Farewell to Nova Iorque

Ken Angielczyk, an assistant curator at the Field Museum of Natural History, is searching for fossils of ancient mammal relatives in northeastern Brazil.

Monday, April 23

Today was our last day of fieldwork in the Nova Iorque area. Tomorrow we will head back to Teresina to spend a few days working on rock exposures near the city. Last year we found a couple of interesting fossils there in just a couple of hours of prospecting, so we think it’s important to make sure we revisit those localities. However, the exposures there are not as extensive as those near Nova Iorque, hence the reason we spent so much time here this year.

Because we’re leaving this area, it’s natural to reflect on what we accomplished. We didn’t find the synapsids we were hoping to discover. This might stem from the environments represented by the rocks being inhospitable to synapsids. Alternatively, it might mean that synapsids had not yet dispersed away from the equatorial regions at the time the Pedra de Fogo Formation was being formed. Or we may just have been unlucky. But when I think back to our time here in comparison to our trip in 2011, it’s clear that we’ve made progress.

One of our most important accomplishments has been to gain a better understanding of the rocks in this area, and the number of fossil-bearing levels present within them. We didn’t have a good concept of this last year, but thanks to Roger Smith’s work this year, we’ve concluded that there are about 12 levels in the Pedra de Fogo Formation that preserve fossils, most of which are in the bottom half of the formation. With this new understanding, we’ve been much more successful at targeting outcrops that are likely to produce fossils while avoiding those that are likely to be barren. In turn, we’ve collected a lot more material, representing a greater diversity of animals, than we did last year. In particular, we’ve found a lot more amphibian material this year. We think there might be as many as four species of amphibian present, instead of just Prionosuchus plummeri as was known previously. We also found likely new species of sharks and lungfish, so we’re definitely getting a better picture of the animals that were living here during the Permian.

As we study these fossils more, and compare them to specimens known from elsewhere in the world, we should be able to get a better picture of the relative age of the Pedra de Fogo Formation and the formation’s implications for the distributions of animals on the supercontinent of Pangea. At the moment, the environment represented by the rocks, the diversity of amphibians, and the lack of synapsids make the Pedra de Fogo community seem similar to the community of animals known from the Permian of Niger, which was at roughly the same latitude but somewhat to the east at the time. The Niger community is relatively unusual among those known from the Permian, so if the Pedra de Fogo animals are similar, then it might imply that central Pangea hosted an assemblage of animals unlike those known from near the Equator or at higher latitudes. The comparison isn’t perfect because there are reptiles known from the Permian of Niger, and we have not found any reptiles in the Pedra de Fogo Formation (despite seeing some of their living relatives).

As is often the case in science, although our research is answering some questions, it’s also raising others, and I don’t think we’ve exhausted the potential of the Pedra de Fogo Formation. For example, there’s areas to the west of Nova Iorque that we visited last year but ignored this year. Last year, we were uncertain exactly how the rock sequence fit with the sequence near Nova Iorque, and I would be quite interested to see how Roger’s framework holds up there. We will be able to see how it fares near Teresina in the next few days. Hopefully I will have interesting new fossils to tell you about when we start work there.