By painstakingly measuring hundreds of specimens of a fossil mammal called Thyrohyrax, recovered from the famous fossil beds of Egypt's Fayum Province, the researchers determined that males of this now-extinct species -- and only males -- had oversized, swollen lower jaws shaped much like a banana. Further, the team speculated, the animals may have used the balloonlike structural chamber that shaped their bizarre jaws to produce sound.
If this speculation is correct, Thryohyrax and its fossil relatives would be the only mammals found so far to use such a skeletal structure for producing sound, the researchers said. They added that some dinosaurs are thought to have used similar sound-producing mechanisms.
The researchers published their findings in the March issue of the Journal of Vertebrate Paleontology, which was released in mid-April. The study's lead author is Donald DeBlieux, a former research associate at the Duke Lemur Center (formerly the Primate Center) who is now at the Utah Geological Survey. Other team members from Duke include Elwyn Simons, head of the Division of Fossils at the Duke Lemur Center; Prithijit Chatrath, curator of the division; and Michael Baumrind, a former undergraduate anthropology student who initiated the research as a senior project. Yousry Attia of the Egyptian Geological Survey also participated in the study.
The team's research was supported by the National Science Foundation.
The banana-jawed hyraxes were much different in appearance from their modern counterparts, the scientists said.
"Hyraxes today are improbably cute-looking mammals that are about the size of rabbits, look much like guinea pigs and have a penchant for sunbathing," Simons said. "Seven species of hyraxes now inhabit a swathe from the Middle East to southern Africa