A new genus and species of fossil brittle stars have been identified

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Brittle stars, animals with five-segment radial (pentaradial) symmetry, lived millions of years ago in the territory of present-day Poland. They survived, although today they can only be found in high salinity waters. Fossil species of these agile echinoderms found in Kujawy and the Krakow-Częstochowa Upland have been described by scientists from Warsaw.

A new genus and species of fossil brittle stars – Ophiobartia radwanksii – have been identified by Dr. Michał Loba from the Polish Academy of Sciences Museum of the Earth in Warsaw and Dr. Urszula Radwańska, a professor at the University of Warsaw. The article presenting discoveries from the two of the Upper Jurassic (Oxfordian and Kimmeridgian) locations: from the sites Wapienno/Bielawy in Kujawy and the Zalas quarry in the Krakow-Częstochowa Upland, appeared in Acta Geologica Polonica.

Brittle stars (Ophiuroidea) are the less known cousins of starfish. Together with them, as well as sea cucumbers, crinoids and sea urchins belong to echinoderms (Echinodermata). Echinoderms are very specific animals that live only in seas, the scientists explain in the Museum of the Earth press release.

“Brittle stars use snake-like movements of their arms to move and catch their prey. For echinoderms, they are quite agile. The occurrence of ambulacral legs in modern species is most often limited to the central disk and the initial section of the arms. These animals can be considered predators. But do not imagine a spectacular pursuit of the prey – brittle stars hunt for a small or slowly moving prey,”, say Dr. Loba and Dr. Radwańska.

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Holotypical lateral plate (MWGUW ZI/72/032) of a new brittle star genus and species Ophiobartia radwanskii gen. et sp. nov., seen under a scanning electron microscope (SEM) from the inside. Credit: Dr. Michał Loba

Dr. Loba and Dr. Radwańska remind that echinoderms are a very ancient group of animals and brittle stars appeared among them in the Palaeozoic. Brittle stars with ‘modern’ anatomy, the one they currently have, appeared in the beginning of the Mesozoic, in Trias (not earlier than approx. 250 million years ago).

Skeletons of fossil brittle stars are sometimes preserved entirely as fossils. These, however, are relatively rare situations. In most cases, the skeleton breaks down after the death of the animal and the decay of soft tissues. Individual skeletal fragments end up in the sediment. In the fossil record you can find basically all types of calcite tiles that build brittle star skeleton during the animal’s lifetime. Lateral tiles have the greatest diagnostic value for palaeontologists. It has been shown that fossil species can be identified based on them.

Scientific publications dealing with isolated tiles of brittle stars have been appearing for a long time in Western Europe, while the area of Poland was very poorly studied in this respect until recently.

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