The Age of Omo I and Omo II from the Kibish Formation, Omo Valley, Ethiopia

Two articles in the Journal of Human Evolution reanalyze the geochronology of the Kibish Formation, in the Omo Valley, Ethiopia. One is titled, “Microstratigraphy of the Kibish hominin sites KHS and PHS, Lower Omo Valley, Ethiopia,” and the other is titled, “Sapropels and the age of hominins Omo I and II, Kibish, Ethiopia.”

Excavations of Kibish Formation between 1967–1974, yielded two very important Homo sapiens calvariae, each from different localities — Omo I which resembles modern humans and Omo II which has more primitive features. Omo I’s site was called Kamoya’s Hominid Site (KHS) after the discoverer, and about 2.6 km northwest of KHS, Omo II’s site, Paul’s Hominid Site (PHS) is located. These two were first indirectly dated to be 130,000 years old by a U-series disequilibrium analysis (a measurement of the decay of uranium into thorium over time) from layer near the Omo I site. Why Omo II wasn’t dated? I don’t know… later on I quote how Omo II’s exact location is kinda uncertain. Regardless, this date wasn’t well accepted. Richard Klein raised the possibility, in his book “The Human Career,” that Omo I and Omo II effectively sank into a older sediment layer (Member I) because the site was once a prehistoric delta.

About 40 years later, Frank Brown and Ian McDougall along with John Feagle returned to the Omo Valley and re-dated mineral crystals from volcanic tuffs where Omo I and II came from. Why? One reason is that the 160,000 year old Homo sapiens idaltu crania (BOU-VP-16/1, BOU-VP-16/2 and BOU-VP-16/5) from Herto, Ethiopia dethroned their claim to the oldest known Homo sapiens specimens. The team dated the 40Ar/39Ar feldspar crystals from pumice clasts above (Member III) and below layers (Member I) of river sediments that contained the early human bones. The argon-argon dates yielded a 195,000 year old age. They published their results in Nature, “Stratigraphic placement and age of modern humans from Kibish, Ethiopia.”

The big problem with this re-dating has been the uncertainty of whether or not they were getting crystals exactly from where the fossils came from. A National Geographic article summarized how the team estimated where the fossils came from,

“They were able to do this using National Geographic Society video footage taken during the first excavation. They also used photographs taken by Karl Butzer, a geologist currently at the University of Texas, who did the original geological studies of the site. Also helpful were hand-drawn maps from the late Paul Abell, another member of the 1967 team.”

As you can imagine, a substantial amount of erosion and deformation can happen to geological formations during 40 years, that would alter the stratigraphic context. And looking at videos, and photos, and hand-drawn maps is an hardly exact science. Believe me, exactly 1 year ago I was trying to find a locality based off of hand-drawn maps and missed. Frank Brown was even quoted in this same National Geographic article saying that the original locations have been lost. But they were able to find more of Omo I, including part of the femur that fit a piece found in 1967.

In the two new papers, both sets of authors reanalyze the best available evidence to pinpoint where Omo I and II came from: Member 1 of the Kibish Formation. Craig Feibel reconstructs the microstratigraphy of the formation and writes that he cannot falsify Klein’s claim but reaffirms that,

“The documented abundance of vertebrate fossils deriving from restricted levels in upper Member I provides an accumulational/preservational context within which the hominins are not out of place. Intrusion during the short period of terminal delta-plain development in latest Member I times would be temporally insignificant in any case.”

McDougall, Brown and Fleagle return to the argon-argon dating. They turn to checking out alkali feldspar crystals in pumice clasts and figure out that Nakaa’kire Tuff in Member I, and directly below the hominin levels, is 198,000 years old — extending the age of Omo I and II by 3,000 years. I do not know why PHS was not dated, but in the new paper the authors do write that the site of Omo II was mislocated by Butzer in his maps. In their conclusion, they make a snarky/competitive comment to the Herto discoverers, saying,

“Thus, the hominin fossils from Kibish are about 40 ka older than those from Herto, making Omo I and Omo II the oldest well-dated anatomically modern human fossils yet recovered.”

