New research by paleontologists from the University of California, Riverside and the Universidad Complutense de Madrid focuses on Aulacopleura koninckii, an unusual species of trilobite that lived around 429 million years ago (Silurian period).
Trilobites are extinct arthropods that dominated the faunas of the oceans of the Paleozoic era.
During their time on Earth, which lasted much longer than the dinosaurs, they survived two major episodes of mass extinctions and dominated ocean floor ecosystems.
Their armored bodies are divided into three sections: a head, a thorax or middle section, and a rigid tail.
There are more than 20,000 known trilobite species and, when mature, most of them have a very specific number of segments in their mid-sections.
However, in Aulacopleura koninckii, paleontologists discovered something unusual.
Though each early growth stage showed little variation in size and shape, mature Aulacopleura koninckii developed anywhere between 18 and 22 mid-section segments.
“We thought this species was weird. We couldn’t understand why Aulacopleura koninckii bodies varied and others living at the same time had a constant number,” said University of California, Riverside researcher Nigel Hughes.
“Seeing trilobites with variable numbers of segments in the thorax is like seeing humans born with different numbers of vertebrae in their backs.”
Like modern pillbugs, trilobites curled up into a ball shape to protect themselves from large squid-like creatures, fish, and other predators.
When rolled up, they could tuck their tails neatly under their heads, so the soft tissues were protected by their hard exterior skeletons.
In the case of Aulacopleura koninckii, 3D modeling showed that protection during rolling up was restricted to smaller, immature forms with less than 18 segments in the middle.
“As the number of segments increased, the body proportions did not allow them to tuck their posteriors neatly under their heads and still be…
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