 12:56 am 07/16/2010

    @jtdwyer, "The article mad no mention of any absence of "traits not represented in either the hominid or old world monkey lineages"" it also didn’t indicate that there were any so unless you have some evidence that was not presented in the article you are inventing facts to support a hypothesis based on ignorance. That is tiresome. Furthermore the article states that the creature had a mix of both old world monkey and great ape traits. If the split had happened when originally thought the traits may have been weighted more towards great apes than monkeys. 5 mya is a long time.

    The fact is, this isn’t a scientific paper, it is five paragraphs long for shyte sakes. It is a news article. It is true that there isn’t enough information here to claim the findings as definitive but there also isn’t enough information for anyone to be critical of the findings. It is ridiculous to invent evidence or use the lack of detail in the article as evidence that the findings are unjustified. You have even less to support your claims than the author of the article. But if you care that much about it, read the actual peer reviewed paper when it comes out, then do your own research and publish your rebuttal, if you still disagree.

    "you are not lecturing to an audience of ancient morons", you haven’t convinced me of that.

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  10. 10. jtdwyer 10:35 am 07/16/2010

    robert schmidt – Reader comments require even less support than a news article. It seems you hold readers’ comments to a higher standard than to the articles posted on the Scientific American website. I disagree, and am still free to criticize the professional journalists and scientists on the content of their reports as a means to improve them. Perhaps you feel some need to improve the quality of my comments?

    You first argued:
    "Does this represent a third line that went extinct? Potentially, but if so it would also have traits not represented in either the hominid or old world monkey lineages. So, the split must of happened fairly close in time to when this organism lived."

    Now you accuse me of inventing evidence, stating that:
    "Furthermore the article states that the creature had a mix of both old world monkey and great ape traits. If the split had happened when originally thought the traits may have been weighted more towards great apes than monkeys. 5 mya is a long time."

    Will this evidence be published in your paper on the subject?

    Its apparent that you are convinced that you are the smartest person in the room. Enjoy yourself.

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  11. 11. deuron 11:41 am 07/16/2010

    The article implies "clean break" as BillR stated in the first comment.
    It’s hard to ignore. It’s the elephant in the room.
    The article does not contain the logic to support its conclusion.

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  12. 12. robert schmidt 11:42 am 07/16/2010

    @jtdwyer, "Reader comments require even less support than a news article." the rules of logic apply to all people. No one gets a pass. "I disagree, and am still free to criticize the professional journalists and scientists on the content of their reports as a means to improve them." you are free to write and say whatever you like, just as I am free to call you out if you make erroneous statements.

    You will notice my comments were not phrased as absolute statements of fact rather more as considerations why the authors of the article came to the conclusions they did. My conclusions were based on the evidence presented in the article as well as the conclusions of the authors. Your conclusions required the existence of evidence that was not in the article and of which the authors were either intentionally or unintentionally unaware. Again, there was no justification for your conclusions.

    "Will this evidence be published in your paper on the subject?", I don’t need to write a paper as I don’t disagree with the findings of this one.

    "It’s apparent that you are convinced that you are the smartest person in the room" sorry, but being smarter than you doesn’t make me the smartest person in the room. Fact is, I am not the one claiming to know more than the people who have actually done the field work and dedicated their professional life to the subject, based on nothing more than five paragraphs of summary. Clearly you think you are not only smarter than anyone else posting comments at sciam but smarter than the scientists posting the articles. That takes some arrogance.

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  13. 13. robert schmidt 11:54 am 07/16/2010

    @deuron, as I stated, the purpose of the article, as with most articles at sciam, is not to present the case for the author’s conclusions, rather it is there to inform people of the discovery and author’s impressions. It is a news article! If you want a technical document that presents the entire case then you need to read the scientific paper(s) that come from this. The Nature journals cover discoveries in that level of detail, not sciam.

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  14. 14. jtdwyer 4:07 pm 07/16/2010

    robert schmidt – The suthors of Scientific American articles do not need to be defended by your attacks on readers’ comments. That other readers wish to comment about the articles may indicate that they are not meeting their informational requirements. If any article, news or other reports, does not clearly and effectively communicate to its readers the authors and editors should be informed. Even a simple news article should not convey information that is misleading or easily misinterpreted.

    It is a reader’s comment! This Scientific American, which has for many decades been directed to a more general audience than Science or Nature, which are intended for scientists. If you require that all readers comments be ‘peer reviewed’ perhaps you should only read Nature.

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  15. 15. robert schmidt 8:42 pm 07/16/2010

    @jtdwyer, your hypocrisy is sad yet funny. You think that making irrational criticisms of others is well within your rights but whine about how you’ve been wronged when others criticize you. Nowhere did I state that people’s comments needed to be peer reviewed. That is just another reductio ad absurdum from the master. People aren’t even required to be rational but if they aren’t I may call them on it, just as I would expect others to call me on it when I’m wrong. Unlike yourself, I don’t need to have my delusions validated. I’d rather know the truth even if it means discarding a cherished belief.

