Roger Smith examining the rocks forming the wall of a quarry just outside of the town of Timon, a suburb of Teresina. Photo by Ken Angielczyk.
Today was our first day of fieldwork in the Teresina area this year. We decided we would return to the quarry outside of the town of Timon where we found a very interesting fish skull last year. We're just starting to prepare that specimen, so I can't offer many details about it at this point, but it certainly seems to have a lot of potential. Based on that specimen, our expectations were high and the quarry did not disappoint.
Not long after arriving today, Martha Richter literally stumbled across a partial skeleton of a terrestrial vertebrate (or tetrapod) preserved in a few pieces of rock in one of the quarry spoil piles. The main layer of the quarry that is used for paving material is the hard red siltsone that forms much of the vertical walls. However, at the base of the wall and exposed in some other areas is a softer sandstone that is too friable to use for paving, hence the reason that pieces of it are mostly discarded. It's not an exaggeration to say that this specimen is the most exciting that we've found in our two years of fieldwork in the Parnaíba Basin.
Partial skeleton of a tetrapod from the quarry in Timon. The skull is in the upper left portion of the picture. The large, white pieces of bone just behind the skull are likely parts of the animal's shoulders, and parts of vertebrae (or backbones) can be seen extending towards the bottom of the picture. The scale bar is in centimeters. Photo by Ken Angielczyk.
So what is it? First, I'll say that it's not a synapsid. That's a little disappointing, but the specimen is interesting enough that it's easy to get over. Instead, the specimen appears to represent a type of amphibian. As you can see, the specimen has a fairly short, broad skull that lacks the very elongate snout of Prionosuchus. Therefore it is definitely something new to the basin. The size and shape are a bit reminiscent of the little jaw fragment that Domingas found a few days ago, so it might represent that animal. More preparation of both specimens will be necessary to definitely say whether that's the case. Beyond that, there was a lot of discussion of which group of amphibians the specimen might be part of, based on our attempts to interpret the anatomy exposed in the specimen. A couple of our guesses focused on two groups, the microsaurs and the amphibamids. Both are known exclusively from areas in the northern hemisphere during the Permian, so finding one south of the paleo-equator would be an important discovery. Again, more preparation of the specimen will be necessary to be sure, and we're all already thinking about what might be the best ways to approach this process. Every specimen is a unique problem when it comes to preparation, and the way this one is preserved suggests it will require a particularly delicate touch.
Luckily, the excitement of finding the skeleton was enough to keep us motivated for they rest of the day. It was very hot today (even by local standards), and the only other fossils we found in the quarry during the rest of our searching were small, unidentifiable fragments of bone. The plan for tomorrow is to do more prospecting for fossils in a couple of other quarries in the area. Our discovery today has given us an idea of what rock layer will be good to target, and it would be great if we can find more material like this.