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Man is a social animal, it is said. But how long have animals been social? A study published Thursday, October 17 in the journal Scientific Reports reports the discovery of what could have been the oldest collective behavior ever observed. It goes back to 480 million years ago.
Trilobites are ancient animals. " These are arthropods, which existed during the first period of the history of life, the Paleozoic, " says Muriel Vidal, CNRS professor-researcher at the University of Brittany , who participated in this research. These animals are well known, and they are very similar to woodlice " but live in marine environments, such as Norway lobster today ".
Fossils discovered in Morocco
Many fossils have been discovered, but those found in the massif of Fezouata in Morocco are particular. It is about several specimens, " almost nested one after the other, perfectly aligned ", remembers Muriel Vidal. This particular disposition is intriguing to paleontologists, especially as the geological conditions of the excavation site make it possible to explain the fossilization conditions of this trilobite colony relatively well. " They were probably fossilized while they all made the same movement, it's a snapshot of life, " says the researcher. " It made us think of what we can find in nature today. American lobster, for example, has the same behavior with individuals in single file that can be observed during migration. "
Migration behaviors
These fossil arrangements would therefore be the trace of a similar migration behavior. This hypothesis is also supported by the analysis of the terrain around it. Its layout makes it possible to deduce that these animals were at the level of " the limit of action of the storm waves on the bottom, " says Muriel Vidal. Depending on the time of the year, depending on the depth of the water, trilobites could be affected by waves caused by strong winds on the surface. " This makes sense of a migration hypothesis related to storms, " says the teacher-researcher.
But were such weather phenomena quite common at the time? Probably: 480 million years ago, according to the tectonic movements, Morocco was near the South Pole. The climate also favors this hypothesis, since there followed then warm and cold periods, " glacial and interglacial, " explains Muriel Vidal. " As all this is happening near the South Pole, we have some very interesting things to identify. "
If these trilobites have actually migrated to cope with polar storms, then this would be the first observed collective animal behavior. A social bond, almost half a billion years old.