Trilobites: Creatures That Lived 252 Million Years Ago

A trilobite fossil.

Our knowledge about trilobites comes from fossils. (Image: GNU FDL via Wikimedia Commons)

Trilobites refer to a group of marine artiopodan arthropods that are now extinct. In fact, they are known as the earliest arthropod groups, having existed even during the Early Cambrian period 521 million years back. At the end of the Permian period around 252 million years ago, trilobites are believed to have undergone mass extinction.


Since trilobites are now extinct, much of our knowledge about these creatures comes from fossils. Such fossils are typically impressions of their shells in sediment which eventually become hardened rocks. trilobites had a soft body that was protected by an exoskeleton. Normally, only the dorsal parts of the exoskeleton that covered the back portion of trilobites were fossilized. The ventral parts, which refer to the underside, are not fossilized probably because they were covered by a soft membrane.

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The exoskeleton is divided into three sections — thorax, cephalon (head shield), and pygidium (tail shield). Some types of trilobites are known to have had eyes while others were blind. The eyes were situated at the inner edge of the free check. trilobites’ eyes were usually compound eyes, meaning that they consisted of several separate lenses, the number, and complexity of the eye structure varying enormously.

Some trilobites had large, convex compound eyes that gave them a very wide field of view. On the contrary, some types had smaller eyes due to which they had a restricted view. The surface of the exoskeleton also had organs like canals, pits, spines, tubercles, and so on. These creatures had multiple pairs of limbs — three beneath the cephalon and one under each segment of the thorax and pygidium.

A trilobite.
A trilobite’s exoskeleton is divided into three sections. (Image: via Wikimedia Commons)

Different trilobites lived at varying depths in the seas. As such, their fossils can be used as indicators of the palaeoenvironment, which refers to an environment at a period in the geological past. For instance, a genus named Whittardolithus is believed to have lived in deep-sea bottoms while another genus called Neseuretus lived in areas that were shallow-water deposits.

The varying body sizes and shapes also indicate that trilobites lived in a wide range of ecosystems. They were probably blind and likely lived deep within the sea, possibly on the sea floor where light is limited and even non-existent. Some trilobites like Cyclopyge had large eyes that allowed them to see in all directions, which is probably an indication that these creatures lived above the seafloor.

Interesting facts

Trilobites can be found on every single continent. More than 20,000 species have been identified, with some of the biggest ones extending up to 28 inches long, while the smallest one is less than a millimeter in length. Some of them had smooth, rounded shells covering them while others had defensive spines all across the body. When under attack or in danger, some of these creatures rolled up into balls.

Over 20,000 species of Trilobites have been identified.
Over 20,000 species of trilobites have been identified. (Image: via Wikimedia Commons)

During the course of its life, a trilobite would have numerous exoskeletons that it used to grow and discard. It is these discarded exoskeleton husks that make up the bulk of the fossils and not the actual creature. Fossils of actual trilobites are very rare.

Trilobites died in an era that is often called the “Great Dying” age, which was around 250 million years ago. During this time, almost 90 percent of the species existing on Earth became extinct, including trilobites. As to why such a mass extinction occurred, theories of volcanic eruptions are popularly cited.

An anomaly

A trilobite fossil was discovered in 1868 by William Meister when he was searching near Antelope Springs, Utah. The interesting thing was that the fossil was crushed under what seems to be human footprints, and that too, of someone wearing shoes or sandals with distinct heel marks. Keep in mind the age of the fossil (500 million years). This fossil was used to debunk the evolutionary theory. The scientific community, however, attributed the fossil to “natural” formations. 

“No intellectually honest individual examining this specimen can reasonably deny its genuine appearance,” declared Melvin Cook, a believer of Creationism, who wrote an article, Why Not Creationism? regarding the footprint in 1970. Scientists believe that humans came into the world around 1-2 million years ago, while wearing shoes hasn’t been popular for more than 1,000 years at most.

Another fossil discovery was made by Dr. Clifford Burdick in 1968 in Antelope Springs, Arizona. It was apparently made by a child’s foot. 

Mr. Meister was offered a reward of US$250,000 for the fossil by a geologist. When asked what the geologist would do to the fossil, he replied that it would be destroyed immediately as the fossil would destroy the geologist’s entire life’s work. Science was meant to enlighten. But given the many examples, it now mostly serves as a tool for disinformation and censorship by those in power. 

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