"Part of the problem is that the Hox expression data is available only for a few model organisms," Sallan said. "What's really needed is some expression data from other ray-finned fishes and tetrapods, things that are not mouse and chick and zebrafish. We need to try to get the full diversity of Hox expression."
It's also unclear how Tarrasius used its unexpectedly intricate spinal column in its daily life. Sallan speculates that the bony vertebrae may have been useful in propelling the fish's body during fast swimming, similar to the stiff vertebrae of modern marlins.
"I think it must help with stiffening the body, because the tail is so flexible," Sallan said. "If you look at the general shape, it's more like a tadpole or an early tetrapod, so it might just function to hold the body steady because the tail is flapping."
|Contact: Rob Mitchum|
University of Chicago Medical Center