One of the issues with collecting at Carmel Church is that, once exposed to air, the fossils weather at a spectacular rate. Within days gypsum will start to grow on the surface, and over the next few months the bones will develop an extremely hard sediment crust on their outer surface. By this point anything that’s small and delicate is lost for good, as the bone under the crust deteriorates (that’s assuming we find it in the first place; encrusted bones are hard to spot). Tougher items, like shark and ray teeth, and some fish and large whale bones, can survive a little longer, but even they eventually will be lost.
We still collect encrusted, weathered bones when we spot them. It’s often difficult to tell what’s underneath the crust, and there’s always the possibility that we’ve gotten to it early enough that it’s not too badly damaged. Last month, Mike Morriss found the specimen shown above in the weathered material, which appeared to be a pretty complete ray tooth battery. These are quite rare; we’ve found about a half-dozen at Carmel Church, and they’re much more common there than at most other sites. So we brought this one back home, in the hope that it had survived.
The crust is generally harder than bone, and is difficult to remove. Over a couple of weeks (about 12 hours of actual cleaning time) volunteer Kathy Fell and I used a MicroJack to remove as much of the crust as possible. Here are the results:
Not bad, and in fact much better than I had initially feared. The hard occlusal surface (which is what’s visible here) was etched from weathering, but the individual tooth plates are still visible, including the small diamond-shaped plates along each side. The other side, which is much softer, is not as well preserved.
There is some debate about exactly which type of ray this type of tooth battery represents, and various names have been assigned at different times. Current consensus seems to be that these are bull rays of the genus Pteromylaeus. This is an upper dentition; although it’s not obvious in this photo, the battery is strongly arched front-to-back (front is at the top). A corresponding lower dentition would be nearly flat (here’s an example of the in-place dentition in a modern specimen of Pteromylaeus.) These are the most common non-reworked rays at Carmel Church, and we actually now have four nearly complete batteries from this genus (two uppers and two lowers).