Just because I work on archosaurs does not make me immune to the charms of other fossils (well, not quite all of them anyway). Who, after all, could be anything but charmed and intrigued by the lower jaw of Helicoprion? This ancient shark has perhaps the oddest dental arrangement of any vertebrate and probably had the most expensive dental bills.
While we are on aquatic non-tetrapodan vertebrates do also check out the news on the new giant filter-feeding fish that’s just out. Featuring research by the wonderful Jeff Liston and art from Musings buddy Bob Nicholls.
Dave Hone's Archosaur Musings 
I was really confused until I saw the illustration at the bottom right of the photo.
And now I’m even more confused. That’s amazing 🙂 *Any* idea why the jaw was like that?
Yes, tis a bit odd to say the least. I don’t know what the consensus is having not read any research on the subject, but my guess is that it is an extreme and unsusual form of the normal ‘conveyor belt’ system of tooth replacement in sharks. The ‘cookie cutter’ shark has something vaguely analguous as I recall, though Wikipedia probably knows better than me…
I was just reading about the fantastic Carboniferous chondricthyes known as the Agassizodontids the other day and here you are with a musing about their most extravagant and exotic exemplar. The ancient seas of Idaho sure did teem with an unlikely and seemingly maladaptive bunch.
Some killjoys at the Smithsonian reconstructed it with the tooth-whorl deep in the throat, like a basking shark on amphetamines. However, despite their arguments about the hydrodynamic inefficiency of a symphyseal whorl, I won’t put much of anything past sexual selection now that David Attenborough has shown me the lyrebird.