Fossil

Tullimonstrum gregarium

Tully monster

Tullimonstrum gregarium, the Tully monster, is the Mazon Creek soft-bodied animal with a long proboscis ending in a toothed claw, eyes on stalks and a torpedo body, and the state fossil of Illinois; its affinities swing between vertebrate and invertebrate with each new paper. Specimens are found only in Mazon Creek ironstone concretions, mostly from Pit 11 in the strip-mining era, and good ones are expensive. Faint or partial Tully monsters are frequently over-interpreted, so buy from dealers who show both halves.

Group	Fossil
Rank (PBDB)	genus· Paleobiology Database
Author	Richardson 1966· Paleobiology Database
Classification (PBDB)	Chordata › Petromyzontida › NO_ORDER_SPECIFIED › NO_FAMILY_SPECIFIED· Paleobiology Database
Range (PBDB)	313–306 Ma· Paleobiology Database
PBDB occurrences	3· Paleobiology Database

Photographs

Tullimonstrum gregarium — Tullimonstrum gregarium Richardson, 1966, NON-TYPE (NHMUK PI A 11132 a) — Tullimonstrum gregarium Richardson, 1966, NON-TYPE (NHMUK PI A 11132 a) — © The Trustees of the Natural History Museum, London, Natural History Museum (London) Data Portal, CC BY 4.0

Tullimonstrum gregarium — Tullimonstrum gregarium Richardson, 1966, NON-TYPE (NHMUK PI A 10459 b) — Tullimonstrum gregarium Richardson, 1966, NON-TYPE (NHMUK PI A 10459 b) — © The Trustees of the Natural History Museum, London, Natural History Museum (London) Data Portal, CC BY 4.0

Tullimonstrum gregarium — Tullimonstrum gregarium Richardson, 1966, NON-TYPE (NHMUK PI A 11131 b) — Tullimonstrum gregarium Richardson, 1966, NON-TYPE (NHMUK PI A 11131 b) — © The Trustees of the Natural History Museum, London, Natural History Museum (London) Data Portal, CC BY 4.0

Elsewhere

Cite this article

Stratum Study. "Tullimonstrum gregarium" (Taxon). Stratum Study pack 2026.09, as of 2026-09-19. https://stratum.black/study/taxa/tullimonstrum-gregarium. Accessed 2026-09-20.

BibTeX · CSL-JSON

@misc{stratum-tullimonstrum-gregarium,
  title        = {Tullimonstrum gregarium},
  author       = {{Stratum Study}},
  howpublished = {\url{https://stratum.black/study/taxa/tullimonstrum-gregarium}},
  year         = {2026},
  note         = {Taxon article, Stratum Study pack 2026.09, as of 2026-09-19; sources: stratum, pbdb, wikidata, commons, nhm. Accessed 2026-09-20.}
}

Citations carry the pack version and the article's as-of date so they resolve to the same text later. The facts themselves belong to the sources listed below; cite those for the science.

Photographs

Age

Formations

Elsewhere