Saturday science subject: Footprints

Reconstructed homo erectus. Source: Wikimedia Commons.

A field school group led by John W.K. Harris of Rutgers University has discovered some rather old footprints in sedimentary layers in northern Kenya. According to ScienceDaily, the footprints were left by early humans some 1.5 million years ago. Harris and his colleagues related their findings in the journal Science:

The authors of the Science paper reported that the upper sediment layer contained three footprint trails: two trails of two prints each, one of seven prints and a number of isolated prints. Five meters deeper, the other sediment surface preserved one trail of two prints and a single isolated smaller print, probably from a juvenile.

In these specimens, the big toe is parallel to the other toes, unlike that of apes where it is separated in a grasping configuration useful in the trees. The footprints show a pronounced human-like arch and short toes, typically associated with an upright bipedal stance. The size, spacing and depth of the impressions were the basis of estimates of weight, stride and gait, all found to be within the range of modern humans.

Based on size of the footprints and their modern anatomical characteristics, the authors attribute the prints to the hominid Homo ergaster, or early Homo erectus as it is more generally known. This was the first hominid to have had the same body proportions (longer legs and shorter arms) as modern Homo sapiens. Various H. ergaster or H. erectus remains have been found in Tanzania, Ethiopia, Kenya and South Africa, with dates consistent with the Ileret footprints.

Reportedly, the size and pattern of the footprints suggest they were left by individuals about 5'9" (1.75 m) tall. ScienceDaily notes that the footprints "constitute the oldest evidence of an essentially modern human-like foot anatomy." Foot bones are generally hard to come by, the site adds, because they're small and the flesh that encases them makes an easy meal for predators.

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