Taxonomy and evolution
Gigantoproductus sp.
Diagnosis:
- Commonly gigantic, transverse ribbing across valve but commonly irregular
- Tending to be weakened towards anterior, ventral valve (pedicle) thickened with pits accommodating dorsal brachial cones, cardinal process trifid
As a group the Productida evolved during the Devonian, the first distinct productids are found in strata from the Emsian, approximately 407mya. The lineage in which Gigantoproductus is found dates back to the very basal part of the Emsian and as such is probably the lineage from which all other productid groups evolved.
The ancestor of all productids was a Chonetid like brachiopod. Chonetids are a group of brachiopods with a roughly semi-circular outline and tend to be concavo-convex or plano-convex. They also tend to be small (1-3cm in width at most) and often have a small number of spines on the strophic (straight) hinge-line which probably served to stabilise the animal on or in the sediment. It was the spreading of these spines all over the pedicle valve which characterises the evolution of the productids from the chonetids.