Phylum: Mollusca
Class: Bivalvia
Order: Modiomorphida
Family: Modiomorphidae
Genus: Modiolodon Ulrich, 1894

Stratigraphic Occurrences


Geologic Range
Middle Ordovician – Upper Ordovician

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

Identification in Hand Sample:

  • 1 to 3 oblique cardinal teeth in each valve
  • Could have horizontal or radial teeth

Geographic Occurrences

Modiolodon from the Whitewater Formation of Clarksville, Ohio (OUIP 2141)

Species Differentiation

Published Description

Pojeta, Jr. & Runnegar (1985):

  • The lateral shape of Fordilla is readily compared with that of various Ordovician modiomorphid isofilibranchs such as Modiolodon, Corallidomus, and Modiolopsis.
  • Modiomorphidae (Modiolopsidae) either lack teeth as in Modiolopsis or have small cardinal teeth on a hinge plate, as in Modiolodon.

Pojeta, Jr. (1971):

  • Based on shell shape and general hard-part morphology such Ordovician modiomorphids as Modiolopsis, Modiolodon, Whiteavesia, and less well-known genera such as Pholadomorpha are strongly reminiscent of the geologically younger modioliform mytilaceans.

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

  • Similar to Modiolopsis, but with 1 to 3 oblique cardinal teeth in each valve

Williams (1916):

  • Two other genera in main characters like Modiomorpha differ from Modiolopsis in the presence of strongly developed cardinal teeth. Curiously enough, both of these genera were founded in the same year and were given the same name (Modiolodon). The Modiolodon of Ulrich includes some American Ordovician marine modiolopsoid shells having two or three strongly radial cardinal teeth in each valve. The Modiolodon of Netschayew includes some Russian fresh-water Permian modiolopsoid shells having two or three cardinal teeth in each valve but differing from the American Ordovician shells in having the teeth horizontal instead of radial. Both genera differ from Modiomorpha in having more numerous cardinal teeth.