Juan Cisneros, Domingas de Conceiçáo, and Martha Richter examine a newly discovered fossil shark spine. Photo by Ken Angielczyk.
In my previous entry, I noted the difficulties that sometimes accompany efforts to relocate historical fossil localities. Today, I would like to describe an instance when using a combination of the scientific literature and new technologies worked to help us find fossils.
One of the main scientific papers that we're using in our efforts is one published by Dr. Barry Cox and others in 1991. This paper describes fossils he and his collaborators found in the area near Pastos Bons and Nova Iorque in 1970 and 1972. In the paper they provided information on what level in the local rock sequence they found their fossils, as well as where they found them in terms of a distance from Pastos Bons along the road to Nova Iorque and a distance away from the road. Barry also graciously sent me some photos from his work in the area, so we have an idea of what the actual outcrops look like and how the fossils are exposed on the surface. Unlike most of the fossils we found in the quarry, which were still embedded in the surrounding rock, Barry's specimens were found loose on the surface.
Based on Roger Smith's work over the last few days, we now have a good idea of the local sequence of rocks (or stratigraphy) of the area, as well as how exposures of those rocks tend to be situated relative to local geographic features, such as ridges or river beds. So, our first step was to determine how the rocks Barry described fit into our picture of the local stratigraphy. Once we had done that, we could make a prediction about where exposures of those rocks might occur geographically.
To refine our prediction, we went onto Google Earth and examined satellite photos of the region near Nova Iorque. Working from areas that we had visited and in which we knew the rocks, we determined a general area where the target rocks were likely located. Then, we looked at the satellite images in detail to find exposures of rock in the area of interest. We also double-checked this location to see if it was about the right distance down the road and about the right distance from the road to correspond to Barry's fossil localities. Finally, we obtained latitude and longitude coordinates from Google Earth for the outcrops we could see. We entered these into our GPS receivers, and then it was off to the field.
It was just a short walk from the side of the road to the exposure, and our GPS receivers pointed the direction we needed to go to reach the outcrop. Within a few minutes of arriving, we had found a fossil shark spine. Things don't usually go quite this smoothly, but it does provide a good example of one of processes we use to reconstruct this kind of information and how things happen when everything goes right.
Fossil shark spine found loose on the surface of the outcrop we targeted using Google Earth. Note that the ornamentation of the spine is similar to one that we found a few days earlier in the quarry. Scale bar is in centimeters. Photo by Ken Angielczyk.
In addition to finding the shark spine and other fossils at the locality, this exercise was important for another reason. The preservation style of these fossils and how they appear on the surface is somewhat different than most of the fossils we have discovered so far on this trip and on our reconnaissance trip in 2011. So we now have a new search image to use for finding fossils in the area, and one that we think will be very useful. Just before we returned to our houses, we stopped at a similar outcrop to the one at which we found the shark spine that we visited briefly in 2011. We didn't find much last time, but with the new search image, we found some very exciting fossils. In particular, Jörg Fröbisch discovered a small piece of a lower jaw with two teeth that seems to belong to Prionosuchus plummeri, the large fossil amphibian known from the Parnaíba Basin. Although we've found other specimens that seem to belong to amphibians on this trip, this is the first one we can say with some certainty represents Prionosuchus. Tomorrow, our plan is to return to this area to see if we can find more because our searching was suspended on account of darkness.
Jaw fragment of the temnospondyl amphibian Prionosuchus plummeri. The photo is taken looking down at the two broken teeth. Scale bar is in centimeters. Photo by Ken Angielczyk.