Fossils are a window to the past: but rarely are such windows clear. And looking at a thing through "a glass distorted", of course, distorts our view of that thing. Restoring the appearances of prehistory's creatures is difficult; reconstructing their behavior is often impossible. But once in a long while paleontologists find—preserved perfectly by petrifaction—easily legible evidence of a long-dead organism's daily habits.
Such was the case earlier this year with Archaboilus musicus, a 165-million-year-old katydid/bush-cricket (Tettigoniidae) found in that fount of glorious fossils, China. Its modern kin, naturally, are well-known for their males' stridulatory songs, used to attract mates: and it turns out at least some of them did the same as early as the Jurassic Period. By examining the hind angles of the forewings belonging to A. musicus' (presumably male) holotype, and comparing these stridulatory organs to those of extant katydids, researchers have deduced the precise sound of the ancient katydid's song—which was indeed musical, like the melodies of its modern kin (http://www.youtube.com/watch?v=gC6vVmkU8i0).
Interestingly, with a frequency of 6.5 kHz, A. musicus had a rather lower bandwidth than most of its said extant cousins. It's speculated that this reflects the different constituency of Jurassic forests: dominated not by tall, shady deciduous trees, but by thick fern bracken underneath conifers—deep acoustics would be required to penetrate this more claustrophobic sylvan environ.
Merry Christmas to all, and to all a good night...
Gu, J. J.; Montealegre, Z.; Robert, D.; Engel, M. S.; Qiao, G. X.; and Ren, D. (2012). Wing stridulation in a Jurassic katydid (Insecta, Orthoptera) produced low-pitched musical calls to attract females. Proceeding of the National Academy of Sciences of the United States of America, 109 (10): 3868.