Trilobites are one of the most common fossils in the world.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/768px-Kolihapeltis_01_Pengo.jpg)
They formed one of the earliest known groups of arthropods, and they can tell us a lot about the way life evolved hundreds of millions of years ago.
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So without further ado, let’s look at some facts of everyone’s favorite fossil.
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They thrived for almost 300 million years, from the Lower Cambrian (521 million years ago) to the start of the Mesozoic (250 million years ago).
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Cheirurus_ingricus_-_trilobite_-_Smithsonian_Museum_of_Natural_History_-_2012-05-17.jpg)
That means their period was hundreds of millions of years earlier than the Jurassic, when dinosaurs ruled the Earth.
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Trilobites are extinct arthropods, and some of the earliest one at that. They are distant relatives of modern lobsters and spiders.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/CyphaspisPlate.jpg)
They lived in marine waters, although only some of them could actually swim.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Elrathia_kingii_growth_series.jpg)
Many burrowed or crawled around on muddyseafloors. They were the first creatures to develop complex eyes.
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Their fossilized remains have been found on every continent on Earth, indicating that they thrived in all regions of the planet and all climates.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Trilobite_Ordovicien_8127.jpg)
This is why they’re some of the most common fossils.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Trilobite_Walliserops_trifurcatus.jpg)
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They could almost certainly roll up into a ball when threatened and some exoskeletons were covered in spines and bumps for added protection (or perhaps reproductive purposes).
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/1911_Britannica-Arachnida-Sao_hirsuta.png)
Also like many modern arthropods, they molted. This means they shed their exoskeleton as they grew.
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They greatly varied in size, from less than 1 cm to over 70 cm.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/SamGonIII_3lobes.png)
They’re called ‘trilobites’ because their body could be split into three parts both longitudinally and axially.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/SamGonIII_cephareas.png)
There are 10 “Orders” of trilobites featuring over 20,000 recognized species.
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Trilobite fossils are so well studied and understood that some species actually serve as a marker for dating geological layers.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/SamGonIII_cranidium.png)
Some trilobite fossils show signs of predation so something definitely ate them.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Triarthrus_NT_small.jpg)
They had many different lifestyles: some moved over the seabed as predators, scavengers, or filter feeders, while others swam and fed on plankton.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Trilobite_cephalon_ventral_anatomy.png)
Some trilobite species may have developed symbiotic relationships with sulfur-eating bacteria from which they derived food.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/trilobite_exoskeleton.jpg)
They survived through several extinction events not really all that surprising, as they were around for almost 300 million years.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Trilobite_facial_suture_types.png)
Still, trilobites maintained a healthy level of diversity all throughout their history before ultimately fading out at the end of the Permian.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Trilobite_hypostome_types_based_on_attachment_labeled.png)
Within the marine paleoenvironment, trilobites were found in a broad range of water depths, from extremely shallow to very deep.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Trilobite-cross-sections.jpg)
Most trilobite fossils are actually the remnants of their shed exoskeletons and not the trilobite themselves.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/15_12_Postikaolishania_jingxiensis.jpg)
Collecting trilobites has a long history. Trilobite fossils have been found in burial grounds dating back more than 50,000 years.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Cambrian_Trilobite_Olenoides_Mt._Stephen-scaled.jpg)
The study of Paleozoic trilobites in the Welsh-English borders by Niles Eldredge was important in establishing the theory of evolution.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Asaphus_expansus_ventral-scaled.jpg)
A trilobite’s cephalon, or head section, shows incredible complexity for the time.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Asaphiscuswheelerii.jpg)
They had a single pair of antennae and otherwise undifferentiated biramous limbs.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Agnostid.jpg)
Lenses of trilobites’ eyes were made of calcite, which is transparent when extremely pure.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Crotalocephalus_Trottier.jpg)
Some species had hundreds of individual lenses in each eye. Despite this, other species were completely blind likely because they lived too deep for light to reach them.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Flatfish_Lhwyd.jpg)
They had a toothless mouth that faced backwards, in front of their legs.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/Joachim_Barrande01.jpg)
We’re not really sure where their heart, brain, and liver were situated.
![](https://worldnewsroom.info/eng/wp-content/uploads/2022/08/P550300_1332x690-960x497-1.jpg)
Trilobites were ultimately wiped out by the largest extinction event in our planet’s history 250 million years ago, when 90% of all species on earth suddenly perished.
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