Petrocrania

Classification
Phylum: Brachiopoda
Class: Craniata
Order: Craniida
Family: Craniidae
Genus: Petrocrania Raymond, 1911
Cincinnatian Species: Petrocrania scabiosa

Taxonomic Details

Synonym: Philhedrella Kozlowski, 1929

Geologic Range
Lower Ordovician – Lower Carboniferous

Common Paleoecology
Petrocrania is an extinct genus of stationary, epifaunal suspension feeders.

Identification in Hand Sample:

  • Encrusting brachiopod commonly found on surface of other shells
  • Circular, small and very thin
  • Ornamentation of underlying shell visible through Petrocrania
  • Sometimes, concentric growth lines visiblie
  • Composed of calcareous shell

Geographic Occurrences

		
Map point data provided by iDigBio.

Published Description

Treatise on Invertebrate Paleontology, Part H, Vol. 2 (2000):

  • Dorsal valve convex to subconical; beak subcentral to posterocentral;
    ornament only of concentric growth laminae or simulating morphology of the host;
    dorsal posterior adductor scars typically larger than anterior scars, but not
    exclusively; vascular lateralia commonly prominent, sigmoidal; valve margin not
    thickened, limbus narrow when developed ; encrusting; ventral valve not known.

Fossils of Ohio (1996):

  • A small to medium sized- acrotretid brachiopod. It has a circular outline and
    a calcareous shell. This brachiopod commonly is found attached to other types of
    shells, such as that of the articulate brachiopod Rafinesquina. Because the shell of
    Petrocrania is very thin, the ornament of the underlying surface to which this
    brachiopod has attached is commonly visible. Petrocrania is recorded from the
    entire Cincinnatian Series and also is found in Silurian and Devonian rocks of Ohio

William (1974):

  • Exterior of brachial valve slightly irregular, subquadrate and suboval with
    flattened posterior margin, 82% as long as wide (mean for 4 valves). And 26% as
    deep as long (mean for 3 valves) with maximum depth at about mid-point; surface
    with sporadic concentric growth lines, otherwise smooth; shell with thickened
    slightly averted margin corresponding to limbus about 1 mm wide.
  • Interior of brachial valve with strongly impressed suboval postero-lateral
    adductor scars smaller than suboval elevated anterior adductor scars situated
    submedially up to 60% forward of the posterior margin and ornamented by fine
    parallel wavy ridges; mantle canal system pinnate with variably impressed
    sigmoidal vascular lateralia.

Caster, Dalve, & Pope (1961):

  • The inarticulate brachiopods are distinguished from the articulate forms by the absence of a hinge, a different musculature, and shells of calcium phosphate-chitin rather than calcium carbonate. In the Cincinnatian these may be frequently seen as thin, oval shells adhering to larger brachiopod shells (Petrocrania, Schizocrania), as chalky shells with minute punctae (pores) in the valves (Trematis) or as glossy, triangular shells (“Lingula”). Since the inarticulates appear in the Cambrian before the articulates, they are considered the evolutionary precursor of the articulates.

P. scabiosa