Brazil had seas full of invertebrates during the Devonian Period

Mollusks known as tentaculitoids lived 400 million years ago in the icy seas that then covered part of what is now Brazil.

By Peter Moon  |  Agência FAPESP – Many people think of dinosaurs when they hear the word ‘paleontology’, and others imagine mammoths or saber-toothed tigers. But does anyone picture mollusks and invertebrates? “Little is said about invertebrates in Brazil,” said Jeanninny Carla Comniskey, a researcher currently studying for a PhD in paleontology, adding that paleontologists “suffer” from a lack of interest in invertebrates and the small number of professionals in the field. Comniskey specializes in tentaculitoids, a class of calcareous tube-forming organisms that lived during the Devonian Period 400 million years ago in the gelid seas covering part of what is now Brazil. The land mass was then close to the South Pole.

“Research published in the Northern Hemisphere generally does not even mention the existence of tentaculitoids in Brazil or South America,” Comniskey said, blaming the ‘traditional theory’ for this omission. “Paleontologists who follow the traditional theory believe there could not be any tentaculitoids here because the water was too cold and because significant diversity among genera and species would be impossible. Although it is true that we have few genera compared with the north, they appear in large quantities and in many different outcrops.”

Not only did tentaculitoids exist here, according to Comniskey, but they were plentiful. Indeed, there have been finds in Argentina, Bolivia, Brazil, Peru and Uruguay. In Brazil, the most abundant and well-known are fossils from the Paraná Basin.

Comniskey undertook the first systematic review of species found in the Amazon and Parnaíba Basins. “The aim was to study all holotypes,” she said. A holotype is the specimen designated as the type of a species by the original author who named and described it.

She analyzed 39 samples from scientific collections, comprising 153 specimens dated to the Middle Devonian (34 from the Amazon Basin and 119 from the Parnaíba Basin). She was able to verify the occurrence of five species, fewer than the seven species found in the Paraná Basin.

The study is part of “Macroinvertebrates of the Brazilian Devonian and their paleobiogeographical affinities,” a special volume published by Boletim do Museu Emílio Goeldi, Ciências Naturais, and provides an overview of current knowledge about Brazilian Devonian tentaculitoids. Comniskey is affiliated with the University of São Paulo’s Ribeirão Preto School of Philosophy, Science & Letters (FFCLRP-USP). Her research is supported by FAPESP.

“Little is known about the animal residing in the shell,” Comniskey said. Tentaculitoids lived in a long, thin, cone-shaped shell, which could be smooth or ribbed, measuring approximately 1.8 cm. “It is believed that tentacles emerged from the tip of the shell – hence the name. These animals lived at the bottom of the sea, but we do not know if they were solitary or colony forming.”

The shells found to date are the only fossils recording the existence of tentaculitoids, which disappeared 360 million years ago in the mass extinction that ended the Devonian. “There is a school of thought that tentaculitoids display an affinity with worms,” Comniskey said, “but I believe they have more affinity with mollusks.”

Comniskey compared the seven species from the Paraná Basin with the five species from outcrops in the Amazon and Parnaíba Basins. “You can see that they are different species just by looking at them,” she said. “Shell size and shape differ, as does rib thickness.”

The Paraná Basin species are older, from approximately 410 million years ago; the species from northern Brazil lived some 380 million years ago. “This suggests the Paraná Basin may not have been in contact with the other two basins, at least during the Devonian,” Comniskey said.

In addition to freezing water, another reason the existence of this class of marine invertebrates in Brazil is practically unknown to scientists elsewhere is their state of conservation. Tentaculitoid fossils in Brazil leave much to be desired compared with those from other regions. “They have been so poorly conserved that the material is often fragmented and flattened or compressed,” Comniskey said. The problem may have to do with the anatomy of these distant cousins of mollusks. A tentaculitoid’s shell or conch is divided into four parts: the embryonic chamber, the juvenile region, the adult region, and the aperture, from which the tentacles protruded.

“In most cases, only the adult part and aperture have been found,” Comniskey said. “The fossils occur in sandstone and siltstone, suggesting that the animals may have lived both in shallow waters near the shore and in a deep-water or benthic habitat.”

