Paterinida

(Early Cambrian to Late Ordovician)

Representative Paterinida: Dictyonina, Early to Middle Cambrian. The surface is marked by obliquely intersecting rows of minute pits  Dictyonina pannula (White) (a, b, pedicle valve), Middle Cambrian, Nevada, width 3 mm Micromitra, Early to Middle Cambrian. The surface is marked by concentric lines and low radial ridges.  Micromitra sculptilis (Meek) (a, b, pedicle valve; c.brachial valve), Middle Cambrian, Montana. width 4 mm

from Moore, Lalicker and Fischer, Invertebrate Fossils, McGraw-Hill Book Company Inc, 1952, pp.224-5

This small group of  Linguliform inarticulate brachiopods includes only about 14 known genera. They seem to be only distantly related to all other brachiopods.

These tiny brachiopods possess chitinophosphatic shells, mostly having maximum dimensions of  2 to 7.5 mm and characterized by a distinct palintrope on the pedicle valve. The delthyrium is largely closed by a homeodeltidium. Growth of the pedicle valve is mixo-peripheral, as shown by presence of a palintrope. That of the brachial valve is hemiperipheral. The larval shells are pustulose. The cardinal margins lack setae.

A shell consisting of chitino-phosphate would seem to indicate they are typical "inarticulates", whilst  the biconvex valves with their essentially straight posterior margin, well developed pseudointeraea and medianly arched plates resemble the articulates. Wright 1979) suggests they constitute one of a number of groups of "brachiophorates" which developed a skeleton independently from other stocks. The more recent classification on the EuroBrachNet site favours distant relationships with the lingulids

Previously ranked as the Superfamily Paterinacea, these brachiopods have since been elevated to ordinal, and now (perhaps undeservedly for such a small group) class status. The group is mostly limited to the early to middle Cambrian period, with a few stragglers making it through to the Late Ordovician. They are representatives of the first evolutionary wave of invertebrates (the Tommotian biota)

References

A. D. Wright, "Brachiopod Radiation", in Systematics Association Special Volume No.12, The Origin of Major Invertebrate Groups, ed. by M. R. House, 1979, pp.235-252, Academic Press, London and New York