Fossils, which included tiny middle ear bones called the ossicles, dating back as early as two million years ago, are shedding light on the auditory abilities of our human ancestors.

In a new study published in the journal Science Advances on Sept. 25, researchers analyzed the bones of the Australopithecus africanus and Paranthropus robustus.

Using computerized tomography scans, the researchers virtually reconstructed the ears of these early hominins from South Africa revealing that these two species were very sensitive to close-range sounds, hearing them more intensely compared with both humans and chimpanzees do now.

Study researcher Rolf Quam, from Binghamton University's Department of Anthropology , said that these species were capable of hearing softer sounds compared with humans and chimps and that their heightened sensitivity to sound ranging from 1.5 to 3.5 kilohertz allowed them to make vocalizations to one another from up to 75 feet away in the open savanna.

"Compared with chimpanzees, both early hominin taxa show a heightened sensitivity to frequencies between 1.5 and 3.5 kHz and an occupied band of maximum sensitivity that is shifted toward slightly higher frequencies," Quam and his colleagues wrote in their study.

The species could have used the so-called "voiceless consonants" because the vocal chords do not move when these are produced.

The sounds, which are now used in modern-day communication and include the sounds produced by the letters 'K,' 'T,' 'Th,' 'F' and 'S,' have likely helped facilitate short-range vocal communication in an open habitat at the time.

"[The hominins'] hearing pattern is similar to a chimpanzee['s], but slightly different," Quam said. "That difference seems to be in the direction of humans."

Earlier research on the tooth enamel of prehistoric humans suggests that they consume foods that are found in both forests and savanna so these hominins may have thrived in both of these environments.

"It turns out that this auditory pattern may have been particularly favorable for living on the savanna. In more open environments, sound waves don't travel as far as in the rainforest canopy, so short-range communication is favored on the savanna," Quam said.

The human line separated from chimps about 5 to 7 million years ago and the hearing ability of human ancestors started to adapt to lifestyle changes.

The researchers said that they are on the track to reconstructing how hearing has changed from chimp-like pattern to a human-hearing pattern.

Photo: Ryan Somma | Flickr

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