This past Monday, during an outing to a quarry with Dave Broussard, our very own Tim (Fossildude19) and Paul (Paul1719) in PA. I found a partial ischnacanthid fish jaw. As it was only the second known from that location I donated it to Dave for study. A few moments later Paul found one too! He also donated his. It was interesting and enlightening watching a professional photograph and preserve it before removing the part of the slab it was in. Dave is a professor at Lycoming College in PA. and a vertebrate paleontologist.
Ischnacanthids had a primitive arrangement when it came to teeth (though some argue it was more advanced than we give it credit for.) The teeth were a part of the jaw, though still made from the dentin bone material in the jaw. They did not appear to be able to regrow them as far as we know. This specimen has two partial teeth and one complete one. Im hoping to read Dave's research on the subject when he publishes it.
The photo is courtesy of and copyrighted Dave Broussard.
*I accidentally put Acanthodians had a primitive arrangement..I meant ischnacanthids ( a type of acanthodian.)