09.01.2019 aktualizacja 09.01.2019

We know more about how ichthyosaurs breathed

Some ichthyosaurs - the great predatory marine reptiles that lived in the times of the dinosaurs - had their snouts constantly open. That is how they exhaled the air collected inhaled when they emerged, determined palaeobiologists from the Polish Academy of Sciences. Until now, the breathing of these animals was a scientific mystery.

The new findings were made after reanalysing the fossilized ichthyosaur skull discovered in the Morawica quarry, about 18 km south of Kielce. The remains date back around 155 million years. They were discovered 20 years ago, but scientists decided to look at the specimen again. The olfactory chamber drew their attention.

"The construction of this chamber and its comparison with the olfactory chambers of other ichthyosaurs indicates that the reptile was swimming with a completely or slightly open snout, thus exhaling the air" - told PAP one of the authors of the discovery, Dr. Daniel Tyborowski from the Polish Academy of Sciences Museum of the Earth. The remaining researchers are from the Institute of Paleobiology of the Polish Academy of Sciences - Piotr Skrzycki and Marek Dec. Researchers note that the ichthyosaur breathing has not been comprehensively studied. They are among the first to investigate this issue. The publication on the subject appeared in the British journal Historical Biology.

According to the researchers, the method of breathing of the studied ichthyosaur is unusual for aquatic reptiles and mammals. Crocodiles and whales breathe completely differently, they swim with closed snouts. Immediately after inhaling the air, their nostrils are blocked - so that water does not enter the inside of the skull. When these animals want to exhale, they must emerge.

"Meanwhile, ichthyosaurs did not have a blocking mechanism for their nostrils. Therefore, after breathing in on the surface and submerging, the water would flow into the nostrils. Slightly open snout was its only exit. These animals breathed out the same way. They did not do it as spectacularly as whales" - says Tyborowski. He notes that it is uncertain whether all ichthyosaurs breathed the same way.

According to the researcher, the examined specimen had a large olfactory chamber, which may indicate a highly developed sense of smell.

"Ichthyosaurs had large eyes that occupied the entire surface of the skull - this sense was certainly very useful in the deep sea, and we know that these animals could dive to 500 metres, but the sea in the area of today`s Kielce about 150 million years ago was shallow. The sense of smell could be more important when hunting" - says Tyborowski. According to the researcher, ichthyosaurs living in shallower waters could be adapted to life differently than those penetrating deep waters in other parts of the globe.

"Ichthyosaur`s eyes draw attention because they are huge. Many articles on them have been published, but other senses have been neglected" - Tyborowski notes.

The use of the sense of smell was possible because the reptile`s nostrils remained open. Even underwater, ichthyosaurs could still use the sense of smell. Meanwhile, for example, crocodiles that close their nostrils shortly after immersion and can only use their eyes to track their prey.

The individual from Morawica reached a length of about 7 m. The researchers also found that it had powerful teeth that it could use to successfully attack large fish, birds and even turtles.

Ichthyosaurs were sea reptiles that resembled a shark-dolphin hybrid. Only a few fragments of fossilised skeletons of these animals are known from Poland. These sea giants preyed in the seas about 251 to 90 million years ago. Ichthyosaurs discovered on the Vistula River are the largest known predators from the times of the dinosaurs.

A fragment of the ichthyosaur skull from the Morawica quarry was discovered accidentally. The quarry is the source of limestone often used as material for floors or sills in public buildings. workers alerted the researchers that a prehistoric animal skull outline was visible in one block of limestone. The block is currently in the collection of the National Museum in Kielce.

PAP - Science in Poland, Szymon Zdziebłowski

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