WASHINGTON Footprints found in Kenya that resemble those left in wet sand by beach goers today show that 1.5 million years ago a human ancestor walked like we do with anatomically modern feet, scientists said on Thursday.
The remains of the footprints found in sedimentary rock near Ileret in northern Kenya most likely were left by a human ancestor called Homo erectus, also known as Homo ergaster, an international team of scientists wrote in the journal Science.
The scientists found a series of footprints, including one apparently left by a child, left by individuals walking on a muddy river bank. Judging from stride length, they estimated the individuals were about 5-foot-9 (1.75 meters) in height.
"It was kind of creepy excavating these things to see all of a sudden something that looks so dramatically like something that you yourself could have made 20 minutes earlier in some kind of wet sediment just next to the site," archaeologist David Braun of the University of Cape Town in South Africa, one of the researchers, said in a telephone interview.
"These could quite easily have been made on the beach today," Braun added.
The footprints show that the individuals had a big toe parallel to the other toes, unlike that of other apes where it is separated in a grasping configuration useful in the trees. The footprints show a characteristic human-like arch and short toes, typically associated with an upright bipedal stance.
The size, spacing and depth of the footprint impressions allowed the scientists to estimate weight, stride and gait, which all were found to be within the range of modern humans.
Our species, Homo sapiens, first appeared 200,000 years ago. But this shows that at least as far back as 1.5 million years ago, the human lineage walked with a modern stride, the researchers said.
The findings mark one of the most important discoveries in recent years regarding the evolution of human walking.
Matthew Bennett of Bournemouth University, another of the researchers, said the findings show that these individuals had evolved an essentially modern human foot function and a style of bipedal locomotion matching today's people.
These are the second-oldest known footprints of human ancestors. The oldest, found in Tanzania, date from about 3.75 million years ago and apparently were made by a much more primitive human ancestor called Australopithecus.
These are smaller and show signs of bipedal posture but with a shallower arch and a more ape-like, divergent big toe.
The species Homo erectus had a smaller brain than modern people but had generally similar body proportions -- longer legs and shorter arms -- to Homo sapiens. Their remains have been found in Tanzania, Ethiopia, Kenya and South Africa, with dates consistent with the newly reported footprints.
But no remains of their feet have been found from that time period, Braun said.
(Editing by Philip Barbara)
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