Isotelus maximus

I maximus 250px

Phylum: Arthropoda
Class: Trilobita
Order: Asaphida
Family: Asaphidae
Genus: Isotelus
Species: Isotelus maximus (Locke, 1838)

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Stratigraphic Occurrences

I. maximus_strat

Geographic Occurrences

Map point data provided by iDigBio.
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Sequences (Formations)

  • C6 Sequence (Elkhorn)
  • C5 Sequence (Whitewater, Liberty, Waynvesville)
  • C4 Sequence (Arnheim)
  • C3 Sequence (Mount Auburn, Corryville)
  • C2 Sequence (Bellevue, Fairview: Fairmount, Mount Hope)
  • C1 Sequence (Clays Ferry/Kope: McMicken, Southgate, Economy/Fulton)

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Identification in Hand Sample

  • characteristic geneal spines extend as far back as the fifth or sixth segment.
  • May obtain up to 50cm in length.
  • Pygidium large, short and rounded.
  • Cephalon also large and rounded.
  • Isotelus is the State Invertebrate Fossil of Ohio and one of the largest known trilobites!
  • Articulated (full specimens) of Isotelus are very rare, instead cranidial fragments, pygidial fragments, and thoracic segments are the most common.

Isotelus maximus from Liberty Formation of Preble County, Ohio (MUGM 28978)

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Davis (1998):

  • Large pygidium matches cephalon in size and shape. Largest specimens exceed 0.6m (2 feet) in length, entire Cincinnatian.

McFarlan (1931):

  • This species has commonly been distinguished from the preceding by the development of genal spines extending back as far as the fifth or sixth thoracic segment. According to Raymond and Narraway (1910, p. 55), the pygidium is short and rounded, contrasting with the subtriangular form of I. gigas. In this, it agrees with the young individuals of that species. It does not attain the large size of I. gigas.

Cummings (1907):

  • Locke’s specimen has a “kind of shovel-shaped termination at both ends…large eyes, placed on the highest part of his body… The animals were of various sizes, from less than an inch in length to 21 inches “” ‘It [the specimen] is a fragment of the under margin of the tail or post abdomen of the animal, and when viewed sideways, exhibits a convex and a concave part precisely like the ‘moulding’ called the “O-gee”” … I am not sure that my specimen is not actually an overgrown megalops of Green; the character ‘cauda suborbiculari limbo lato.’ applies exactly, and the only definable difference which I can perceive between Dr. Green’s specimen and my own is that the length of the post abdomen in his specimen is two-thirds of its width, while in mine it is less than two-thirds. The size, which is hardly a character, is very different, his being 5 inches, and mine 21 inches in length. I merely propose it as a new species, under the name of maximus, leaving it for those who have the means of more extensive comparisons than I possess to determine the question. (Locke, 1838)”

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