The trilobite, a marine animal that is a symbol of paleontology, is an amazing creature that survived two mass extinctions and dominated the ancient seafloor for 300 million years.
How could trilobites survive for so long in a time when the Earth's oxygen levels were so turbulent that they could change at any time?
According to Spanish and American paleontologists, the clue lies in a variant of the trilobite, Aulacopleura koninckii.
According to them, this trilobite was able to survive harsh environmental changes because it was able to cope with low oxygen levels by increasing the number of body segments.
A Strange Species of Trilobite with Different Number of Body Segments in Different Individuals
During the period of about 300 million years, from the Cambrian period (about 520 million years ago) to the end of the Permian period, the ancient oceans were teeming with trilobites.
This symbol of paleontology has lived on Earth much longer than dinosaurs, surviving even two mass extinctions.
More than 20,000 species of trilobites are known, but their bodies have the same basic structure, divided into three parts: head, thorax, and tail plate. Most species also have a fixed number of body segments.
Aulacopleura koninckii, however, is somewhat unique. It is unusual in that it has a third eye, but it is also unique in that the number of body segments varies from 18 to 22, depending on the individual.
To realize the wonder of this, consider this.
Humans have a fixed number of backbones, 24. This is "basically" the same for all people, no matter how short or tall they are. However, in Aulacopreura, the number varies from one individual to another.
The question is why. Is there any advantage to having more body segments?
A team of paleontologists from the Universidad Complutense de Madrid and the University of California, Riverside, is trying to answer that question.
Why can't more body segments be rounded to protect themselves?
Modern-day sowbugs try to protect themselves by curling their bodies into a ball-like shape when exposed to danger. They keep their hard shells on the outside so that their weak point, their bellies, are not visible to their enemies.
Trilobites can also defend themselves in the same way. In this ball-like posture, the tail snaps under the head to hide the soft parts.
However, the 3D model created this time shows that in the case of Aulacopreura, the tail plate is too long to fit under the head, thanks to the increased body segments.
The GIF below shows a young trilobite with the common body segments so that the underside of the head and tail plate fit snugly together when in a defensive posture. But this is not the case in Aulacopreura. Their tails stick out and they are unable to curl up completely.
The Aulacopreura survived its harsh environment by increasing its body segments to allow for easier respiration.
If this is the case, why would they increase their body segments at such a risk?
What is noteworthy here is the "legs" that lie beneath the body segments. In fact, trilobite legs serve as gills. In other words, they are part of the respiratory apparatus.
Therefore, the more body segments they have, the easier it is for them to breathe.
Based on this, the research team believes that Aulacopreura may have been able to survive on the seafloor, where oxygen is scarce, by increasing the number of body segments.
Dangerous predators cannot approach such an oxygen-poor environment. However, Aulacopreura may have been able to live there without running out of oxygen because of its extra gills.
The trilobites may be teaching us that flexibility and the ability to adapt to the environment are necessary for survival in the harshest environments on earth.
References:Scientists discover how trilobites survived environmental change
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