This time we have a guest blog post from the TW:eed Team’s Rob Clack, about his recent volunteer lab work uncovering fossil bones!
As I’m retired and enjoy preparing fossils, it’s a pleasure for me to spend a day a week helping out in Jenny’s lab in Cambridge. Over the years, we’ve accumulated quite a lot of rock samples by doing what we term ‘bulk collecting’. This means looking at beds we know have yielded fossils in the past, and gathering lumps that show nothing, in the hope that when we break them up in the lab, we’ll find something interesting.
Some time ago, I started looking at material like this that we’ve collected from quite high in the Ballagan Formation sequence. This particular fossil-rich bed has already yielded a large rhizodont cleithrum (see photo) and the partial lower jaw of a large tetrapod called Crassigyrinus, a secondarily aquatic animal with minute legs, as well as large lungfish bones. Almost everything we find is disarticulated, which is to say that the animal died, its flesh rotted away and the bones came apart before being buried and subsequently fossilised.
|Large rhizodont cleithrum (shoulder element), scale bar 1 cm|
Most of the time, I use a mounted needle to pick the matrix away by hand, watching what I’m doing down a binocular microscope, with an air pump blowing across the specimen to shift the tiny bits of rock I’m picking off. For the harder rock, I use a dental mallet. This has an electric motor hanging from a stand above me, with a flexible drive coming down beside me. On the end is a handpiece which translates the rotary motion of the motor into a reciprocating movement to power a needle in a tiny forward-and-backward motion.
Usually, after I’ve exposed a small area of bone, I soak it in consolidant consisting of a clear plastic dissolved in acetone. This penetrates all the little cracks in the bone and glues them together, so they don’t blow away as I expose more bone. One advantage of this is that if I get it wrong and a piece of the bone moves, I can dissolve the consolidant with more acetone, and move the fragment into the right position.
Rob Clack at work preparing fossils in the lab
The lumps of rock we’ve got are not huge, so I’m unlikely to find anything as big in the lab as we did in the field, but even so, there is quite a lot there, just waiting to be found. A month or two ago, I found a small tetrapod jugal bone. This is a cheek bone that sits behind the eye, forming part of the margin of the orbit
More recently, I’ve found skull bones of several small lungfish, a hyomandibular bone (connected the jaw articulation to the braincase, strengthening the skull) of a rhizodont fish, as well as several other rhizodont bones, part of the skull table of a tiny tetrapod, and yesterday, an intriguing small bone, less than a centimetre across, covered with tiny denticles. We don’t know what sort of animal it came from, but it is unlikely to be a lungfish, since they didn’t have normal teeth, just bony plates with radially-arranged conical ridges.
I’ve also found plenty of fish scales of various sizes and types, spines, and quite a few skull bones which are in internal view, making them very hard to identify. They’re too fragile to lift entirely off the surface of the rock, so we may never know what animal they came from.
On the other hand, one day we might find a more robust one that we can turn over, and then we’ll be able to say “Oh, it’s one of those!” and slot another piece of the jigsaw into place.
Wow, I wish I was working there, how wonderful!
Until next time