Wednesday, March 17, 2010

digging more dirt on our ancestors

the unique Sima de los Huesos, or Pit of Bones

Widening the picture considerably, my mini-research has uncovered a site in the Sierra de Atapuerca in Spain, with evidence of human, or at least Homo, tool-making, dating back some 800,000 years. Compare this to the 'little lady of Flores', which seems to represent another Homo species from a mere 18 kya, and you begin to realize how complicated and ever-changing [at least in terms of our knowledge] the human, or Homo, story has become.
I've found here a list of important sites for hominid remains, and I'll look at each site in turn and report from them, and we'll see what conclusions we can draw and what questions we can raise.

The Atapuerca caves are in an ancient karst topography in Spain, and in one of those caves the remains of a hominid, either Homo erectus or perhaps Homo antecessor, has been found. They've been dated at around 886 kya, according to one authority, though others put them at about 780 kya 'based on paleomagnetic measurements'. In any case, the claim is that these are the oldest hominid remains ever found in Europe, though this, unsurprisingly, is contested. The Gran Dolina trench [dug out for a railway line in the 1890s], where this specimen was found, has eleven levels of human, or Homo, occupation. The oldest remains have been difficult to identify in terms of species, and the Homo antecessor designation isn't certain.

The current thinking on Homo antecessor is that they were probably cannibalistic, that they flourished between 1.2 million years ago and 800 kya [the lower Pleistocene], and that they were the direct predecessors of Homo heidelbergensis [if not the same species]. H heidelbergensis flourished in the Pleistocene, 600 to 250 kya. They're also almost identical to the African species, Homo ergaster. The finding of these specimens, in Gran Dolina and elsewhere, have, in the last couple of decades, transformed our thinking about hominids in Europe, pushing them back almost half a million years.

The Pleistocene actually extends from 1.8 million years ago to about 10 kya, after which it's the Holocene. So now I know.

Level 6 of the Dolina trench has proved most productive of hominid and other fossil remains. This is where the 800 kya fossils were found. Level 11, by the way, is the topmost layer, and level one at the bottom, which is counter-intuitive to me. Some stone tools and animal remains have been found as low as level 4, dating back a million years, but no hominid remains as yet. There have also been other sites nearby [Galeria and Elefante] that have yielded important finds.

The cave of Sima de los Huesos, in this region, has yielded the most fascinating material – a huge number of hominid bones dating to 400 kya, and tentatively identified as H heidelbergensis. Dating of these cave remains has proved very tricky, and I might just post on the various dating techniques and their limitations later on in this autodidactic odyssey.

The excavation work at Sima de los Huesos is ongoing, and has already yielded remains of thirty individuals. It's an unprecedented collection of closely related hominids. There's also the mystery of how they all came to be there at the one time – there are no signs that they actually lived there. Did they shelter there, were they imprisoned there, or was the place used as a convenient burial, or body disposal, site? The earliest certain evidence of planned burial is associated with H neanderthalensis, less than 100 kya.

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