Rare fossils provide a more detailed picture of biodiversity during the Middle Ordovician

A series of marine fossil specimens discovered in northern Portugal that lived between 470 and 459 million years fills a gap in understanding the evolution during the Middle Ordovician period.

The discovery, explained in a new article that has just appeared in The science of nature, details three fossils found in a new "Burgess shale-type deposit". (Burgess Shale is a well-known deposit in Canada among evolutionary biologists for its excellent preservation of soft-bodied organisms that do not have a biomineralized exoskeleton.)

"The document describes the first soft-bodied fossils preserved in the form of Portuguese carbon films," said senior author Julien Kimmig, head of collections at the University of Kansas Institute of Biodiversity. and the Natural History Museum. "But what makes it even more important is that it is one of the few deposits that date back to the Ordovician period – and more importantly, they come from the Middle Ordovician, a time when very few soft-bodied fossils are known. "

Kimmig and his colleagues at the KU Biodiversity Institute, undergraduate researcher Wade Leibach and senior curator Bruce Lieberman, as well as Helena Couto from the University of Porto in Portugal (who discovered the fossils), describe three fossil specimens sailors: a medusoid (jellyfish), a possible wiwaxiid sclerites and an arthropod carapace.

"Before that, there was nothing found in the Iberian Peninsula in the Ordovician that looks like this," Kimmig said. "They fill a gap in time and in space, and what is very interesting is the type of fossils we find Medusozoa – a jellyfish – as well as animals that seem to be wiwaxiids, which are armored molluscs resembling whales, which have large spines, lateral sclerites of animals that were thought to have extinguished at the end of the Cambrian (some may have survived in the Ordovician in a Moroccan deposit), but nothing concrete has ever been published on them: those who are really in the middle of the Ordovician, which incredibly widens the range of these animals. "

Kimmig said that the discovery of rare wiwaxiids fossils during this period suggests that animals have lived on Earth for a much longer period than previously understood.

"Especially with rather rare animals that we do not have today like wiwaxiids, it's nice enough to see that they've lived longer than we ever thought," did he declare. "Right after this deposit, in the Upper Ordovician, we have a significant extinction event, so it is likely that the wiwaxiids survived until this extinction event and did not occur. not extinguished earlier because of other circumstances.But it could have been any matter caused the Ordovician great extinction event killed them, too. "

According to the researchers, the soft-bodied specimens fill a gap in the Middle Ordovician fossil record and suggest that "there remains many soft-bodied fossils in the Ordovician, and a fresh look at shale and deep water slates of this period is justified. "

"It's a very interesting thing with these discoveries – we're actually getting a lot of information on the distribution of animals chronologically and geographically," Kimmig said. "Plus, it gives us a lot of information on how animals have adapted to different environments and where they have managed to live.With these soft body deposits, we have a much better idea of ​​the number of animals." Animals and how their environment has changed This is something that applies to modern times, to climate change and to changes in water temperature, because we can see how animals, in the geological, adapted to longer periods.

Co-author Couto discovered the fossils in the Valongo Formation in northern Portugal, a region known for containing trilobites. When the animals were alive, the Valongo Formation was part of a shallow sea on the fringes of northern Gondwana, the primitive supercontinent.

"Based on shellfish fossils, the deposit appears to be a fairly common community of the Ordovician," Kimmig said. "And now we know that in addition to these common fossils floating in jellyfish, we had slug-like molluscs lurking on the ground, we also had larger arthropods, which could have been predators. a much better picture with these soft-bodied fossils of what these communities actually looked like. "

According to the KU researcher, scientists until recently did not understand that deposits from this period could preserve soft-tissue specimens.

"For a long time, it was simply not known that these types of deposits had survived until the Ordovician," Kimmig said. "So, it is likely that these deposits are more common in the Ordovician than we know, it's just that people have never searched for them."

Kimmig led the analysis of fossils at KU's microscopy and analytical imaging laboratory to ensure that the fossils were made of organic matter. Leibach, an undergraduate researcher at KU, did a lot of the lab work.

"We analyzed the material and examined the composition, because sometimes you can get pseudo-fossils, minerals that create something that looks like a fossil," said Kimmig. "We had to make sure that these fossils had an organic origin, and what we discovered was that they contain carbon, which was the main indication that they would actually be organic. "