Thus, far from not existing, Brazilian tentaculitoids were diverse in terms of genera, and this diversity is growing: Comniskey recently submitted another paper describing seven new species from the Paraná Basin for publication in the journal Zootaxa.

The Age of Fish

The Devonian is known worldwide as the “Age of Fish.” It was a period during which fish evolved and ruled the oceans. They included the magnificent Dunkleosteus, a predatory fish covered with bony armor that could grow to be 10 meters long. The first sharks also evolved in this period. However, no vestige of any fish has ever been found in Brazilian rocks, with only shells being present. The only find reported in in South America was in Bolivia. “My dream is to find fish fossils from the Devonian in the Paraná Basin,” Comniskey said.

For at least 40 years, researchers have been looking for fish fossils from the Brazilian Devonian. “No one has found anything. If they existed, we would have found them by now,” said Renato Pirani Ghilardi, a professor of paleontology at São Paulo State University’s Bauru School of Sciences (FCB-UNESP) in São Paulo State. Ghilardi co-edited the volume on macroinvertebrates of the Brazilian Devonian.

“We think there is a conservation problem in Brazil’s Devonian basins. The climate and geology, as well as the conditions in the region’s oceans, did not contribute to the survival of fossils. Fish skeletons are composed of phosphate, whereas invertebrates’ shells are made of chitin and carbonate. Apparently, phosphate-based fossils simply can’t last,” Ghilardi said.

The first expeditions to collect Devonian material in Brazil took place at the turn of the nineteenth to the twentieth century. Little of this material has been studied. “For example, the National Department of Mineral Production, DNPM, has boxes and boxes of fossils that have never been opened,” Ghilardi said. The reason is simple: there are not enough invertebrate paleontologists. Brazil has dozens of vertebrate paleontologists but “only seven or eight invertebrate paleontologists working in higher education and research institutions.”

Although few in number, these researchers are unearthing an impressive picture of biodiversity for the Brazilian Devonian. Along with tentaculitoids, some 15 species of trilobites, a vast group of extinct arthropods, existed; other types of animals included cnidarians (represented in the present by jellyfish), bivalve ancestors of the mussel, and ten species of brachiopods, which are small benthic animals with a soft body enclosed in two shells.

Overall, the state of conservation is poor. “It is impossible to perform electron microscopy because the skeleton has not been conserved, only the animal’s outline,” Ghilardi said. “However, by studying the rocks in which fossils were found, we can infer things such as water temperature, dissolved oxygen level, and even whether there was volcanic activity. This tells us whether the water was cold and the environment anoxic, meaning oxygen-free, in the areas where the animal lived.”

The Kacak Event, a very important phenomenon that occurred during the Devonian, can be identified in Brazilian fossils. “The Kacak Event killed off many species,” Ghilardi said. “The survivors were much smaller and are known as Lilliput fauna” after the island in Gulliver’s Travels.

Fossils of small plants and a few insects are also found in rocks of the Brazilian Devonian. “Macroscopic life began spreading across the continents in the Devonian,” Ghilardi explained. “Plants and insects were the pioneers.”

Far more research on Devonian biodiversity in Brazil is needed, especially in terms of paleobiology and biogeographic relations. “We should stop doing armchair paleontology and start trying to understand the evolutionary links among all these animals. We need to start doing twenty-first century science,” he said.

The article “Current knowledge about Devonian tentaculitoids of Amazonas and Parnaíba basins, Brazil, deposited in Brazilian institutions” by Comniskey, Ghilardi and Elvio Pinto Bosetti from Paraná’s State University of Ponta Grossa (UEPG), published in Boletim do Museu Emílio Goeldi, Ciências Naturais, can be downloaded as a PDF file from www.museu-goeldi.br/editora/bn/artigos/cnv10n1_2015/conhecimento(comniskey).pdf. “Macroinvertebrates of the Brazilian Devonian and their paleobiogeographical affinities” can be found at www.museu-goeldi.br/editora/naturais_en/index_en.html.