Specimen of Trimerella, from Modzalevskaya (2003), via Christopher Taylor's Taxon Diversity.
Middle Ordovician to late Silurian
Shell aragonite, with muscle platform. Ordovician to Silurian.
"Brachiopods of this superfamily are both progressive and divergent from the Obolidae, with posterior platforms to which some of the muscles were attached. More advanced forms have rudimentary articulation and a generally prominent ventral cardinal area that is triangular and transversely 'striated. The shells are thick and decidedly inequivalved. Cambrian to Silurian. Trimerella (Silurian) is representative of the superfamily and is an important index fossil. " - Twenhofel, W. H., and Shrock, R. R., Invertebrate Paleontology, 1935. McGraw- Hill Book Co., N. Y. p.287 (copyright expired)
Includes only the Superfamily Trimerellacea / -oidea.
Originally three families, the Neobolidae, Elkaniidae and Trimerellidae, were included in this superfamily, the first two formerly under the Obolidae (Obolacea). More recently, the following families are included:
Modzalevskaya, T. L. 2003. Silurian and Devonian brachiopods from Severnaya Zemlya (Russian Arctic). Geodiversitas 25 (1): 73-107.
Brachiopoda main page