An individual from an unknown hominid (原始人类) species walked across a field of wet, volcanic ash in what is now East Africa around 3.66 million years ago, leaving behind a handful of footprints.

Those five ancient footprints, largely ignored since they were partly unearthed at Tanzania’s Laetoli site in 1976, show features of upright walking by a hominid, a new study finds. Researchers had previously considered them hard to classify, possibly produced by a young bear that took a few steps while standing. But the latest analysis refutes that suggestion.

McNutt, DeSilva, who started the new investigation as a Dartmouth College graduate student, and their colleagues fully dug out and cleaned the five Laetoli footprints in June 2019. Then they measured, photographed and 3-D scanned the ancient tracks. McNutt’s group focused on two footprints that were particularly well-preserved. Foot shapes, sizes, and walking characteristics of the Laetoli individual differed in various ways from those of other hominid individuals at the same site. The prints also didn’t match those from modern black bears and modern chimps (黑猩猩) walking upright.

The Laetoli individual possessed a wider, more chimplike foot than humans, the researchers say. Its big toe stuck out slightly from the second toe (脚趾), but not to the degree observed in chimps. On one step, the Laetoli individual’s left leg crossed in front of the right leg, leaving a left footprint directly in front of the previous track. People may cross-step in this way when trying to regain balance. And bears and chimps assume a relatively wide standing due to knee and other bone arrangements that prevent them from walking like the Laetoli individual and probably from cross-stepping, the scientists say.

Given that only two of the ancient footprints are complete enough to analyze thoroughly, the possibility that a chimp other than a hominid made the Laetoli footprints can’t be ruled out, says William Harcourt-Smith, a scientist at Lehman College. But evidence of cross-stepping is enough to prove that it was a hominid track maker, he says.

【小题1】What does the underlined word “refutes” in Paragraph 2 mean?

A．Objects to.

B．Supports.

C．Puts forward.

D．Criticizes.

【小题2】Why do researchers think the footprints were unlike those of bears or chimps?

A．They are less chimplike.	B．They have toes sticking out.
C．They show a wider standing.	D．They get features of cross-stepping.

【小题3】What does William think of the new research finding?

A．Challenging.	B．Convincing.
C．Confusing.	D．Conflicting.

【小题4】What is the purpose of the text?

A．To share a new discovery.	B．To describe a major event.
C．To settle a huge disagreement.	D．To introduce an unknown species.