The study of a new species of coelacanth from the Middle Triassic period, with a strange morphology for these fish known as “living fossils,” shows the formation of many species in a short time, after a mass extinction that occurred 252 million years ago, with more than 80% of marine species lost.
Researchers from the Museum of Natural History in Geneva and the University of Geneva (UNIGE) compared the fossils discovered in the Grisons and in Ticino. Their findings are published in the journal Scientific reports.
Coelacanths are strange fish that are currently only known from two species found off the coast of East Africa and Indonesia. Their fins, among other characteristics, show that these animals are closer to terrestrial vertebrates, including humans, than to other fish. So they give an idea of the appearance of the fish ancestor of our species. During the 420 million years that the coelacanth line existed, the various species evolved slowly, earning them the nickname “living fossils.”
A few years ago, two coelacanth fossils, discovered in Triassic rocks in the Grisons region of eastern Switzerland, turned out to belong to a new very different-looking species, Foreyia maxkuhni, with a very short body and a domed skull.
This first discovery prompted researchers to look at other coelacanth fossils discovered at the UNESCO World Heritage site of Monte San Giorgio in Ticino (Italian Switzerland). These fossils are the same age as those from the Grisons. These specimens were discovered in the middle of the 20th century and are preserved in the Paleontological Museum in Zurich. They have never been studied in detail because of the difficulty of interpreting them.
A new species of coelacanth
During his doctoral thesis, Christophe Ferrante, a researcher at the UNIGE Faculty of Science, showed that this is a new species of coelacanth, evolutionarily very close to the species from the Grisons, named Rieppelia heinzfurreri. Some characteristics of this species are similar to Foreyia while others are strangely reversed: one has small front fins and another has large ones, one has small opercles and another has giant ones, etc.
This study shows that these two species (as well as two others with a more classic morphology) are part of a small evolutionary radiation, ie the formation of some species in a short time and a small space. This phenomenon can be seen in some groups of organisms but it is known for the first time in coelacanths.
The largest mass extinction of the last 500 million years occurred 252 million years ago, with over 80% of marine species lost due to massive volcanic eruptions in Siberia. The amazing Swiss coelacanths, which lived about 10 million years after this catastrophe, show that they can still take advantage of the special conditions of the post-extinction environment on Earth to become unique forms in their history. These niches were later reinvested by other groups, including all the major groups of bony ray-finned fishes that still occupy them today.
Lionel Cavin’s team at the Natural History Museum in Geneva continues to study these strange postapocalyptic coelacanths from the Triassic by describing new fossils discovered in different places around the world and by looking at the potential genetic characteristics of the origin of these unusual forms based on the comparison of the genomes of present-day vertebrates.
Christophe Ferrante et al, Early Mesozoic explosion of morphological disparity in the slow-evolving coelacanth fish lineage, Scientific reports (2023). DOI: 10.1038/s41598-023-37849-9
Given by the University of Geneva
Citation: Fossil study shows that coelacanths flourished in Switzerland after a mass extinction (2023, July 20) retrieved on July 20, 2023 from https://phys.org/news/2023-07-fossil-coelacanths-switzerland-mass-extinction.html
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