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Temporal range: Middle Ordovician–Late Ordovician
Isotelus brachycephalus.JPG
Isotelus brachycephalus
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Trilobita
Order: Asaphida
Superfamily: Asaphoidea
Family: Asaphidae
Genus: Isotelus

Isotelus is a genus of asaphid trilobites from the middle and upper Ordovician period, fairly common in the Northeastern United States, northwest Manitoba, southwestern Quebec and southeastern Ontario. One species, Isotelus rex, is currently the world's largest trilobite ever found as a complete fossil.

Discovery and naming[edit]

Cast of Isotelus rex

A specimen of Isotelus rex, from Churchill, Manitoba, is the largest complete trilobite ever found. Discovered by Dave Rudkin (Royal Ontario Museum), Robert Elias (University of Manitoba), Graham Young (Manitoba Museum) and Edward Dobrzanske (Manitoba Museum) in 1999, it measures 720 millimetres (28 in) in length, 400 millimetres (16 in) in maximum width (across the cephalon) and 70 millimetres (3 in) in maximum height (at the posterior midpoint of the cephalon).[1][2][3]

Many specimens have also been found in Ohio, where Isotelus maximus is the state fossil.[citation needed] [4]


  • Very similar to Homotelus
  • “Double” posterior
  • Head and tail shields are semi-circular and very similar in shape (isopygus)
  • Thorax has 8 segments and a slightly raised middle lobe between the outer pleurae


External links[edit]