Of the incredible creatures that once dominated the Earth, it is the larger, terrestrial animals that get the most attention. From dinosaurs to giant spider fossils discovered in Australia, and even a giant "car-size" prehistoric insect fossil that solved an evolutionary mystery, these animals are fascinating to the masses.
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Just as fascinating, however, are the prehistoric animals that lived in the oceans millions to billions of years ago. While the largest marine reptile in history being found has gotten attention as of late, it is the smaller creatures that carry more mysteries, such as when and why a creature that looks straight out of the Alien movies went extinct.
Hundreds of millions of years ago as life on Earth was beginning, trilobites began to appear in oceans worldwide. They lived and thrived during many geological periods before completely going extinct. But what is most interesting about trilobites is how well their fossils have been preserved, which has allowed scientists to learn about life well before the dinosaurs existed and what caused the eventual demise of the trilobites.
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When And Why Trilobites, That Look Straight Out Of Alien Movies, Went Extinct
Trilobites were alien-looking creatures that were abundant in the seas before massive volcanic ash led to their demise
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Trilobites are one of the most successful species that ever lived in the oceans. While it is unclear how they evolved to exist, during the Precambrian Period, trilobites lived in the oceans.
The trilobites were such a well-adapted species that they were able to survive several geological time periods. Those time periods include:
Geological Time Period
Years Of Geological Time Period
Precambrian Period
4.6 billion to 538.8 million years ago
Cambrian Period
538.8 to 485.4 million years ago
Ordovician Period
485.4 to 443.8 million years ago
Silurian Period
443.8 to 419.2 million years ago
Devonian Period
419.2 to 358.9 million years ago
Carboniferous Period
358.9 to 298.9 million years ago
Permian Period
298.9 to 252.2 million years ago
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While the trilobites were able to exist through all of these geological time periods, they eventually ceased to exist. The ancestors of trilobites were first dated to exist 550 million years ago. Their evolution into 22,000 different subspecies of trilobites from these first creatures is remarkable.
It was as the trilobites evolved that they began to take on the appearance of creatures that science fiction films are known for.
However, even the trilobites' evolution could not help the trilobites escape the Permian Period, where there was a mass extinction of animals on Earth.
During the Permian Period, there was massive global warming. Volcano eruptions were common and spewed huge amounts of carbon dioxide into the air. This, coupled with the ash raining down on the oceans, made it difficult for trilobites to survive.
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As the ash hit the water, it covered and "entombed" the trilobites. While this made it so that trilobites are some of the most perfectly preserved fossils today, it also killed the creatures within a matter of hours to days of the ash hitting the water.
This preservation is what has allowed scientists to learn so much about this species that lived for millions of years. Had the hot ash not cooled and mineralized in the oceans, the trilobites would have been instantly turned to ash themselves. But even with all that has been learned about the trilobites in the centuries since they were first discovered during the 1600s, there are still many questions left unanswered.
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What Trilobites Were
Trilobites were marine arthropods that eventually evolved into 22,000 different subspecies
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Trilobites are extinct marine arthropods. While there were many different varieties of trilobites during their existence, what all the trilobites share in common is their bodies were segmented. Some of the trilobites' bodies showed off the three sections perfectly, while others camouflaged their sections.
The three main sections of the trilobites bodies include:
Cephalon
Head
Thorax
Body
Pygidium
Tail
While the trilobites all shared body types, they varied as far as where they lived. This is because while some trilobites enjoyed living on the sea floor, others swam through the oceans looking for food.
Where Trilobites Lived
The different regions of the sea that the trilobites lived in, according to Animals Network, include:
Deep ocean Shallow seas Intertidal zones Ocean floor Swimming through the seas
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Just where and how trilobites lived was all based on how they evolved over time. Those who lived on the ocean floor were blind, while others who swam through the seas had eyesight that was second to none. Because of this, subspecies of trilobite had different prey from one another as well.
Descendants Of Trilobites
Today, there are not any direct descendants of trilobites. Given the appearance of some of the trilobites looking like horseshoe crabs, some believed they were related. There is no relation between trilobites and horseshoe crabs, however.
The closest species to trilobites today include:
Shrimp Sea spiders Scorpions Mites
These living creatures may share similarities, but they are not related at all to trilobites. When trilobites went extinct, their group ceased to exist.
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Trilobites Decline Happened Over Millions Of Years
The extinction of trilobites began in geological time periods before the Permian Period
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Unlike dinosaurs, who went through one mass extinction event, the trilobites slowly became extinct during every geological period they lived through. Therefore, it was not just one moment in time that caused the once varied and populous trilobites to cease to exist. It appears a lack of evolution may be to blame instead.
Well before Earth's last mass extinction, trilobites were already extinct. Given that they had lived for 270 million years successfully, the fact that at the end of the Permian Period they were gone seems unthinkable. But it was before the Permian Period that damage had already been done and the demise of the trilobites was written on the wall.
Despite there being a great many different trilobites over the millions of years they existed, they eventually began to slow their evolutionary process. Many believe that this lack of evolution during the last few geological time periods contributed to their eventual extinction.
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During the Carboniferous and Permian periods, there was only one group from the original 22,000 subspecies of trilobites that survived. The Proetida were smaller in numbers and were believed to be more susceptible to climate change than other trilobites had been.
The Permian Period is known as one of the periods of mass extinction, given that 90% of the animals on Earth died during this time. But the Proetida died before this mass extinction occurred. Being located in shallow seas suggests that the Proetida were looking for warmer waters to survive in. But until more information is known about this subspecies, there will continue to be more questions than answers about Proetida and trilobites in general, and what caused this once mighty group to go extinct.
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