Trilobites fossils are any arthropod that has three lobes and three segments, making it easy to identify as a representative of this genus of prehistoric fossil arthropods. Trilobites, which are only aquatic creatures, originally emerged somewhere at the start of the Cambrian Period, or roughly 542 million years ago, when they inhabited the oceans.

Trilobites were some of the earliest organisms to flourish, living in the seas for about 270 million years and having over 22,000 distinct species identified. Due to their sheer numbers, and preservation, they are among the best-studied extinct species.

Featured Image Credit: Kevin Walsh


Similar to other arthropods, Trilobites featured an exoskeleton that was made of calcified substances. The exoskeleton was necessary to abandon for the species to mature, and lost Trilobite exoskeletons, or parts of them, are rather commonplace fossils. Each Trilobite body part was equipped with a set of fused appendages. The appendages closest to the head were transformed into sensing and nourishment functions.

Trilobites were ancient marine arthropods with distinctive three-lobed body and intricate exoskeleton
Trilobites were ancient marine arthropods with distinctive three-lobed body and intricate exoskeleton

Credit: Kevin Walsh

A set of compound eyes were present in the majority of Trilobites, but others were visually impaired. Three anatomical segments were made up of Trilobites, 2 of which were located on either side of a longitudinal axial lobe. Spanning head to tail, the Trilobite’s body was divided into three segments, with the cephalon, or head area, being segregated from the thorax.


Like its big and crustacean relatives, Trilobites possessed openings on the lowered section of their heads and a variety of intricate mouth appendages to aid in feeding.

Trilobites developed into a variety of ecosystems; several paddled and consumed phytoplankton, while others roamed across the seafloor as carnivores, scavengers, or filter feeders. Some might even wriggle onto the ground. Evidence suggests that they even managed to reach land. All in all, due to its vast diversified species, experts cannot pinpoint to actual direct prey that Trilobites would consume.


Trilobites are invariably discovered in strata that also include the petrified remnants of other salt-water species like brachiopods, and corals, suggesting that they were predominantly marine species. Trilobites may have made a few brief forays onto land, according to various trackways.

Trilobites thrived in a variety of habitats including shallow and deep seas, reefs, and even freshwater environments
Trilobites thrived in a variety of habitats including shallow and deep seas, reefs, and even freshwater environments

Credit: Lex McKee

Trilobites were discovered in a wide variety of marine environments, from really shallow to extreme water depths. Trilobites, like its contemporary, are present on every present continent and confirmed to have existed in every Paleozoic sea, out of which remains have been recovered.


In times of molting the exoskeleton, Trilobites would form clusters that would also serve as mating grounds. Trilobite males would seek out female counterparts to mate, with special appendages dedicated to the process termed “claspers mating strategy” that prevails today in a few similar species. The male would presumably climb on top of the female before courting, aligning his head with the female’s backbone. Several spines that extend from the tail are present at this location on the exoskeleton. The claspers allowed the male to grab onto the two pairs of the female’s spines since this would align their bodies perfectly.


To prevent predation, many Trilobites had protective spikes and thorns on their bodies. Certain Trilobite species would roll into a ball that was immune to biting or a predator’s keen teeth by using their impenetrable exoskeleton. Some species of Trilobite developed camouflage to hide from predators, as noted from trilobite fossils.

Great example of recreated Trilobites noted for their compounded eyes
A great example of recreated Trilobites noted for their compounded eyes

Credit: Ángel M. Felicísimo

Even though they were common in many environments, they became extinct approximately 200 million years ago. A mixture of reasons is probably to blame for the recurrent extinction episodes usually succeeded by false recoveries that can be found all through the Trilobite archaeological record.

Facts about the Trilobite

  1. There are 20,000 confirmed Trilobite species.
  2. Most Trilobite fossils are abandoned exoskeletons.
  3. Trilobite fossils have been used by Native Americans for amulets.
  4. Trilobites were first available 542 million years ago.
  5. Trilobites went extinct around 252 million years ago.


What is the closest living creature to Trilobites?

Isopods might be the group that comes closest to drawing off a convincing Trilobite mimic. After all, they are both members of the Arthropoda phylum, which includes organisms with hardened, segmented shells and many legs.

How did Trilobites survive for so long?

Trilobites were highly adaptable species, thanks to their numerous mating strategy and defensive countermeasures, which allowed them to thrive all over the world. In 300 million years of activity, they managed to survive quite a few mass extinction events before finally fading from existence in the event that wiped out 90% of species roaming the planet.

How big were Trilobites?

Trilobite size ranged between 1.2–3.9 inches, with sizes ranging from extremely small, less than an inch, to very enormous, 12 inches. Isotelus rex, the world’s largest known Trilobite fossil specimen, measures 28 inches in length. Just on the beaches of Hudson Bay, in Ordovician strata, it was discovered in 1998 by Canadian researchers.

Did Trilobites have eyes?

The earliest truly complex optics were found in Trilobites. They had compound eyes, with numerous distinct ommatidia groupings of photoreceptor cells, each having its own focus, which further combines all of the input into a mosaic-like image in the species’ brain.

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