Wednesday, 14 December 2016

Ancient Footprints - The Long And The Short Of It

Test-pit L8 at Laetoli Site S.
In the northern part of the test-pit (at the top), the Footprint Tuff is particularly altered, damaged by plant roots and dislodged along natural fractures.

New footprints from Laetoli (Tanzania) provide evidence for marked body size variation in early hominins | eLife

If you want to know why science works and creationism doesn't you could do worse than read and understand this paper.

Creationists often claim to be baffled by the way science derives information from historical records without actually being there to witness it. Curiously, they only seem to be baffled by this when it comes to things they don't want to be true. Ken Ham even proudly teaches children to kill any discussion about the distant past by asking 'Where you there?' knowing the the speaker or teacher wasn't and believing this invalidates everything they've said. It's a neat trick to prevent children learning something you don't want them to know and something that will stand any creationist in good stead well into adulthood.

The same creationists also claim to be baffled by the lack of absolute certainty in science and the way it keeps revising and improving on what it knows and how it adopts tentative answers pending further information and is prepared to ditch or adopt that temporary view later on. To these creationists, of course, certainty is far more important than accuracy and fitting the facts into a predetermined and unchangeable narrative is paramount. The actual truth is merely incidental to this objective.

So, papers like this on the new set of fossilised footprints found in Laetoli, Tanzania, close to the famous set found in 1970, will be dismissed. Not only was no-one alive to day there to witness them being made because they were made 3.66 million years ago, but some of the conclusions drawn from them are tentative and may or may not add to our understanding of these hominins who might well be ancestral to our own species. The new tracks were both going in the same direction as the 1970 tracks.

Shaded 3D photogrammetric elevation model of a cast of the southern portion of the Site G trackway with close-ups of selected hominin tracks with contour lines.
Colour renders heights as in the colour bar; distance between elevation contour lines is 2 mm. The empty circles and squares indicate the position of the targets.

Laetoli is a well-known palaeontological locality in northern Tanzania whose outstanding record includes the earliest hominin footprints in the world (3.66 million years old), discovered in 1978 at Site G and attributed to Australopithecus afarensis. Here, we report hominin tracks unearthed in the new Site S at Laetoli and referred to two bipedal individuals (S1 and S2) moving on the same palaeosurface and in the same direction as the three hominins documented at Site G. The stature estimates for S1 greatly exceed those previously reconstructed for Au. afarensis from both skeletal material and footprint data. In combination with a comparative reappraisal of the Site G footprints, the evidence collected here embodies very important additions to the Pliocene record of hominin behaviour and morphology. Our results are consistent with considerable body size variation and, probably, degree of sexual dimorphism within a single species of bipedal hominins as early as 3.66 million years ago.

eLife digest
Fossil footprints are extremely useful tools in the palaeontological record. Their physical features can help to identify their makers, but can also be used to infer biological information. How did the track-maker move? How large was it? How fast was it going?

Footprints of hominins (namely the group to which humans and our ancestors belong) are pretty rare. Nearly all of the hominin footprints discovered so far are attributed to species of the genus Homo, to which modern humans belong. The only exceptions are the footprints that were discovered in the 1970s at Laetoli (in Tanzania) on a cemented ash layer produced by a volcanic eruption. These are thought to have been made by three members of the hominin species Australopithecus afarensis – the same species as the famous “Lucy” from Ethiopia – around 3.66 million years ago.

The extent to which body shape and size varied between different members of Au. afarensis – for example, between males and females – has been the subject of a long debate among researchers. Based on the skeletal remains found so far in East Africa, some scholars believe that individuals only varied moderately, as in modern humans, while others state that it was pronounced, as in some modern apes like gorillas.

Masao et al. have now unearthed new bipedal footprints from two individuals who were moving on the same surface and in the same direction as the three individuals who made the footprints documented in the 1970s. The estimated height of one of the new individuals (about 1.65 metres) greatly exceeds those previously published for Au. afarensis. This evidence supports the theory that body size varied considerably amongst individuals within the species.

Masao et al. tentatively suggest that the new footprints can be considered as a whole with the 1970s ones. The tall individual may have been the dominant male of a larger group, the others smaller females and juveniles. Thus, considerable differences may have existed between males and females in these remote human ancestors, similar to modern gorillas.

The newly discovered tracks are only 150 metres away from the previously discovered sets of footprints. This leaves open the possibility that additional tracks may be unearthed nearby that will further our knowledge about the variability and behaviour of our extinct ancestors.

The full set of tracks, including the 1970 set were almost certainly made at the same time in the same layer of fresh, fine volcanic ash which had been moistened by rain and turned into a clay-like substance. The tracks were subsequently buried, preserving the footprints and the record of the passing of this group of beings with feet that are almost identical to those of modern humans.

But this species was not human and not even hominid; it was almost certainly the same species as the famous 'Lucy', Australopithecus afarensis, from what is today the Afar region of Ethiopia. This is assumed because Au. afarensis was known to live nearby at that time.

So what can be deduced from these footprints? Apart from the fact that this species had a 'human' foot and was bipedal, so showing that bipedalism and the modern human foot had evolved before there were even humans, there is the fact that one of the group was considerably larger and heavier judging by the stride and depth of the cast. The assumption is that this was probably a male with a group of females juveniles and children. He is certainly the largest Australopithecine so far discovered.

If this is so it tells us that there was considerable sexual dimorphism in Au. afarensis, unlike in Homo sapiens where sexual dimorphism in terms of height and weight is not nearly so pronounced. This might help settle a current disagreement amongst palaeoanthropologists over whether there was any dimorphism and, if so how much. But this is speculative, so what science does is flag this up as a distinct possibility, not yet an established fact but certainly not lending weight to the opposite conclusion.

Also if this is true it means the rather romantic idea of the 1970 footprints being those of a mother, father and child is probably wrong. It could be two women and a child or a female, adolescent male and a child. In other words the original conclusion about age and gender of the individuals could be wrong.

Why creationists find this puzzling is itself a puzzle. It doesn't illustrate the unreliability of science but rather the opposite. What would be unreliable would be to declare an idea proven then not bother to look for more evidence or, like creationists do, decide what the conclusion must be then accept or reject the evidence depending on whether it agrees with the conclusion.

What the team want to do now is to excavate the area between this recent find and the original find because it might well be that there are more tracks still to be discovered and that this was a larger band travelling together with more than the five we now know about.

Perhaps one of my creationist readers (only joking!) would tell me why I needed to be there to accept this evidence for what it is and form some tentative conclusions based on this evidence. Perhaps they could tell me also why forming definite conclusions ahead of the facts and dismissing evidence on spurious grounds if it doesn't fit that conclusion is a more honest and reliable then continuing to look for better evidence and being to change you mind if the facts change.

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  1. I've had this "were you there" question a couple of times and my response has always been to say '"yes I was'". The questioner usually comes out with a denial that this could be the case which then demands the return question: "how do you know I wasn't, were you there?"


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