New Laetoli Footprints Demonstrate Full Bipedality

A story running in Newsweek and the Washington Post (and other outlets, presumably), details research into the newly discovered fossil footprints at Laetoli dated to 3.6 mya that clearly show a modern human gait.

Two sites in Laetoli, Tanzania, feature footprints of human ancestors who lived about 3.6 million years ago. They were members of the genus Australopithecus. That's the genus of “Lucy,” the 3.2 million-year-old human ancestor whose fossilized bones were discovered in Ethiopia in 1974.

David Raichlen, an evolutionary anthropologist at the University of Arizona, has studied the Laetoli footprints and compared them to footprints made by human volunteers in laboratory settings. He examined footprints of individuals walking normally and also those walking with bent knees and bent hips. (Scientists who study locomotion use the acronym BKBH). The Laetoli footprints more closely match modern human footprints.

“Upright, humanlike bipedal walking goes back 4 to 5 million years,” Raichlen told The Washington Post in advance of a symposium on the evolution of human locomotion, which took place Sunday at the Experimental Biology 2018 conference in San Diego.

This dovetails with the recent findings that Ardipithecus, a hominin dated to around 4.4 mya, likely could travel equally well on the ground or in the trees.  Oddly, the WaPo article doesn't mention this.  

3.3 Million Year Old Vertebral Column Confirms Human Pattern of Au. afarensis

The science site PhysOrg has posted a story on a study of the 3.3 million year old fossil from the site of Dikika, in the Afar Triangle.  The fossil, known as Selam, is an almost complete skeleton of a 2 ½ year-old child. From the story:

Many features of the human spinal column and rib cage are shared among primates. But the human spine also reflects our distinctive mode of walking upright on two feet. For instance, humans have fewer rib-bearing vertebrae - bones of the back - than those of our closest primate relatives. Humans also have more vertebrae in the lower back, which allows us to walk effectively. When and how this pattern evolved has been unknown until now because complete sets of vertebrae are rarely preserved in the fossil record.

"For many years we have known of fragmentary remains of early fossil species that suggest that the shift from rib-bearing, or thoracic, vertebrae to lumbar, or lower back, vertebrae was positioned higher in the spinal column than in living humans. But we have not been able to determine how many vertebrae our early ancestors had," said Carol Ward, a Curator's Distinguished Professor of Pathology and Anatomical Sciences in the University of Missouri School of Medicine, and lead author on the study. "Selam has provided us the first glimpse into how our early ancestors' spines were organized."

This gives us much better evidence of how bipedality was practiced in some of the earliest hominins. We know, from the footprints at Laetoli and the hip remains of Lucy, that Au. afarensis was bipedal but now we know that the rib structure had evolved into a more human pattern. 

Laetoli Footprints To Be Visible Again

AllAfrica.com is reporting that the Laetoli footprint tracks, produced by two side-by-side hominids some 3.6 million years ago, will be visible again and open for tourists. The author writes:

The state's announcement to open the site may see the beginning of the end for stirring debate over how to best protect the 3.6-millionyear- old tracks. In recent years, experts have been expressing fear for oldest human footprints fossilized tracks preservation, saying weathering has begun to undermine those protections, raising concerns that the prints preserved in a volcanic ash bed could be harmed by erosion, livestock or humans. It has prompted Tanzanian anthropologist Charles Musiba to call for the creation of a new museum to reveal and display the historic prints. But foreign anthropologists question this idea ... as they did when the tracks were covered ... because Laetoli is several hours' drive into Ngorongoro Conservation Area, making guarding and maintaining any facility extremely difficult.

A file photo of the tracks is above. It would be a shame if they cannot be saved. Even though we have casts of them, the original is priceless.

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New 3.6 Million Year Old A. afarensis Remains

Science Daily reports that Yohannes Haile-Selassie's team in Ethiopia have found the remains of a 3.6 million year old Australopithecus afarensis individual that preserves enough of the post-cranium (below the head) to determine that bipedalism had completely taken hold of this species by this time. Of the individual, which is taller than Lucy (AL-288), he says this:

"As a result of this discovery, we can now confidently say that Lucy and her relatives were almost as proficient as we are walking on two legs, and that the elongation of our legs came earlier in our evolution than previously thought," he said in a statement. He explained, "

"All of our understanding of Australopithecus afarenis' locomotion was dependent on 'Lucy.' Because she was an exceptionally small female with absolutely short legs, this gave some researchers the impression that she was not fully adapted to upright walking. This new skeleton falsifies that impression because if 'Lucy's' frame had been as large as this specimen, her legs would also have been proportionally longer."

There is, thus, considerable variability in A. afarensis (this may yet revive the multiple species hypothesis that was put forth in the late 1970s about this material) This finding is expected, however, if the tracks at Laetoli are those of A. afarensis. We have good evidence that those are the tracks of a completely bipedal hominid.

If Ardipithecus ramidus ('Ardi') represents an ancestor to Australopithecus afarensis, then a considerable amount of evolution in bipedality occurred within 800 k years. A check of PNAS reveals that the paper is not out yet, but should be in a few days. Within the context of the debate concerning Ardipithecus' place on the fossil bush and the status of the reconstruction, it is important to remember what Owen Lovejoy wrote concerning Ardipithecus:

Ardipithecus ramidus now reveals that the early hominid evolutionary trajectory differed profoundly from those of our ape relatives from our clade’s very beginning. Ar. ramidus was already well-adapted to bipedality, even though it retained arboreal capabilities. Its postcranial anatomy reveals that locomotion in the chimpanzee/human last common ancestor (hereafter the CLCA) must have retained generalized above-branch quadrupedality, never relying sufficiently on suspension, vertical climbing, or knuckle walking to have elicited any musculoskeletal adaptations to these behaviors.

It is clear that, by 3.6 million years ago, those arboreal tendencies were gone. While it is still being debated whether or not Ardipithecus developed bipedality in the forest or in the forest fringe, the dessication of the landscape continued during the late Pliocene, and the remains of Kadanuumuu strongly suggest that early A. afarensis had completely adapted to this landscape.

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Laetoli Footprints Those of Completely Bipedal Human

Thirty years ago, a set of footprints was discovered in an ash layer at the African site of Laetoli and dated to 3.6 million years ago. This corresponded to the time range of Australopithecus afarensis but it was not sure whether or not this reflected the gait of afarensis, which was, at the time, thought to be somewhat bent-kneed and not truly bipedal in a modern sense. Now, Science Daily news has a story that reconstruction simulation research has determined that those individuals that made the tracks walked bipedally in a modern fashion. The author writes:

Since the Laetoli tracks were discovered, scientists have debated whether they indicate a modern human-like mode of striding bipedalism, or a less-efficient type of crouched bipedalism more characteristic of chimpanzees whose knees and hips are bent when walking on two legs.

To resolve this, [David] Raichlen and his colleagues devised the first biomechanical experiment explicitly designed to address this question.

The team built a sand trackway in Raichlen's motion capture lab at the UA and filmed human subjects walking across the sand.

"Based on previous analyses of the skeletons of Australopithecus afarensis, we expected that the Laetoli footprints would resemble those of someone walking with a bent knee, bent hip gait typical of chimpanzees, and not the striding gait normally used by modern humans," Raichlen said.

"But to our surprise, the Laetoli footprints fall completely within the range of normal human footprints," he added.

This is the next step from the bipedal gait found in Ardipithecus, which may have been reflected in the earliest australopithecine, A. anamensis and, perhaps, early A. afarensis. By this point, Bipedalism was the preferred means of getting around.