Omo skulls redated

[Martin Davison]

I just noticed this interesting report:

http://news.bbc.co.uk/1/hi/sci/tech/4269299.stm

Martin

[Daryl Habel]

I just noticed this interesting report:

http://news.bbc.co.uk/1/hi/sci/tech/4269299.stm

Martin

Thanks Martin,

The paper is published in this week's Nature, at:
ACCESS HERE.  The abstract (below):
 

Nature 433, 733 - 736 (17 February 2005); doi:10.1038/nature03258  
 
Stratigraphic placement and age of modern humans from Kibish, Ethiopia

IAN MCDOUGALL1, FRANCIS H. BROWN2 & JOHN G. FLEAGLE3

1 Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
2 Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA
3 Department of Anatomical Science, Stony Brook University, Stony Brook, New York 11794, USA

Correspondence and requests for materials should be addressed to I.McD (ian.mcdougall@anu.edu.au).

In 1967 the Kibish Formation in southern Ethiopia yielded hominid cranial remains identified as early anatomically modern humans, assigned to Homo sapiens. However, the provenance and age of the fossils have been much debated. Here we confirm that the Omo I and Omo II hominid fossils are from similar stratigraphic levels in Member I of the Kibish Formation, despite the view that Omo I is more modern in appearance than Omo II. 40Ar/39Ar ages on feldspar crystals from pumice clasts within a tuff in Member I below the hominid levels place an older limit of 198 +/-  14 kyr (weighted mean age 196 +/-  2 kyr) on the hominids. A younger age limit of 104 +/-  7 kyr is provided by feldspars from pumice clasts in a Member III tuff. Geological evidence indicates rapid deposition of each member of the Kibish Formation. Isotopic ages on the Kibish Formation correspond to ages of Mediterranean sapropels, which reflect increased flow of the Nile River, and necessarily increased flow of the Omo River. Thus the 40Ar/39Ar age measurements, together with the sapropel correlations, indicate that the hominid fossils have an age close to the older limit. Our preferred estimate of the age of the Kibish hominids is 195 +/-  5 kyr, making them the earliest well-dated anatomically modern humans yet described.

Additional news story, with photo and map of the Omo Kibish site, is freely available (temporarily) on the Nature.com/news page:
CLICK HERE

Dar

[trehinp]

Thanks Martin and Dar,

This is quite a fundamental confirmation of the oldness of our specie... We can now assert with a reasonable probability that AMM is at least about 200K years old...

I am no specialist of human palaeontology, as you know, my primary interest is in Palaeolithic art and cognitive capabilities, so excuse me if my questions are naive...

How similar or different are those very old skulls from today's human beings skulls ? (underlying question : what can we infer of their cognitive abilities?)

Are there enough subsequent more recent skulls to start to trace the migration of AMM in Africa until they got out of that continent ?

Yours sincerely.

Paul

[Daryl Habel]

This is quite a fundamental confirmation of the oldness of our specie... We can now assert with a reasonable probability that AMM is at least about 200K years old...

Hi Paul,

Well, it's a pretty good piece of evidence that a trend toward anatomical modernization is reasonably early (at least 200K yrs ago in East Africa).  But there's always the thorny issue of defining anatomically modern man (your AMM, or what physical anthropologists (PA's) usually refer to as AMH, anatomically modern humans).  There are two skulls from the Omo Kibish deposits newly dated to ~195 ka, roughly the same age with enough differences between them that some PA's would say they are two species, or at least two sub-species.  Omo I looks pretty modern, but Omo II still shows a number of archaic features.  Both have about the same cranial capacity, ~1430 ml.  Just a year or two ago, a skull was discovered at Herto (Ethiopia), modern enough to be widely hailed as the AMH ancestor at ~155K , but not modern enough the authors felt comfortable assigning it to Homo sapiens sapiens (H.s.s.), so they named it Homo sapiens idaltu.  But, despite the possibility that remnant populations existed with variable traces of archaic morphology, yes, unless someone discredits the new dating, it does seem reasonably certain that near anatomically modern humans existed ~200K yrs ago in East Africa.  

I am no specialist of human palaeontology, as you know, my primary interest is in Palaeolithic art and cognitive capabilities, so excuse me if my questions are naive...

How similar or different are those very old skulls from today's human beings skulls ? (underlying question : what can we infer of their cognitive abilities?)

Omo I (more modern) and Omo II (more archaic) both have the same cranial capacity, but there are noticable differences in the shape of the braincase.  This sort of thing makes the position of lobes variable, but we don't know how these brains were wired because only the external features of the brain fossilize as endocasts.  We also know that in modern humans, cranial capacity is variable between ~1000-1900 ml (averaging about 1350 ml IIRC), and we know that in modern humans, some of the most intelligent people who ever lived had very small cranial capacities (much lower than average), it's obvious we can't infer much from the 1430 ml cranial capacity of Omo I and II, nor any other fossil skull with a cranial capacity overlapping AMH (or your AMM).   As a consequence, cognitive abilities for [any] prehistoric human can be inferred only from study of their archaeological context.

