Reverbs of bat echolocation studies

Many bats are famous for their ability to navigate by a biological form of sonar, often called echolocation. So it made news a couple of years ago when scientists concluded that the ancient bat Onychonycteris finneyi apparently could not perform that feat — a hint that bats evolved the ability to echolocate after they took to the sky (SN: 2/16/08, p. 99). Now, new findings may upend that view, once again clouding the earliest stages of bat evolution. O. finneyi was a songbird-sized species of bat that lived between 50 million and 54 million years ago in what is now western Wyoming. Certain features of that bat’s inner ear, and the shape of the stylohyal bone, which stretches between the larynx and the inner ear, suggested that O. finneyi couldn’t echolocate to navigate or find prey. But a new study of modern bats shows that those features don’t definitively rule out echolocation.

That study was published online in Nature back on January 16, but didn’t make into the news then because I was busy at the time covering a meteorological meeting in Atlanta. But because the new work substantially revises the findings I reported in 2008, it seems worth mentioning to keep bat fans abreast of the latest echolocation intelligence.

In the new paper, biologist Brock Fenton of the University of Western Ontario in Canada and his colleagues identify a key clue about a bat’s echolocation powers: whether the stylohyal bone makes contact with the tympanic bone, which houses the bat’s inner ear.

In 21 of 26 bat species that the team analyzed, the stylohyal bone made contact with (or was fused to) the tympanic bone. All of those 21 used high-pitched squeaks from their larynx to echolocate. In four species that don’t echolocate, the stylohyal and tympanic bones don’t make contact, the team found. (The bones also weren’t connected in one other species that echolocates by producing sharp clicking sounds with its tongue.)

In O. finneyi, a close look at fossils shows that the stylohyal bone makes contact with the tympanic bone. So that bat may have been able to echolocate after all, says Fenton. On the other hand, that contact may have resulted from a shift in the bones during fossilization, he admits: “The fossils are pretty much crushed, pancaked.”

Nevertheless, Fenton adds, the possibility that O. finneyi could echolocate can no longer be so easily dismissed. It will probably take yet-to-be-discovered, better preserved fossils to settle the question.