Six periods and a slow goodbye
From the Cambrian explosion to the edge of the Great Dying.
How this site works. Every fact is in our own words and linked to its source, beside it. Where good sources disagree, we show each version in a “Sources differ” box.
When they lived
Trilobites appeared in the Cambrian Period, 538 to 485 million years ago. NHM
When did the first trilobites appear? Sources differ
- The first are known from around 520 million years ago. NHM
- Britannica puts their first appearance at 521 million years ago. Britannica
That makes them about 100 million years older than the first shark and 290 million years older than the first dinosaur. NHM
They lasted more than 250 million years, through six geological periods. NHM
An NHM news story says their fossil record spans 275 million years. NHM news
Our own species has been around for only 0.1% as long as trilobites lasted. NHM
Where did they come from?
They appear suddenly in Cambrian rocks, and how they evolved is still a mystery. NHM
Is Spriggina related? Sources differ
- Spriggina, a segmented animal from 550-million-year-old rocks in Australia, looks a bit like a trilobite, but scientists now think the two are unlikely to be related. NHM
- Britannica says Spriggina may be an ancestor of the trilobites and other arthropods. Britannica
A tool for geologists
Because there were so many and new species evolved fast, they are excellent index fossils for dating rocks. NHM
Paradoxides is found in England, Wales, Newfoundland, Sweden, Spain and Siberia, showing those rocks are all middle Cambrian. BGS
Different trilobites on each side help show that Scotland was once near North America, across an ocean called Iapetus. BGS
In Britain, trilobites are found in Cambrian, Ordovician and Silurian rocks in Wales and the Welsh Borderland, in Devonian rocks of south-west England and in Carboniferous rocks in places such as Lancashire. BGS
A long decline
Extinctions at the end of the Cambrian wiped out many early groups. NHM
An ice age at the end of the Ordovician, 440 million years ago, hit them again. NHM
The survivors bounced back in the Silurian, splitting into as many species as before. NHM
At the end of the Devonian, oxygen-poor water killed off coral reefs, an important trilobite home. NHM
After that only one group, the Proetida, continued into the Carboniferous and Permian. NHM
When did the last trilobites die out? Sources differ
- They vanish from the fossil record just before the Great Dying at the end of the Permian, when 90% of animals were wiped out. NHM
- The British Geological Survey says they finally died out at the end of the Permian, about 250 million years ago. BGS
- The UC Museum of Paleontology says the last went extinct about 245 million years ago. UCMP Berkeley
None survive: there is no sign of hidden living trilobites in the deep ocean. NHM
Chitons, woodlice and sea isopods look a bit like trilobites, but none is closely related. NHM
How close are horseshoe crabs? Sources differ
Next: the Dudley Bug →