Washington, May 9 (ANI): The discovery of giant trilobites in northern Portugal reveals the once ubiquitous marine creature mated in groups and used its numbers for protection.
Trilobites once roamed the sea floor, but were wiped out in the Permian-Triassic extinction, 250 million years ago.
These marine arthropods, typically less than 8 centimeters long, are distant relatives of modern-day lobsters and spiders.
But, the new find describes giants that grew to 90 centimeters in length, the largest ever found.
Researchers, led by Dr Juan Carlos Gutierrez-Marco from the El Instituto de Geologia Economica in Madrid, Spain, discovered trilobites from 15 genera in 465-million year old rocks in Arouca Geopark in northern Portugal.
They found a complete specimen 70 centimeters in length and others whose tail remnants indicated they grew to up to 90 centimeters long.
Most of the trilobite species they collected have been found elsewhere in Western Europe, but never before of such giant size.
Their size was probably an adaption to the polar waters where they dwelt, according to the researchers.
"Metabolism of invertebrates is slower in cold water, so it takes longer to reach adulthood and they also tend to live longer. Also, if you are bigger you are better able to deter a predator attack," said co-author Dr Diego Garcia-Bellido, also of the El Instituto de Geologia Economica.
The researchers found clusters of trilobites with up to 1000 individuals, indicating they grouped together to molt, much like modern-day horseshoe crabs.
The researchers assume that like horseshoe crabs, the trilobites may have also mated en masse.
"The hormones that instigate molting are related to those that induce sexual reproduction," said Garcia-Bellido.
Several trilobites in the deposit were also found in burrows and under the shells of larger organisms, where they may have hidden after molting as their soft bodies made them more vulnerable to predators.
The trilobites are believed to have died when the stagnant seawater became oxygen-depleted, which also helped their preservation as fossils, the researchers said.
Palaeontologist Dr John Paterson from the University of New England in Armidale, describes the find as "spectacular".
"It's really exceptional in that you rarely find trilobite fossils complete," he said. "Mostly you find a piece of the head or the tail, so to find them in congregations where there are many complete individuals is astounding," he added. (ANI)