The Laetoli fossil beds of Tanzania in are famous for fossils, especially the early Australopithecus, ‘Lucy’. But one bed has fossilized footprints of dozens of animals, including at least one Australopithecus.
This winter an international team of researchers report a reassessment of one of these traces, prints of something bipedal that is not an Australopithecus [2]. This was initially identified as tracks made by a young bear.
The new research makes the case that this was not a bear. And if not a bear, then it seems to be a second species of hominid. If so, then there were more than one kind of walking erect hominids living there at the same time.
Cool.
And we do mean the same time. All the prints in the deposit were laid down within a few hours, possibly a few minutes of each other. As one of the researchers puts it, something could have “looked up across the landscape and saw an Australopithecus afarensis walking somewhere else,” (Dr. Ellison McNutt, quoted in [1])
The paper makes the case that the unknown footprint is not a bear. While bears do walk upright, they generally don’t walk more than a few steps upright. (Anyone who watches nature shows on TV knows that.) They also found evidence of a cross step, which humans do to keep balance, but bears cannot do. (They would, of course, drop to all fours instead.)
If this is not a bear, then it isn’t clear what it is. Whatever it was, walks upright like a human, though. So this is likely an ancestor of ours. Another ancestor of ours, and presumably some kind of a cousin of Lucy.
This is hardly the first evidence for a complicated, “braided” family tree, with many strains of “human” emerging and living at the same time. Only with the final extinction of the Neanderthals has Homo sapiens become the only kind of people on the planet. Up til then, there had always been multiple strains of “human”.
This is also strong evidence that walking upright was a very early development in human evolution, developing before large brains, tool making, and quite possibly before language. It is far from obvious why erect bipedalism would be an advantageous adaptation, but it certainly seems to have stuck around.
The best part of this study, though, is an empirical test of how baby bears walk. Four rescued bear cubs were invited to walk upright across mud to get some yummy treats. The resulting trackways were used as comparisons to the fossil track.
“We ended up with four little juvenile bears that we had stand up and walk through mud for either applesauce or maple syrup, which was very cute, as their reward at the end of it,”
(Dr. Ellison McNutt, quoted in [1])
(I’ll note that the research report is almost satirical in the required discussion of sampling, indicating that “Blinding was not relevant to the data collected on the non-human comparative species” ([2], p. 5). I.e., they did not make sure that the baby bears did not know the hypothesis being tested, lest their behavior be influenced. : – ) )
- Nell Greenfieldboyce, Ancient footprints mistakenly attributed to bears were made by early humans, in NPR News – Science, December 1, 2021. https://www.npr.org/2021/12/01/1060208486/ancient-footprints-mistakenly-attributed-to-bears-were-made-by-early-humans
- Ellison J. McNutt, Kevin G. Hatala, Catherine Miller, James Adams, Jesse Casana, Andrew S. Deane, Nathaniel J. Dominy, Kallisti Fabian, Luke D. Fannin, Stephen Gaughan, Simone V. Gill, Josephat Gurtu, Ellie Gustafson, Austin C. Hill, Camille Johnson, Said Kallindo, Benjamin Kilham, Phoebe Kilham, Elizabeth Kim, Cynthia Liutkus-Pierce, Blaine Maley, Anjali Prabhat, John Reader, Shirley Rubin, Nathan E. Thompson, Rebeca Thornburg, Erin Marie Williams-Hatala, Brian Zimmer, Charles M. Musiba, and Jeremy M. DeSilva, Footprint evidence of early hominin locomotor diversity at Laetoli, Tanzania. Nature, 2021/12/01 2021. https://doi.org/10.1038/s41586-021-04187-7
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