As many regular readers may have surmised, my son Tim is homeschooled, which is how he’s able to spend so much time in the field with me. As part of his science education he’s required to do various projects (some of which are on his blog), and as his most recent on is on paleontology I decided to post some of his results here.
There’s some interesting potential for studies on Carmel Church sharks, because there are large numbers of teeth that all come from a single stratigraphic horizon and small geographic area, so they may represent a true living population much more closely than do most shark tooth samples.
Tim looked at the two species of tiger sharks found at Carmel Church, Galeocerdo contortus and Galeocerdo sp. Shark tooth fans may know G. sp. as G. aduncas, but Purdy et al. (2001) make the case that G. aduncas is a nomen dubium. In the images at the top G. contortus is on the left and G. sp. is on the right. There is an easy identification feature that separates these species – the shape of the anterior cutting margin is distinctly wavy only in G. contortus (on the left below):
One interesting point with these two species is that (according to Purdy et al.) they are always found together, and that (at least at Lee Creek Mine) they occur in a 2:1 ratio with G. contortus being the more common of the two. Tim’s Carmel Church sample confirms this ratio.
Tim also confirmed what I had long suspected, that G. contortus tends to be larger (or at least taller) than G. sp. (at least at Carmel Church):
I’m not sure what this indicates, other than that these teeth are quite different from each other (maybe they should be different genera!). Tim speculates that maybe the prey preferences of G. sp. didn’t change as the shark grew (so no change in tooth thickness), while perhaps older, larger G. contortus fed on different, larger prey than juvenile G. contortus.
Tim’s complete report is available on his blog; I encourage you to check it out.