Phylum: Mollusca
Class: Bivalvia
Order: Pterioida
Family: Ambonychiidae
Genus: Anomalodonta Miller, 1874
Cincinnatian Species: Anomalodonta gigantea

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Geologic Range
Late Ordovician

Common Paleoecology
Anomalodonta is an extinct genus of stationary epifaunal suspension feeders

Identification in Hand Sample:

  • Broad, radial plications
  • Lacks lateral teeth, and has only a single poorly developed cardinal tooth, or no cardinal tooth at all
  • Adductor muscular impressions on the anterior side
  • Strong posterior alation

Geographic Occurrences

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Fossils of Ohio (1996):

  • Radial ornamentation is broad plications
  • The Upper Ordovician genus Anomalodonta is represented by A. gigantean Miller, a large species that lacks auricles and has broad, radial plications.

Treatise on Invertebrate Paleontology, Part N, Mollusca 6 (1 of 3) (1969):

  • Large, simplicicostate monomyarian upright ambonychiids similar to Ambonychia; lacking lateral teeth and with only single poorly developed cardinal tooth in RV. (May be synonymous with Ambonychia s.s.)

McFarlan (1931):

  • Distinguished from Byssonychia in the absence of cardinal and lateral teeth. Distinguished from Allonychia in the more oblique form and strong posterior alation.

Miller (1874):

  • Equivalve, inequilateral, byssal sinus on the anterior side, immediately below the beak. Cartilage grooves running from the cardinal tooth beneath the beak to the termination of the wing posteriorly, and varying in number in the same species with the size and age of the shell, and having the same number of cartilage grooves on the anterior side of the cardinal tooth, that run together as they pass into the byssal sinus, immediately below the beak, which vary in number under the same circumstances. Adductor muscular impressions on the anterior side, below the byssal sinus. The other muscular impression probably placed posteriorly on the wing.
  • This genus will include the Ambonychia alata (Meek). “Ohio Pal.,” vol. I, p.131. Mr. James has a specimen of this species , which shows enough of the hinge line to leave no doubt that it is not an Ambonychia , and that it must be placed in this geuns. And it will probably include Megaptera casei (Meek and Worthen) “Ill.Geo.Sur .vol. iii, p.337, and “Ohio Pal.”vol.i.p.132, because the general appearance, and the apparent thickening of the shell on the posterior wing, renders it most likely that it does not possess the internal markings of the genus Ambonychia, and quite possible that it does not have the hinge line of this genus. The Anomalodonta alata and Megaptera casei are both found in the upper part of the Cincinnati group, in strata about the equivalent of the Versailles rocks, where Anomalodonta gigantean is found. The Megatera casei being found at Richmond, Indiana, and the Anomalodonta alata in the vicinity of Morrow, Ohio.
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A. gigantea