    "Even a simple news article should not convey information that is misleading or easily misinterpreted." the arrogance, once again you assume that because you don’t understand something it’s sciam’s fault. Your misinterpretation was all your own doing. There was no information in the article to support your claim. You need to understand that it is very challenging for sciam to anticipate the extremely creative ways you have of misunderstanding a simple summary. Obviously the world needs to work harder at accommodating your special needs.

    "been directed to a more general audience" yes! And that means that they do not go into the level of detail required to prove their hypothesis. You can’t have it both ways. You want a detailed analysis so you can’t misinterpret it and a pop-up book so you can understand it. I think you need to come to terms with your own limitations. You need to understand that the reason you don’t get it is because YOU don’t understand it. It is not anyone else’s fault.

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  16. 16. jtdwyer 9:00 pm 07/16/2010

    robert schmidt – You suggested that if I did not agree with this article I should read the scientific paper when it became available and, if I did not agree with their findings I should publish a rebuttal in a peer reviewed scientific journal. This absurd procedure would effectively prevent any readers from making any disagreeable comments. No, thanks, Mr. Wizard.

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  17. 17. robert schmidt 9:54 pm 07/16/2010

    @jtdwyer, I stated that if you care enough about it then that’s what you should do. I didn’t state it as a requirement. It seems obvious to me that if you have such an absolute grasp of the subject matter that you are able to make unquestionable, authoritative rulings on the validity of the article then you should share your knowledge with the world rather than wasting it on a "comment". That is what I would do. Clearly there is no doubt in your mind that you are right and the scientists are wrong. So why keep the world in the dark? Share your gift of insight with the rest of us poor folk who have to draw our knowledge from tedious experimentation and fancy book learnin’. Or are you just full of crap?

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  18. 18. tichead 11:30 pm 07/16/2010

    Riighht… So, when you all get over shootin’ spitballs at each other in the back of the class…

    My take away on this is that the DNA time sequencing is still somewhat fungible. The scientists are still working out the tuning on DNA dating. The fossil record, sparse as it is, helps to refine the DNA clock. Therefore, whenever scientists have a fossil that can calibrate the DNA clock more accurately, especialy within 10% of the MYA (as in MILLIONS of years before you and me took our first breath and will take our last *), then I would consider progress has been made.

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  19. 19. jtdwyer 9:59 am 07/17/2010

    As I understand them, here are the essential facts as portrayed by this article:

    - The family Hominidae consists of chimpanzees, gorillas, humans and orangutans, collectively known as the great apes.

    - Cercopithecoidea is the family of old world monkeys.

    - DNA analyses had indicated that the two families had split 30-35 million years ago.

    - A new fossil, dated to 28-29Mya, has been discovered that is said to have `trappings’ of both the Hominoidea and Cercopithecoidea lines.

    - A research group asserts that the new species is a catarrhine–a member of the common group before the two lineages split, indicateing that the two families split less than 28-29Mya.

    I suggest that the Hominoidea and Cercopithecoidea families could have split 30-35 million years ago even though a catarrhine species could have survived beyond that date. This is a simple alternative to the research group’s conclusion. To disprove this alternative would require that no Hominoidea and Cercopithecoidea lines existed prior to 28-29Mya. The absence of fossil evidence of Hominoidea and Cercopithecoidea lines would not disprove this alternative.

    However, I have no qualifications to question a report of unpublished research with simple, straightforward reasoning. The research group may have some evidence not mentioned in this report: perhaps I should not question this report until the research is presumedly someday completed and published, even if other experts in this field may never adopt this small group’s conclusion, which often occurs with fields of research. On the other hand, perhaps this report of an unsubstantiated assertion should not have been posted by Scientific American until the research had at least been completed so that it could be adequately described.

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  20. 20. tichead 1:49 pm 07/17/2010

    Well stated. I agree.

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  21. 21. JamesDavis 4:43 pm 07/20/2010

    While all you great philosophers engage in elementary discussions, I’ll break the good news to you….

    We modern humans mysteriously appeared on this planet about 60 to 75 thousand years ago. We cannot be carbon-dated past that point. Because of our advanced weapons and hunting skills, we caused the Neanderthal to migrate back toward the land masses of the southern hemisphere – modern Australia and Africa; where there was more food available and less competition for it.

    If you check out some of the findings in the Northern Hemisphere, you will see that the humans made impossible and incredible advancements over their neighbors the Neanderthals. In the last hundred years, the humans in the Northern Hemisphere went from riding horsed to landing on Mars, while the Neanderthals in the far Southern Hemisphere are still basically living in straw huts and chucking spears at each other. I am not being unrealistic, I am stating a fact. Open your mind and eyes and understand.

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  22. 22. jameszaworski 5:55 am 08/21/2010

    The "molecular clock", or postulate that mutations occur at a predictable and measurable rate, is not precise. The rate of mutation is variable, and not predictable and can be rapid or slow. Doesn’t anyone remember punctuated equilibrium?

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  23. 23. jtdwyer 6:30 am 08/21/2010

    jameszaworski – I think, or really, guess, that the relatively smooth rate of mutations applies only to seemingly random changes to genetic sequences, most of which are not expressed.

    Discernable expressions of genetic characteristics occur more sporadically…

    Link to this

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