Nebraska Invertebrate Fossils - Brachiopod Fossils from the Stull Shale Late Pennsylvanian (Virgilian), Cass County, Nebraska

Inarticulate

All of the previously viewed brachiopods are called articulate brachiopods---that is, they open their shells with a system of teeth and sockets that serve as a hinge that is controlled by adductor and diductor muscles that close and open the valves when the need arose. Inarticulate brachiopods, however, have no teeth or sockets and open their shells by an entirely muscular and ligament process. Articulate brachiopods have calcium carbonate shells whereas inarticulate brachiopods have calcium phosphate shells. The larval lives and stages of the two kinds of brachiopods are also different.

Terebratuloid

These are characterized by having ovate, smooth shells with pedicle openings. See the examples of recent brachiopods from New Zealand. Most extant brachiopods are terebratuloids, which appear to be closely related to such forms as the atrypoid brachipods such as Composita. Such is not the case. The former has its food gathering system supported by a large, single loop inside the shell whereas the latter has it food gathering system supported by spiralia.

Atrypoid

Atrypoid brachiopods are similar to spiriferoid brachiopods inasmuch as they also have spiralia. Atrypoid brachiopods, however, have short hinge lines and their shells may be either smooth or plicated.

Note on Composita: In their classic 1932 study "Brachiopoda of the Pennsylvanian System in Nebraska" Carl O. Dunbar and George E. Condra recorded at least four species of Composita from Nebraska. These are shown in the illustrations for your reference. Subsequent workers such as Norman Newell in Kansas and Myron Sturgeon and Richard Hoare in Ohio continued to recognize the species that were recognized or erected by Dunbar and Condra. Anne Lutz-Garihan studied a large number of Composita from the early Permian strata of Kansas and Oklahoma and showed that the genus was represented by an intergradational series of individuals that varied morphologically between two end members and none could be separated into groups that could be interpreted as separate species. Further, Lutz-Garihan showed that the end members did not differ in abundance and distribution in rock types, stratigraphic horizons or geographic areas and could not be explained as ecophenotypes, evolutionary populations or subspecies. Although Composita and its species have not been studied in the same detail as Lutz Garrihan's material, the genus shows a great variation in the Stull Shale of Nebraska, Iowa and Kansas.

Spiriferoid

Spiriferoid brachiopods usually have long hinge lines and well-developed teeth and sockets. They have plicated or coarsely ribbed shells and probably attached to the substrate by a fleshy pedicle that protruded through a large, V-shaped pedicle opening. Their name is derived from a pair of internal structures called spiralia which are shaped like coil springs. The spiralia supported their food gathering mechanisms that in modern brachiopods resemble feathery tentacles.

Strophomenoid

These brachiopods can become rather large, some having shells of 75 mm (3 inches) in diameter. Their pedicle opinings are usually filled with small calcite plates. Strophomenoid brachiopods probably remained immobile in the mud into which the extended their long, steeple-like beaks. The valves are commonly flattened toward the anterior and they have a circular outline with very fine costae. These brachiopods often have very well developed muscle scars on their interiors. Derbyia, Schuchertella and Streptorhynchus appear to be the most common genera of strophomenoid brachiopods in Nebraska.

Chonetoid

Chonetoid brachiopods are typified by having nearly semi-circular shells with flat to only slightly inflated brachial and pedicle valves. They have spines along the hinge line of the pedicle valve and the pedicle opening is closed up with tiny plates. Chonetoid brachiopods appear to be most common in fairly muddy water environments. They may have fixed themselves to the substrate by sinking their spines in the muddy bottom. There are a number of genera of chonetoid brachiopods with the suffix " —chonetes" which should be pronounced "cone eat ease".

Productoid

Productoid brachiopods are characterized by having highly inflated, and spinose pedicle valves, long hinge lines, and large beaks. The spines may be several inches long. Some genera such as Antiquatonia have but a few robust spines whereas others such as Pulchratia have numerous, fine spines. Some productoid brachiopods probably settled into a soft substrate by imbedding their spines in the soft substrate whereas some productoids appear to have cemented their spines to a hard object in the substrate. There are several distinct species of productoids in the Pennsylvanian of the mid-continent. Growth series have generally not been constructed for many of these brachiopods so it is not known which "species" are valid and which are growth stages of a described species.

Orthoid

These brachiopods often had large beaks that may have been pressed into the mud to stabilize the shell. Orthoids usually have highly inflated valves with very fine costae and short hinge lines. There are only two genera of these rather primitive brachiopods that have been recorded in Nebraska: Enteletes and Rhipidomella.

Rhynchonelloid

These small brachiopods are usually wedge shaped, they have sharply pointed beaks and minute pedicle openings. The pedicle valves have deep folds with coarse plications. They appear to be represented by only two species in Nebraska, Wellerella osagensis (Swallow) and Rhynchopora sp.