    FEIBEL, C. (2008). Microstratigraphy of the Kibish hominin sites KHS and PHS, Lower Omo Valley, Ethiopia. Journal of Human Evolution DOI: 10.1016/j.jhevol.2008.05.011
    MCDOUGALL, I., BROWN, F., FLEAGLE, J. (2008). Sapropels and the age of hominins Omo I and II, Kibish, Ethiopia. Journal of Human Evolution DOI: 10.1016/j.jhevol.2008.05.012
    McDougall, I., Brown, F.H., Fleagle, J.G. (2005). Stratigraphic placement and age of modern humans from Kibish, Ethiopia. Nature, 433(7027), 733-736. DOI: 10.1038/nature03258

21 thoughts on “The Age of Omo I and Omo II from the Kibish Formation, Omo Valley, Ethiopia

  1. Regardless of the dating (let’s say between 150,000 and 200,000 years old?) I have always found the most interesting thing about the specimens is, “Omo I which resembles modern humans and Omo II which has more primitive features”.

    Now we continually hear that modern-looking humans appeared around that time (mitochondrial Eve anyway). And we are also told often enough that these modern-looking humans didn’t breed with archaic-looking ones. Does this mean that Omo I and Omo II belong to different species? (I’m not really serious).

  2. Never mind that, the important question is how robust were their toes (I’m not really serious either).

  3. “Hominin” or plainly “human”?

    Whatever Terry says above, both look human (H. sapiens) to me, even if it’s difficult to evaluate from just the upper piece of the skull. Omo 2 shape actually resembles Upper Cave 101, while Omo 1 looks more mesocephalic, what is quite interesting for an African skull.

  4. Well, Homo Antecessor is at least 850, ooo years old and it certainly is a much more modern anatomically modern human than is either one of these ! So, why do they say “human” when for Antecessor they say, pre-modern? You tell me!

  5. Hal,

    The current consensus understands H. antecessor to be either the same species or a direct antecedent to Homo heidelbergensis. It is suggested that this is the last common ancestor of Homo neanderthalensis and Homo sapiens.

    I don’t know on what basis you’re considering H. antecessor more anatomically modern than these fossils… Can you please explain?

    Kambiz

  6. I wonder…have these researchers developed a method for tracking the iron content of fossils?

    In my limited understanding, all things eventually turn into iron and one of the things that happens to fossils is that they deteriorate and leave iron behind.

  7. Maggie,

    You’re wrong. All things do not turn into iron. Atoms do, however, decay, throughout time…

    Are you thinking that carbon atoms (who have six protons and six electrons) turn into iron atoms? Because, that can’t happen unless some sort of nuclear fusion occurs. Nuclear fusion occurs naturally in stars, and in atomic bombs. It doesn’t just happens as fossils deteriorate…

    Kambiz

  8. Kambiz ! I kn0w what they say – but Homo Antecessor has a completely human face ! He is absolutely a modern human. No pre-modern has a flat face – yet they say this guy predated Neanderthals! What nonesense! The evidence they have against what I say is very slight – brow ridges toward the side of the head and a few teeth with the same number of roots as Australopithecus – I was not born yesterday, there are many modern humans with the same features – no, if bones can tell you anything at all it hast to be that Homo Antecessor is an anatomically modern human – check it out!

  9. Boy, you’re enthusiastic about Homo antecessor being considered modern.

    While the midfacial topography does shows a fully modern pattern, there are many more ‘primitive traits.’ For example, the body of the teeth and pulp chamber are enlarged, which is seen in H. erectus and H. heidelbergensis. The dimension of the I2 also resemble H. heidelbergensis.

    The most glarring difference is that the average brain volume of Homo antecessor was 1000 cm³. Some specimens show a volume of 1150 cm³. Modern humans are 1350 cm³. If we consider big brains characteristic of modern humans, which we do… then H. antecessor was not modern.

    Other features acquired seen in H. antecessor are protruding occipital bun, a low forehead and a lack of a chin. Taking in all these primitive traits into mind, the smaller brain, the large teeth, and these features in the skull — they outweigh the modern looking face. For that reason, H. antecessor is not considered to be modern.

