Middle Ordovician – Middle Permian
Platyceratidae is an extinct family of passively mobile epifaunal detritivores.
Description of the Family
- Earlier members turbiniform or naticiform
- Highly difficult to differentiate due to the vast variety of morphological characteristics
Treatise on Invertebrate Paleontology, Part I, Mollusca 1 (1960):
- Coprophagous on crinoids and cystoids (Bowsher, 1955), the shells showing through their range from mid-Ordovician to late Paleozoic progressively more complete adaptation to a stationary life, principally on crinoid calices; earlier members turbiniform or naticiform, with flat columellar lip but with irregular prosocline growth line; lip becoming more uneven, conforming to irregularities of the crinoid or cystoid calyx, and the primitively coiled shell uncoiling or developing other peculiarities of growth as crinoids became more elaborate in the course of time; ornament present in more primitive stocks but gradually lost.
- So great is the variability induced by the stationary habit that systematics of the group are unusually difficult. One has trouble in deciding if two markedly unlike variations represent different genera or subgenera, or are actually conspecific. In the Platyceratidae the outer shell layers are relatively thick and calcitic, so that specimens resist solution noticeably better than many gastropods that are more largely aragonitic. The inner shell layers of the primitive genus Cyclonema are seemingly nacreous and aragonitic, but this layer appears to be lost in the more advanced Platyceras.