According to Simons, today's hyraxes are relics of a time when Africa lacked most of the kinds of animals found there today. Current scientific thought holds that most modern mammal groups diversified and became larger only after a giant asteroid killed off the dinosaurs 65 million years ago.
Numerous ecological niches vacated by the annihilated dinosaurs were waiting to be filled. One group of creatures, called the Afrotheres -- "Beasts from Africa" -- seized the opportunity. It was from this group, Simons said, that today's hyraxes descended.
The Afrotheres, whose descendents include elephants and aardvarks as well as hyraxes, diversified into various niches and ultimately became Africa's dominant land animals.
As hyraxes diversified, the development in Thyrohyrax of a curved, swollen jaw containing a hollow chamber represented a particularly strange adaptation, DeBlieux said. Some other hyracoid species also showed a similar adaptation, but the skeletal trait was most pronounced in Thyrohyrax, he added.
"Our team had long speculated on the cavity's purpose, " Simons said. "One idea we proposed, for example, was that the chamber contained enlarged salivary glands.
"Our current findings narrow down the possibilities," he said. "Among the most plausible explanations is that the hollow jaw was a sound-producing device." The animals, he added, may have used the chamber to produce sounds as part of their courtship or mating displays.
According to DeBlieux, help in refining explanations behind this mammal's unusual jaw may come from studying dinosaur models. In particular, he said, a number of museums have built models of dinosaur sound-producing skeletal cavities that have enabled scientists to reconstruct the possible sounds made by them.
Now, DeBlieux would like to do the same for the fossil hyrax. "It would be really neat," he said, "to model their jaws so we cou