It's pretty safe to say that most African populations at 200K were archaeologically in transition to the Middle Stone Age, and this transition had begun in East Africa maybe 200K yrs or more earlier.

Are there enough subsequent more recent skulls to start to trace the migration of AMM in Africa until they got out of that continent ?

This question takes us back to the issue of the definition of anatomically modern.  All I can answer with is that the oldest evidence of the modernization trend outside Africa is the Skhul and Qafzeh populations from modern-day Israel, which are ~130-80 K yrs old.  The oldest in East Asia might be Liujiang (south China), which might be ~100-70 K yrs old.  The oldest European diagnostic  AMH (Oase, Rumania) is currently dated ~36 K yrs old.  There's insufficient fossil material in Eurasia to identify world-encompassing migrations!!  Although there are many African examples for this timespan (post-200 K to the present), the major difficulty is that in many parts of the world (excepting Europe, where 100% of human fossils are diagnostic Neanderthals), the relevant timespan (say, 150-50 ka)  has yielded only scraps of fossil humans which complicates recognition of diagnostic AMH or archaic traits (if the experts ever agree on the definition of AMH).  At present, in my opinion, no one has made a convincing case for an "out-of-Africa" material culture migration (of Later Stone Age, Upper Paleolithic people, although Richard Klein is trying his best)).  But I'd have to assume the first wave out-of Africa by recognizably 'behaviorally' modern humans was eastward across South Asia, probably earlier than 70-60 K, in order to colonize Sahul by about 60-50 K.  There's still a lot to learn before we'll have more than hints.

All this is my humble non-professional dreaded armchair best opinion, but maybe someone with a better understanding will have a better answer.

Cheers,
Dar

[Robert Henvell]

 The age estimate of the two crania are the authors preferred option.Omo 1 was excavated and Omo 11 was found on the surface.The age of both discoveries is tenuous and there is no definative evidence that they are the same age.One or both skulls could be significantly younger.There is a 90Ka gap  and a number of erosional surfaces between the two age estimates.This is not the final answer.

[lagarvelho]

Robert:

I had no idea one of the Omo fossils was found at the surface and the other was buried deeper.  There's been a lot of argument about the "modernity" of these fossils for a long time.  As to their dating, it may mean the fossils are that old, but that they belonged to one rather variable population.  Or they may not have been part of the same population, but separated by hundreds, or thousands, of years.  Which would possibly explain the seeming "primitiveness" of Omo II and the seeming "modernity" of Omo I.  As you say, lots of questions remain.
Anne G

[Daryl Habel]

 The age estimate of the two crania are the authors preferred option.Omo 1 was excavated and Omo 11 was found on the surface.The age of both discoveries is tenuous and there is no definative evidence that they are the same age.One or both skulls could be significantly younger.There is a 90Ka gap  and a number of erosional surfaces between the two age estimates.This is not the final answer.

Well, appreciating your knowledge as a sedimentologist, I'd still have to say that this comment oversimplifies the question of the ages of Omo I and II (using Roman numerals, making the fossils Omo 1 and Omo 2, not Omo 11 as you seem inclined to ascribe it).  Disregarding, for the present, that the more-archaic-looking Omo II was collected from the surface, and therefore has dating that could by your argument  be considered tenuous, that still does not address the dating of the more-modern-looking Omo I.

While it is true that the two 40Ar/39Ar measurements (104/-1 kyr on the Member III tuff, and 196/-2 kyr on the Member I tuff; see Fig. 2) have a 92 ka 'gap' separated by a number of erosional surfaces, the more-modern-looking Omo I was recovered "from a siltstone 2.4 m below the base of Member II" (referenced to Butzer 1969).  While I'm sure it is possible that "this is not the final answer", this new paper does, at least, point toward an age for Omo I that is at least in the range of OIS 6.

In any case, concerning the issue of the trend of anatomical modernity, there are other fossils from Africa dating from post-200 kyr BP (and some that are earlier) which also show derived modern features.  These African fossils do represent the earliest appearance of the trend toward anatomically modern humans and, extrapolating from all presently-known evidence, I'll stand by my original reply to Paul that "near anatomically modern humans existed ~200 K yrs ago in East Africa."  Note also that I prefaced this with "unless someone discredits the new dating" (and this, especially for the more-modern-looking Omo I).  I don't think your oversimplified explanation discredits the Omo I dating by these authors, although dating of Omo II may be more contentious.

Dar

[Robert Henvell]

The rapid rate of sedimentation infers flooding.The crania were probably moved to the locations,where they were discovered,from  original positions upstream.Analysis of the stratigraphic relationships at the locales,where they were discovered is not going to provide definative age estimates.

[Daryl Habel]

The rapid rate of sedimentation infers flooding.The crania were probably moved to the locations,where they were discovered,from  original positions upstream.Analysis of the stratigraphic relationships at the locales,where they were discovered is not going to provide definative age estimates.

