Tooth of Anisopleurodontis pricei discovered by Mayana de Castro Silva, an undergraduate student who is working at the Federal University of Piauí with Juan Cisneros. Photo by Ken Angielczyk.
In a previous post, I noted that many of the fossils we find are the remains of sharks that lived in the Parnaíba Basin. Yesterday and today we found several teeth in the course of our work that are both very impressive and are representative of a group of sharks that many people are unaware of, even though members of the group persist today.
The Holocephali are known by several common names, including ratfish and chimeras. The latter name is especially fitting because members of the group often look like they were put together from a random assortment of spare parts from other sharks and bony fish. Most chimeras in the modern biota live in deep ocean waters and or of limited economic importance, so they are infrequently seen by the general public.
One species of fossil chimera, Anisopleurodontis pricei, is known only from the Permian of the Parnaíba Basin. We didn't find any fossils of it on our trip in 2011, but this year we've been finding a lot of them, perhaps because we're looking for fossils in a slightly different way. Mayana de Castro Silva, and undergraduate student working with Juan who is on the trip started the flood yesterday when she found a beautifully preserved isolated tooth. Christian Kammerer followed up this afternoon by finding a set of several teeth that likely belonged to one individual. Even Jose, one of our drivers who likes to look for fossils, got in on the action when he found a tooth embedded in the rock forming the floor of a stream bed.
A tooth of Anisopleurodontis pricei that is part of a set found by Christian Kammerer. Note the elaborate ridged ornamentation on the base of the sides of the teeth. Photo by Ken Angielczyk.
Like most sharks, the majority of the skeleton of Anisopleurodontis pricei was composed of cartilage; therefore we only know it from its teeth. Chimeras tend to have relatively large heads for their body size, so it's likely that Anisopleurodontis pricei was in the range of two to three meters long in life, even though its teeth are impressively large. Many chimeras known from the Permian seem to have had diets consisting of hard-shelled prey, like bivalves, snails, brachiopods, and ammonoids (shelled relatives of squid and octopods that resembled the living chambered nautilus). However, they tend to have broad, flattened teeth suitable for crushing, unlike the taller, concical teeth of Anisopleurodontis pricei. This might mean that Anisopleurodontis pricei had a diet that included animals like fish that it could puncture its teeth. On the other hand, some of the teeth we found today have wear facets on them, which formed when the teeth were rubbing against resistant parts of prey, so maybe Anisopleurodontis pricei was something of an omnivore, eating both fish and hard-shelled prey.
We also have been having good luck finding tetrapods over the last couple of days. So far they are all amphibians, but we've found a mixture of skull and jaw bones, as well as parts of the limbs. Most of these seem to represent Prionosuchus, but one little specimen that was found by Domingas da Conceiçáo (another undergraduate working with Juan who was also on the 2011 trip) seems to represent a new kind of amphibian. Its small size, combined with the fact that the curvature of its jaw is indicative of an animal with a much shorter, broader skull than Prionosuchus implies that is something different. If further study does confirm that the specimen is not Prionosuchus, it will be only the second species of terrestrial vertebrate known from the Pedra de Fogo Formation, and thus an important discovery.
Small amphibian jaw that might represent a new species from the Pedra de Fogo Formation. The picture shows the top surface of the jaw, with the broken surface of the teeth. Photo by Ken Angielczyk.