    Kambiz

  10. I understand that the exact cranial capacity of H. antecessor is somewhat in doubt, but even so, it is still within the modern range – for example, consider the sex of the skull – if female, than the range is again normal – as for the 1000c.c.’s, well, the whole skull is not there and I suspect that the people who hold the H. antecessor bones tightly hostage to their point of view (come-on, how could H. Antecessor be the ancestor of Neanderthals? We used to look human then we grew a huge heavy mussel?). Look at the muscle inserts on H. Antecessor, perfectly human! Look at the muscle inserts for Neanderthal – same deep pits as you find in a gorilla exactly! No, the only reason for believing Antecessor is not modern is his age – otherwise no one would take the finders and wardens theories of the million dollar bones seriously. There is enough evidence and science to indicate that H. Antecessor had a perfectly normal brain size. All they have on their side is the million year age of her.

  11. you said: ” Other features acquired seen in H. antecessor are protruding occipital bun, a low forehead and a lack of a chin. Taking in all these primitive traits into mind, the smaller brain, the large teeth, and these features in the skull”- the thing is not modern human, but I say, * the ‘bun’ is perfectly within modern context – not like the Neanderthal bun – the forehead is low, but within the normal range – and it has a chin and it is well within the normal range (lots of us have receding chins worse than his)
    His teeth are not that remarkable at all – I bet you would find that 20 % of us have teeth of the same size – it is not fair to divorce this guy just cuz he was ugly. If it barks like a dog… If it has a face exactly like a modern human, then, by God, it certainly is a modern human and must remain so in our minds until such time as they discover (as with Neanderthals) to the contrary. There never, ever has been found a hominid with a flat modern face that was not an anatomically modern human, ever! Until they told this falsehood about H antecessor – Neanderthals have lots and lots of bone characteristics that branded them in the mind of many as not being of our species – not at all so with the one they are accusing of being the forbearers of Neanderthals !

  12. Well, no answer is forthcoming from you, sadly: So, let me end this string by pointedly pointing out once again that Homo Antecessor is the only hominid to possess a completely human FACE! The only one EVER! Now, to explain this explosive fact away, the (now exceedingly rich) wardens of the million dollar bones nitpick on very slight deviations from the norm found on those million year old bones – deviations that are also fairly commonly found in all modern human population even today [come on! Homo Antecessor is a million years old! Dahhh! What’s you expect?] Here is what they are saying to explain the million years which disproved the “out of Africa theory” – once we humans, or some people who looked exactly like us (the only ones) lived in Europe, and then we changed into a heavy faced sub-human with the animal strength of ten anatomically modern humans – and many, many other very important anatomical differences that make it clear that NEANDERTHALS HAVE NOT BEEN US FOR AT LEAST FOUR MILLION YEARS! It is only wishful thinking and magic that makes you think that WE are the ancestors of the damned Neanderthals!

  13. Hal,

    You’ve made it clear that you’re a troll, and looking to pick a fight — not have a discussion. I really don’t think you know what you’re talking about. Neandertals haven’t been around for 4 million years to be us.

    Kambiz

  14. yeah! and then we evolved back into people who look like us again – yeah, sure, I believe you.., but really, how likely is THAT?

  15. excuse me, I should have said that subjects most closely resembling those heavy-faced hominids have been around for four million years or so.

  16. why in the world would I be a troll on a subject like anthropology? Whose interests could I possibly be serving? And why?

  17. Why, thank you alex, but of course the idea of a scientific geek troll is hard to picture – but perhaps he meant to say something else, or maybe I don’t know exactly what a “troll” is?

  18. Hal,

    Based off of your commentary in this thread, you are an Internet Troll. You may think that Homo antecessor is ‘on-topic.’ But, this species was not a part of the original discussion. You felt the need to interject your opinions in an inflammatory manner and drive the discussion off the topic at hand, and that is the age of the Omo fossils.

    Kambiz

  19. Well, I never looked at it that way, but I certainly do not want to be a troll, so I will stop talking about Homo Antecessor

  20. “John Feagle returned to the Omo Valley and re-dated mineral crystals from volcanic tuffs where Omo I and II came from. Why? One reason is that the 160,000 year old Homo sapiens idaltu crania (BOU-VP-16/1, BOU-VP-16/2 and BOU-VP-16/5) from Herto, Ethiopia dethroned their claim to the oldest known Homo sapiens specimens.” I merely begged to differ, but, there are things a “troll” may not bring up on a site like this, or horrible things might happen! So, what can I do but respect that? Death is better’n to be a “Troll”!

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