The team states that the footprints are from Homo erectus or Homo ergaster (early Homo erectus), ancestors of modern Homo sapiens (modern humans).
Most importantly, these ancestors are considered by scientists to be the first hominids (members of the primate family Hominidae that includes humans, which are the only species still living) to have had the same body proportions as modern humans.
The CNN article “Ancient footprints: Earliest signs of modern feet” quotes the international team to have said, “These rarest of impressions yielded information about soft tissue form and structure not normally accessible in fossilized bones. The Ileret footprints constitute the oldest evidence of an essentially modern human-like foot anatomy.”
The team of international geologists and scientists on this quest of prehistoric humans are from Kenya, South Africa, the United Kingdom, and the United States. They published the findings of their work in the February 27, 2009 issue of Science.
The title of their Science paper is “Early Hominin Foot Morphology Based on 1.5-Million-Year-Old Footprints from Ileret, Kenya.”
They state in the abstract to their Science paper, “Hominin footprints offer evidence about gait and foot shape, but their scarcity, combined with an inadequate hominin fossil record, hampers research on the evolution of the human gait.”
Page two talks about their excavations, with statements from their paper and from the CNN article.