Yes, flooding, and probably not one event.  In fact, according to the authors' preferred scenario, sedimentation events for the members I through IV at Omo seem to have a relationship with Mediterranean sapropels associated with "greatly increased flow of the Nile River into the Mediterranean Sea" (p. 735).  Each member at Omo is separated by an unconformity, so there seems no compelling reason to believe that, although rapid sedimentation is inferred, that sedimentation was continuous.  In fact, on page 734, it reads "Member II was incised by as much as 25 m before the deposition of Member III".

It would really have been optimal had they been able to date the "Tuff II' which separates Members I and II (see Fig. 2)., and you are correct that they have only bracketed the age to between 196 +/- 2 and 104 +/- 1 kyr, but you neglect mention that there are three unconformities (and the undated "Tuff II") lying between these dated events, and that at the Omo I (the more-modern-looking fossil) discovery site, which seems particularly well-documented, "the hominid fossils were recovered from a siltstone 2.4 m below the base of Member II".  On Fig. 2, the base of Member II is the position of the undated "Tuff II", above which is 30 meters of stratigraphic representation of four distinct sedimentation types and two unconformities before reaching the Member III dated tuff (104 ka).

Although, I agree that specific details of this report can be questioned, I know Frank Brown has been looking at this particular Turkana Basin stratigraphy for more than 30 years, so I'm favorably inclined toward accepting his opinion of the identification and circumstances of the discovery sites. I'm also inclined toward believing that Omo I age is a lot closer to 196 ka than it is to 104 ka, even though, as you say, the age of ~195 ka is the authors' "preferred option" and "tenuous".

In any case, rarely is "the final answer" contained in the last word spoken.  You raise good questions.  However, until someone discredits this report with a published criticism, the Omo I skull discovery site, in any case, does now seem to be much better documented than previously, and this report does seem to confirm great antiquity (at least OIS 6, I would say) for the Omo I skull.

Dar

       

[trehinp]

Thanks Dar for all those informative explanations.

This is very helpful. Sorry for this late answer, but for some reasons I tried to send a post twice yesterday and the day before and I must have made an error since they didn't appear on the discussion.

I am more and more convinced that there is a continuity in AMH between the early ones and us and less and less believe the theory of authors like Klein, Tatterssall, Mithen who hypothesise a second major change in human specie circa 50K years ago.  If I remember well, they base their claim primarily upon the cultural "explosion" in the upper Palaeolithic, in particular the representative cave art starting around 35Kyears ago. As you know I have another hypothesis to explain that see my  post on the "Parietal & Mobiliary Art" board : "Radical or progressive evolution" (http://www.palanth.com/forum/index.php?topic=423.0)

Again, not being a specialist of Human Palaeontology, I lack the expertise about other anatomical evidence that would tend to prove or disprove continuity between early AMH (OMO I and OMO II) and us.

On my other question which was to understand what was the migration route of AMH out of Africa, thank you also for your excellent answers.

This question takes us back to the issue of the definition of anatomically modern.  All I can answer with is that the oldest evidence of the modernization trend outside Africa is the Skhul and Qafzeh populations from modern-day Israel, which are ~130-80 K yrs old.  The oldest in East Asia might be Liujiang (south China), which might be ~100-70 K yrs old.  The oldest European diagnostic  AMH (Oase, Rumania) is currently dated ~36 K yrs old.  There's insufficient fossil material in Eurasia to identify world-encompassing migrations!!  Although there are many African examples for this timespan (post-200 K to the present), the major difficulty is that in many parts of the world (excepting Europe, where 100% of human fossils are diagnostic Neanderthals), the relevant timespan (say, 150-50 ka)  has yielded only scraps of fossil humans which complicates recognition of diagnostic AMH or archaic traits (if the experts ever agree on the definition of AMH).  At present, in my opinion, no one has made a convincing case for an "out-of-Africa" material culture migration (of Later Stone Age, Upper Paleolithic people, although Richard Klein is trying his best)).  But I'd have to assume the first wave out-of Africa by recognizably 'behaviourally' modern humans was eastward across South Asia, probably earlier than 70-60 K, in order to colonize Sahul by about 60-50 K.  There's still a lot to learn before we'll have more than hints.

However, I was also interested in the migration route while AMH were still on the African continent. A subsidiary question would be to know if we have any idea / estimates about the populations sizes.

This is linked to my hypothesis on the role of people with "Savant syndrome" may have played in the apparition of art. The assumption being that if early AMH were similar to us, then there must have had brain functioning similar to ours, with disabilities as well as exceptional capabilities.

If we were to find a very early art manifestation along the migration route of AMH, this would support my "Savant syndrome" hypothesis. I think that finding such art is a possibility, even though the probability that it existed would be very small, given the very low prevalence of "savant syndrome" in the population and further more the risk that such art manifestation would also be destroyed by time.

Sorry for that slight deviation from the immediate subject of this discussion, I am trying to link this OMO I and OMO II story to my own research.

Yours sincerely.

Paul