Where the facts come from
Every factual claim on this site links to its source. This is the full list.
How we checked
Each fact was written in our own words alongside its source. Our build script stores the text of every source and, for each fact, checks that the key words and figures really appear in it. 136 of 136 checks passed when this site was last built (13 November 2026). Where we couldn’t find a named source saying something, we left it out. Where good sources disagree, we say so and give both.
Where sources differ
- What the name refers to. The NHM explains ‘three lobes’ and describes both the head-to-tail and side-to-side splits; the British Geological Survey says the name refers to the side-to-side split only.
- When they first appeared. About 520 million years ago (NHM) or 521 million years ago (Britannica).
- How long they lasted. More than 250 million years (NHM feature) or a fossil record spanning 275 million years (NHM news story).
- When they died out. Just before the end-Permian Great Dying (NHM), at the end of the Permian about 250 million years ago (BGS), or about 245 million years ago (UC Museum of Paleontology).
- Spriggina. Possibly ancestral to trilobites (Britannica) or unlikely to be related (NHM).
- What they ate. Predators, scavengers, mud-grazers, filter feeders and plankton-eaters (NHM, Britannica); Dudley Council’s page says they probably grazed on plants.
- Horseshoe crabs. Perhaps the closest living relatives (NHM feature), and only distantly related (NHM news story).
- The age of Wren’s Nest. 427.7 to 429 million years (Black Country Geopark), about 420 million years (Dudley Council), 428 million years for the Ripple Beds (Dudley Council), or about 430 million years (Scientific American blog).
- The size of Wren’s Nest. About 101 acres, 45 hectares (Geopark), or 100 acres (Dudley Council).
- The biggest trilobite’s name. The NHM page spells it “Isoteus rex”; the usual spelling is Isotelus rex.
All sources (9)
- Natural History Museum: How trilobites conquered prehistoric oceans (64 facts)
- British Geological Survey: Trilobites (28 facts)
- Dudley Council: Geology of Wren’s Nest National Nature Reserve (12 facts)
- Black Country Global Geopark: Wren’s Nest National Nature Reserve (8 facts)
- Encyclopaedia Britannica: Trilobite (8 facts)
- Natural History Museum news: Trilobite fossil reveals how ancient arthropods mated (2022) (7 facts)
- Scientific American blog: The Dudley Bug (Glendon Mellow, 2011) (4 facts)
- UC Museum of Paleontology, Berkeley: Introduction to the Trilobita (3 facts)
- Dudley Council: Wren’s Nest National Nature Reserve (2 facts)