Stratum.black
Placenticeras meeki — Placenticeras meeki
Placenticeras meeki — Hectonichus, Wikimedia Commons, CC BY SA 3.0

Ammonoid

Placenticeras meeki

Ammonite

Placenticeras is the large, smooth, discoidal ammonite of the Pierre Shale and Bearpaw Formation, the genus that produces iridescent ammolite in Alberta and the red-green nacreous ammonites of South Dakota. Complete P. meeki with shell are prized; steinkerns with exposed sutures are cheaper and also collectible. Look for repaired body chambers and shell reattached over fill.

PhylumMollusca
ClassCephalopoda
OrderAmmonitida
FamilyPlacenticeratidae
GroupAmmonoid
Sizeto 60 cm
Rank (PBDB)genus· Paleobiology Database
AuthorMeek 1876· Paleobiology Database
Classification (PBDB)Mollusca › Cephalopoda › Ammonitida › Placenticeratidae· Paleobiology Database
Range (PBDB)106–66 Ma· Paleobiology Database
PBDB occurrences241· Paleobiology Database

Restoration and fakes

Large Pierre Shale ammonites are commonly assembled from concretion fragments and gap-filled; shell may be stabilised with resin that mimics nacre.

Photographs

Placenticeras meeki — Placenticeras Meek, 1876 (NHMUK PI CA 5576)
Placenticeras Meek, 1876 (NHMUK PI CA 5576) — © The Trustees of the Natural History Museum, London, Natural History Museum (London) Data Portal, CC BY 4.0
Placenticeras meeki — Placenticeras Meek, 1876 (NHMUK PI CA 5577)
Placenticeras Meek, 1876 (NHMUK PI CA 5577) — © The Trustees of the Natural History Museum, London, Natural History Museum (London) Data Portal, CC BY 4.0

Age

Formations

Elsewhere

Cite this article

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

BibTeX · CSL-JSON

@misc{stratum-placenticeras-meeki,
  title        = {Placenticeras meeki},
  author       = {{Stratum Study}},
  howpublished = {\url{https://stratum.black/study/taxa/placenticeras-meeki}},
  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.}
}

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