This is the skull of an arthrodire, an armored placoderm from the Devonian.
Somehow, 20 foot long predatory fish with a mouth lined with razor-edged bony shears has never made me think of sexy time…until I ran across this comparison image.
Oh, schwiiing. It really doesn't take much to get a mammal to associate just about anything with sex. And then, what do you know, the latest Nature has a short article on an interesting fossil: it's the pelvic region of an arthrodire, Incisoscutum ritchiei, and look what it's got: an ossified clasper, comparable to the erectile organ of modern sharks. This is a bony rod that would have been the core of an intromittent organ in the living animal, so what we have here is a small relic of the sex life of a big fish from a few hundred million years ago.
a, Pelvic girdle in dorsal view; b, pelvic girdle restored.
Think about this, you over-sexed apes: what will be left of your manhood 300 million years from now?
Ahlberg P, Trinajstic K, Johanson Z, Long J (2009) Pelvic claspers confirm chondrichthyan-like internal fertilization in arthrodires. Nature 460:888-889.